worker.c

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/*-------------------------------------------------------------------------
 * worker.c
 *     PostgreSQL logical replication worker (apply)
 *
 * Copyright (c) 2016-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/replication/logical/worker.c
 *
 * NOTES
 *    This file contains the worker which applies logical changes as they come
 *    from remote logical replication stream.
 *
 *    The main worker (apply) is started by logical replication worker
 *    launcher for every enabled subscription in a database. It uses
 *    walsender protocol to communicate with publisher.
 *
 *    This module includes server facing code and shares libpqwalreceiver
 *    module with walreceiver for providing the libpq specific functionality.
 *
 *
 * STREAMED TRANSACTIONS
 * ---------------------
 * Streamed transactions (large transactions exceeding a memory limit on the
 * upstream) are applied using one of two approaches:
 *
 * 1) Write to temporary files and apply when the final commit arrives
 *
 * This approach is used when the user has set the subscription's streaming
 * option as on.
 *
 * Unlike the regular (non-streamed) case, handling streamed transactions has
 * to handle aborts of both the toplevel transaction and subtransactions. This
 * is achieved by tracking offsets for subtransactions, which is then used
 * to truncate the file with serialized changes.
 *
 * The files are placed in tmp file directory by default, and the filenames
 * include both the XID of the toplevel transaction and OID of the
 * subscription. This is necessary so that different workers processing a
 * remote transaction with the same XID doesn't interfere.
 *
 * We use BufFiles instead of using normal temporary files because (a) the
 * BufFile infrastructure supports temporary files that exceed the OS file size
 * limit, (b) provides a way for automatic clean up on the error and (c) provides
 * a way to survive these files across local transactions and allow to open and
 * close at stream start and close. We decided to use FileSet
 * infrastructure as without that it deletes the files on the closure of the
 * file and if we decide to keep stream files open across the start/stop stream
 * then it will consume a lot of memory (more than 8K for each BufFile and
 * there could be multiple such BufFiles as the subscriber could receive
 * multiple start/stop streams for different transactions before getting the
 * commit). Moreover, if we don't use FileSet then we also need to invent
 * a new way to pass filenames to BufFile APIs so that we are allowed to open
 * the file we desired across multiple stream-open calls for the same
 * transaction.
 *
 * 2) Parallel apply workers.
 *
 * This approach is used when the user has set the subscription's streaming
 * option as parallel. See logical/applyparallelworker.c for information about
 * this approach.
 *
 * TWO_PHASE TRANSACTIONS
 * ----------------------
 * Two phase transactions are replayed at prepare and then committed or
 * rolled back at commit prepared and rollback prepared respectively. It is
 * possible to have a prepared transaction that arrives at the apply worker
 * when the tablesync is busy doing the initial copy. In this case, the apply
 * worker skips all the prepared operations [e.g. inserts] while the tablesync
 * is still busy (see the condition of should_apply_changes_for_rel). The
 * tablesync worker might not get such a prepared transaction because say it
 * was prior to the initial consistent point but might have got some later
 * commits. Now, the tablesync worker will exit without doing anything for the
 * prepared transaction skipped by the apply worker as the sync location for it
 * will be already ahead of the apply worker's current location. This would lead
 * to an "empty prepare", because later when the apply worker does the commit
 * prepare, there is nothing in it (the inserts were skipped earlier).
 *
 * To avoid this, and similar prepare confusions the subscription's two_phase
 * commit is enabled only after the initial sync is over. The two_phase option
 * has been implemented as a tri-state with values DISABLED, PENDING, and
 * ENABLED.
 *
 * Even if the user specifies they want a subscription with two_phase = on,
 * internally it will start with a tri-state of PENDING which only becomes
 * ENABLED after all tablesync initializations are completed - i.e. when all
 * tablesync workers have reached their READY state. In other words, the value
 * PENDING is only a temporary state for subscription start-up.
 *
 * Until the two_phase is properly available (ENABLED) the subscription will
 * behave as if two_phase = off. When the apply worker detects that all
 * tablesyncs have become READY (while the tri-state was PENDING) it will
 * restart the apply worker process. This happens in
 * process_syncing_tables_for_apply.
 *
 * When the (re-started) apply worker finds that all tablesyncs are READY for a
 * two_phase tri-state of PENDING it start streaming messages with the
 * two_phase option which in turn enables the decoding of two-phase commits at
 * the publisher. Then, it updates the tri-state value from PENDING to ENABLED.
 * Now, it is possible that during the time we have not enabled two_phase, the
 * publisher (replication server) would have skipped some prepares but we
 * ensure that such prepares are sent along with commit prepare, see
 * ReorderBufferFinishPrepared.
 *
 * If the subscription has no tables then a two_phase tri-state PENDING is
 * left unchanged. This lets the user still do an ALTER SUBSCRIPTION REFRESH
 * PUBLICATION which might otherwise be disallowed (see below).
 *
 * If ever a user needs to be aware of the tri-state value, they can fetch it
 * from the pg_subscription catalog (see column subtwophasestate).
 *
 * Finally, to avoid problems mentioned in previous paragraphs from any
 * subsequent (not READY) tablesyncs (need to toggle two_phase option from 'on'
 * to 'off' and then again back to 'on') there is a restriction for
 * ALTER SUBSCRIPTION REFRESH PUBLICATION. This command is not permitted when
 * the two_phase tri-state is ENABLED, except when copy_data = false.
 *
 * We can get prepare of the same GID more than once for the genuine cases
 * where we have defined multiple subscriptions for publications on the same
 * server and prepared transaction has operations on tables subscribed to those
 * subscriptions. For such cases, if we use the GID sent by publisher one of
 * the prepares will be successful and others will fail, in which case the
 * server will send them again. Now, this can lead to a deadlock if user has
 * set synchronous_standby_names for all the subscriptions on subscriber. To
 * avoid such deadlocks, we generate a unique GID (consisting of the
 * subscription oid and the xid of the prepared transaction) for each prepare
 * transaction on the subscriber.
 *
 * FAILOVER
 * ----------------------
 * The logical slot on the primary can be synced to the standby by specifying
 * failover = true when creating the subscription. Enabling failover allows us
 * to smoothly transition to the promoted standby, ensuring that we can
 * subscribe to the new primary without losing any data.
 *
 * RETAIN DEAD TUPLES
 * ----------------------
 * Each apply worker that enabled retain_dead_tuples option maintains a
 * non-removable transaction ID (oldest_nonremovable_xid) in shared memory to
 * prevent dead rows from being removed prematurely when the apply worker still
 * needs them to detect update_deleted conflicts. Additionally, this helps to
 * retain the required commit_ts module information, which further helps to
 * detect update_origin_differs and delete_origin_differs conflicts reliably, as
 * otherwise, vacuum freeze could remove the required information.
 *
 * The logical replication launcher manages an internal replication slot named
 * "pg_conflict_detection". It asynchronously aggregates the non-removable
 * transaction ID from all apply workers to determine the appropriate xmin for
 * the slot, thereby retaining necessary tuples.
 *
 * The non-removable transaction ID in the apply worker is advanced to the
 * oldest running transaction ID once all concurrent transactions on the
 * publisher have been applied and flushed locally. The process involves:
 *
 * - RDT_GET_CANDIDATE_XID:
 *   Call GetOldestActiveTransactionId() to take oldestRunningXid as the
 *   candidate xid.
 *
 * - RDT_REQUEST_PUBLISHER_STATUS:
 *   Send a message to the walsender requesting the publisher status, which
 *   includes the latest WAL write position and information about transactions
 *   that are in the commit phase.
 *
 * - RDT_WAIT_FOR_PUBLISHER_STATUS:
 *   Wait for the status from the walsender. After receiving the first status,
 *   do not proceed if there are concurrent remote transactions that are still
 *   in the commit phase. These transactions might have been assigned an
 *   earlier commit timestamp but have not yet written the commit WAL record.
 *   Continue to request the publisher status (RDT_REQUEST_PUBLISHER_STATUS)
 *   until all these transactions have completed.
 *
 * - RDT_WAIT_FOR_LOCAL_FLUSH:
 *   Advance the non-removable transaction ID if the current flush location has
 *   reached or surpassed the last received WAL position.
 *
 * - RDT_STOP_CONFLICT_INFO_RETENTION:
 *   This phase is required only when max_retention_duration is defined. We
 *   enter this phase if the wait time in either the
 *   RDT_WAIT_FOR_PUBLISHER_STATUS or RDT_WAIT_FOR_LOCAL_FLUSH phase exceeds
 *   configured max_retention_duration. In this phase,
 *   pg_subscription.subretentionactive is updated to false within a new
 *   transaction, and oldest_nonremovable_xid is set to InvalidTransactionId.
 *
 * - RDT_RESUME_CONFLICT_INFO_RETENTION:
 *   This phase is required only when max_retention_duration is defined. We
 *   enter this phase if the retention was previously stopped, and the time
 *   required to advance the non-removable transaction ID in the
 *   RDT_WAIT_FOR_LOCAL_FLUSH phase has decreased to within acceptable limits
 *   (or if max_retention_duration is set to 0). During this phase,
 *   pg_subscription.subretentionactive is updated to true within a new
 *   transaction, and the worker will be restarted.
 *
 * The overall state progression is: GET_CANDIDATE_XID ->
 * REQUEST_PUBLISHER_STATUS -> WAIT_FOR_PUBLISHER_STATUS -> (loop to
 * REQUEST_PUBLISHER_STATUS till concurrent remote transactions end) ->
 * WAIT_FOR_LOCAL_FLUSH -> loop back to GET_CANDIDATE_XID.
 *
 * Retaining the dead tuples for this period is sufficient for ensuring
 * eventual consistency using last-update-wins strategy, as dead tuples are
 * useful for detecting conflicts only during the application of concurrent
 * transactions from remote nodes. After applying and flushing all remote
 * transactions that occurred concurrently with the tuple DELETE, any
 * subsequent UPDATE from a remote node should have a later timestamp. In such
 * cases, it is acceptable to detect an update_missing scenario and convert the
 * UPDATE to an INSERT when applying it. But, for concurrent remote
 * transactions with earlier timestamps than the DELETE, detecting
 * update_deleted is necessary, as the UPDATEs in remote transactions should be
 * ignored if their timestamp is earlier than that of the dead tuples.
 *
 * Note that advancing the non-removable transaction ID is not supported if the
 * publisher is also a physical standby. This is because the logical walsender
 * on the standby can only get the WAL replay position but there may be more
 * WALs that are being replicated from the primary and those WALs could have
 * earlier commit timestamp.
 *
 * Similarly, when the publisher has subscribed to another publisher,
 * information necessary for conflict detection cannot be retained for
 * changes from origins other than the publisher. This is because publisher
 * lacks the information on concurrent transactions of other publishers to
 * which it subscribes. As the information on concurrent transactions is
 * unavailable beyond subscriber's immediate publishers, the non-removable
 * transaction ID might be advanced prematurely before changes from other
 * origins have been fully applied.
 *
 * XXX Retaining information for changes from other origins might be possible
 * by requesting the subscription on that origin to enable retain_dead_tuples
 * and fetching the conflict detection slot.xmin along with the publisher's
 * status. In the RDT_WAIT_FOR_PUBLISHER_STATUS phase, the apply worker could
 * wait for the remote slot's xmin to reach the oldest active transaction ID,
 * ensuring that all transactions from other origins have been applied on the
 * publisher, thereby getting the latest WAL position that includes all
 * concurrent changes. However, this approach may impact performance, so it
 * might not worth the effort.
 *
 * XXX It seems feasible to get the latest commit's WAL location from the
 * publisher and wait till that is applied. However, we can't do that
 * because commit timestamps can regress as a commit with a later LSN is not
 * guaranteed to have a later timestamp than those with earlier LSNs. Having
 * said that, even if that is possible, it won't improve performance much as
 * the apply always lag and moves slowly as compared with the transactions
 * on the publisher.
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <sys/stat.h>
#include <unistd.h>
 
#include "access/commit_ts.h"
#include "access/table.h"
#include "access/tableam.h"
#include "access/twophase.h"
#include "access/xact.h"
#include "catalog/indexing.h"
#include "catalog/pg_inherits.h"
#include "catalog/pg_subscription.h"
#include "catalog/pg_subscription_rel.h"
#include "commands/subscriptioncmds.h"
#include "commands/tablecmds.h"
#include "commands/trigger.h"
#include "executor/executor.h"
#include "executor/execPartition.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
#include "optimizer/optimizer.h"
#include "parser/parse_relation.h"
#include "pgstat.h"
#include "postmaster/bgworker.h"
#include "postmaster/interrupt.h"
#include "postmaster/walwriter.h"
#include "replication/conflict.h"
#include "replication/logicallauncher.h"
#include "replication/logicalproto.h"
#include "replication/logicalrelation.h"
#include "replication/logicalworker.h"
#include "replication/origin.h"
#include "replication/slot.h"
#include "replication/walreceiver.h"
#include "replication/worker_internal.h"
#include "rewrite/rewriteHandler.h"
#include "storage/buffile.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
#include "storage/procarray.h"
#include "tcop/tcopprot.h"
#include "utils/acl.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/pg_lsn.h"
#include "utils/rel.h"
#include "utils/rls.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
#include "utils/usercontext.h"
 
#define NAPTIME_PER_CYCLE 1000  /* max sleep time between cycles (1s) */
 
typedef struct FlushPosition
{
    dlist_node  node;
    XLogRecPtr  local_end;
    XLogRecPtr  remote_end;
} FlushPosition;
 
static dlist_head lsn_mapping = DLIST_STATIC_INIT(lsn_mapping);
 
typedef struct ApplyExecutionData
{
    EState     *estate;         /* executor state, used to track resources */
 
    LogicalRepRelMapEntry *targetRel;   /* replication target rel */
    ResultRelInfo *targetRelInfo;   /* ResultRelInfo for same */
 
    /* These fields are used when the target relation is partitioned: */
    ModifyTableState *mtstate;  /* dummy ModifyTable state */
    PartitionTupleRouting *proute;  /* partition routing info */
} ApplyExecutionData;
 
/* Struct for saving and restoring apply errcontext information */
typedef struct ApplyErrorCallbackArg
{
    LogicalRepMsgType command;  /* 0 if invalid */
    LogicalRepRelMapEntry *rel;
 
    /* Remote node information */
    int         remote_attnum;  /* -1 if invalid */
    TransactionId remote_xid;
    XLogRecPtr  finish_lsn;
    char       *origin_name;
} ApplyErrorCallbackArg;
 
/*
 * The action to be taken for the changes in the transaction.
 *
 * TRANS_LEADER_APPLY:
 * This action means that we are in the leader apply worker or table sync
 * worker. The changes of the transaction are either directly applied or
 * are read from temporary files (for streaming transactions) and then
 * applied by the worker.
 *
 * TRANS_LEADER_SERIALIZE:
 * This action means that we are in the leader apply worker or table sync
 * worker. Changes are written to temporary files and then applied when the
 * final commit arrives.
 *
 * TRANS_LEADER_SEND_TO_PARALLEL:
 * This action means that we are in the leader apply worker and need to send
 * the changes to the parallel apply worker.
 *
 * TRANS_LEADER_PARTIAL_SERIALIZE:
 * This action means that we are in the leader apply worker and have sent some
 * changes directly to the parallel apply worker and the remaining changes are
 * serialized to a file, due to timeout while sending data. The parallel apply
 * worker will apply these serialized changes when the final commit arrives.
 *
 * We can't use TRANS_LEADER_SERIALIZE for this case because, in addition to
 * serializing changes, the leader worker also needs to serialize the
 * STREAM_XXX message to a file, and wait for the parallel apply worker to
 * finish the transaction when processing the transaction finish command. So
 * this new action was introduced to keep the code and logic clear.
 *
 * TRANS_PARALLEL_APPLY:
 * This action means that we are in the parallel apply worker and changes of
 * the transaction are applied directly by the worker.
 */
typedef enum
{
    /* The action for non-streaming transactions. */
    TRANS_LEADER_APPLY,
 
    /* Actions for streaming transactions. */
    TRANS_LEADER_SERIALIZE,
    TRANS_LEADER_SEND_TO_PARALLEL,
    TRANS_LEADER_PARTIAL_SERIALIZE,
    TRANS_PARALLEL_APPLY,
} TransApplyAction;
 
/*
 * The phases involved in advancing the non-removable transaction ID.
 *
 * See comments atop worker.c for details of the transition between these
 * phases.
 */
typedef enum
{
    RDT_GET_CANDIDATE_XID,
    RDT_REQUEST_PUBLISHER_STATUS,
    RDT_WAIT_FOR_PUBLISHER_STATUS,
    RDT_WAIT_FOR_LOCAL_FLUSH,
    RDT_STOP_CONFLICT_INFO_RETENTION,
    RDT_RESUME_CONFLICT_INFO_RETENTION,
} RetainDeadTuplesPhase;
 
/*
 * Critical information for managing phase transitions within the
 * RetainDeadTuplesPhase.
 */
typedef struct RetainDeadTuplesData
{
    RetainDeadTuplesPhase phase;    /* current phase */
    XLogRecPtr  remote_lsn;     /* WAL write position on the publisher */
 
    /*
     * Oldest transaction ID that was in the commit phase on the publisher.
     * Use FullTransactionId to prevent issues with transaction ID wraparound,
     * where a new remote_oldestxid could falsely appear to originate from the
     * past and block advancement.
     */
    FullTransactionId remote_oldestxid;
 
    /*
     * Next transaction ID to be assigned on the publisher. Use
     * FullTransactionId for consistency and to allow straightforward
     * comparisons with remote_oldestxid.
     */
    FullTransactionId remote_nextxid;
 
    TimestampTz reply_time;     /* when the publisher responds with status */
 
    /*
     * Publisher transaction ID that must be awaited to complete before
     * entering the final phase (RDT_WAIT_FOR_LOCAL_FLUSH). Use
     * FullTransactionId for the same reason as remote_nextxid.
     */
    FullTransactionId remote_wait_for;
 
    TransactionId candidate_xid;    /* candidate for the non-removable
                                     * transaction ID */
    TimestampTz flushpos_update_time;   /* when the remote flush position was
                                         * updated in final phase
                                         * (RDT_WAIT_FOR_LOCAL_FLUSH) */
 
    long        table_sync_wait_time;   /* time spent waiting for table sync
                                         * to finish */
 
    /*
     * The following fields are used to determine the timing for the next
     * round of transaction ID advancement.
     */
    TimestampTz last_recv_time; /* when the last message was received */
    TimestampTz candidate_xid_time; /* when the candidate_xid is decided */
    int         xid_advance_interval;   /* how much time (ms) to wait before
                                         * attempting to advance the
                                         * non-removable transaction ID */
} RetainDeadTuplesData;
 
/*
 * The minimum (100ms) and maximum (3 minutes) intervals for advancing
 * non-removable transaction IDs. The maximum interval is a bit arbitrary but
 * is sufficient to not cause any undue network traffic.
 */
#define MIN_XID_ADVANCE_INTERVAL 100
#define MAX_XID_ADVANCE_INTERVAL 180000
 
/* errcontext tracker */
static ApplyErrorCallbackArg apply_error_callback_arg =
{
    .command = 0,
    .rel = NULL,
    .remote_attnum = -1,
    .remote_xid = InvalidTransactionId,
    .finish_lsn = InvalidXLogRecPtr,
    .origin_name = NULL,
};
 
ErrorContextCallback *apply_error_context_stack = NULL;
 
MemoryContext ApplyMessageContext = NULL;
MemoryContext ApplyContext = NULL;
 
/* per stream context for streaming transactions */
static MemoryContext LogicalStreamingContext = NULL;
 
WalReceiverConn *LogRepWorkerWalRcvConn = NULL;
 
Subscription *MySubscription = NULL;
static bool MySubscriptionValid = false;
 
static List *on_commit_wakeup_workers_subids = NIL;
 
bool        in_remote_transaction = false;
static XLogRecPtr remote_final_lsn = InvalidXLogRecPtr;
 
/* fields valid only when processing streamed transaction */
static bool in_streamed_transaction = false;
 
static TransactionId stream_xid = InvalidTransactionId;
 
/*
 * The number of changes applied by parallel apply worker during one streaming
 * block.
 */
static uint32 parallel_stream_nchanges = 0;
 
/* Are we initializing an apply worker? */
bool        InitializingApplyWorker = false;
 
/*
 * We enable skipping all data modification changes (INSERT, UPDATE, etc.) for
 * the subscription if the remote transaction's finish LSN matches the subskiplsn.
 * Once we start skipping changes, we don't stop it until we skip all changes of
 * the transaction even if pg_subscription is updated and MySubscription->skiplsn
 * gets changed or reset during that. Also, in streaming transaction cases (streaming = on),
 * we don't skip receiving and spooling the changes since we decide whether or not
 * to skip applying the changes when starting to apply changes. The subskiplsn is
 * cleared after successfully skipping the transaction or applying non-empty
 * transaction. The latter prevents the mistakenly specified subskiplsn from
 * being left. Note that we cannot skip the streaming transactions when using
 * parallel apply workers because we cannot get the finish LSN before applying
 * the changes. So, we don't start parallel apply worker when finish LSN is set
 * by the user.
 */
static XLogRecPtr skip_xact_finish_lsn = InvalidXLogRecPtr;
#define is_skipping_changes() (unlikely(!XLogRecPtrIsInvalid(skip_xact_finish_lsn)))
 
/* BufFile handle of the current streaming file */
static BufFile *stream_fd = NULL;
 
/*
 * The remote WAL position that has been applied and flushed locally. We record
 * and use this information both while sending feedback to the server and
 * advancing oldest_nonremovable_xid.
 */
static XLogRecPtr last_flushpos = InvalidXLogRecPtr;
 
typedef struct SubXactInfo
{
    TransactionId xid;          /* XID of the subxact */
    int         fileno;         /* file number in the buffile */
    off_t       offset;         /* offset in the file */
} SubXactInfo;
 
/* Sub-transaction data for the current streaming transaction */
typedef struct ApplySubXactData
{
    uint32      nsubxacts;      /* number of sub-transactions */
    uint32      nsubxacts_max;  /* current capacity of subxacts */
    TransactionId subxact_last; /* xid of the last sub-transaction */
    SubXactInfo *subxacts;      /* sub-xact offset in changes file */
} ApplySubXactData;
 
static ApplySubXactData subxact_data = {0, 0, InvalidTransactionId, NULL};
 
static inline void subxact_filename(char *path, Oid subid, TransactionId xid);
static inline void changes_filename(char *path, Oid subid, TransactionId xid);
 
/*
 * Information about subtransactions of a given toplevel transaction.
 */
static void subxact_info_write(Oid subid, TransactionId xid);
static void subxact_info_read(Oid subid, TransactionId xid);
static void subxact_info_add(TransactionId xid);
static inline void cleanup_subxact_info(void);
 
/*
 * Serialize and deserialize changes for a toplevel transaction.
 */
static void stream_open_file(Oid subid, TransactionId xid,
                             bool first_segment);
static void stream_write_change(char action, StringInfo s);
static void stream_open_and_write_change(TransactionId xid, char action, StringInfo s);
static void stream_close_file(void);
 
static void send_feedback(XLogRecPtr recvpos, bool force, bool requestReply);
 
static void maybe_advance_nonremovable_xid(RetainDeadTuplesData *rdt_data,
                                           bool status_received);
static bool can_advance_nonremovable_xid(RetainDeadTuplesData *rdt_data);
static void process_rdt_phase_transition(RetainDeadTuplesData *rdt_data,
                                         bool status_received);
static void get_candidate_xid(RetainDeadTuplesData *rdt_data);
static void request_publisher_status(RetainDeadTuplesData *rdt_data);
static void wait_for_publisher_status(RetainDeadTuplesData *rdt_data,
                                      bool status_received);
static void wait_for_local_flush(RetainDeadTuplesData *rdt_data);
static bool should_stop_conflict_info_retention(RetainDeadTuplesData *rdt_data);
static void stop_conflict_info_retention(RetainDeadTuplesData *rdt_data);
static void resume_conflict_info_retention(RetainDeadTuplesData *rdt_data);
static bool update_retention_status(bool active);
static void reset_retention_data_fields(RetainDeadTuplesData *rdt_data);
static void adjust_xid_advance_interval(RetainDeadTuplesData *rdt_data,
                                        bool new_xid_found);
 
static void apply_worker_exit(void);
 
static void apply_handle_commit_internal(LogicalRepCommitData *commit_data);
static void apply_handle_insert_internal(ApplyExecutionData *edata,
                                         ResultRelInfo *relinfo,
                                         TupleTableSlot *remoteslot);
static void apply_handle_update_internal(ApplyExecutionData *edata,
                                         ResultRelInfo *relinfo,
                                         TupleTableSlot *remoteslot,
                                         LogicalRepTupleData *newtup,
                                         Oid localindexoid);
static void apply_handle_delete_internal(ApplyExecutionData *edata,
                                         ResultRelInfo *relinfo,
                                         TupleTableSlot *remoteslot,
                                         Oid localindexoid);
static bool FindReplTupleInLocalRel(ApplyExecutionData *edata, Relation localrel,
                                    LogicalRepRelation *remoterel,
                                    Oid localidxoid,
                                    TupleTableSlot *remoteslot,
                                    TupleTableSlot **localslot);
static bool FindDeletedTupleInLocalRel(Relation localrel,
                                       Oid localidxoid,
                                       TupleTableSlot *remoteslot,
                                       TransactionId *delete_xid,
                                       RepOriginId *delete_origin,
                                       TimestampTz *delete_time);
static void apply_handle_tuple_routing(ApplyExecutionData *edata,
                                       TupleTableSlot *remoteslot,
                                       LogicalRepTupleData *newtup,
                                       CmdType operation);
 
/* Functions for skipping changes */
static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
static void stop_skipping_changes(void);
static void clear_subscription_skip_lsn(XLogRecPtr finish_lsn);
 
/* Functions for apply error callback */
static inline void set_apply_error_context_xact(TransactionId xid, XLogRecPtr lsn);
static inline void reset_apply_error_context_info(void);
 
static TransApplyAction get_transaction_apply_action(TransactionId xid,
                                                     ParallelApplyWorkerInfo **winfo);
 
static void replorigin_reset(int code, Datum arg);
 
/*
 * Form the origin name for the subscription.
 *
 * This is a common function for tablesync and other workers. Tablesync workers
 * must pass a valid relid. Other callers must pass relid = InvalidOid.
 *
 * Return the name in the supplied buffer.
 */
void
ReplicationOriginNameForLogicalRep(Oid suboid, Oid relid,
                                   char *originname, Size szoriginname)
{
    if (OidIsValid(relid))
    {
        /* Replication origin name for tablesync workers. */
        snprintf(originname, szoriginname, "pg_%u_%u", suboid, relid);
    }
    else
    {
        /* Replication origin name for non-tablesync workers. */
        snprintf(originname, szoriginname, "pg_%u", suboid);
    }
}
 
/*
 * Should this worker apply changes for given relation.
 *
 * This is mainly needed for initial relation data sync as that runs in
 * separate worker process running in parallel and we need some way to skip
 * changes coming to the leader apply worker during the sync of a table.
 *
 * Note we need to do smaller or equals comparison for SYNCDONE state because
 * it might hold position of end of initial slot consistent point WAL
 * record + 1 (ie start of next record) and next record can be COMMIT of
 * transaction we are now processing (which is what we set remote_final_lsn
 * to in apply_handle_begin).
 *
 * Note that for streaming transactions that are being applied in the parallel
 * apply worker, we disallow applying changes if the target table in the
 * subscription is not in the READY state, because we cannot decide whether to
 * apply the change as we won't know remote_final_lsn by that time.
 *
 * We already checked this in pa_can_start() before assigning the
 * streaming transaction to the parallel worker, but it also needs to be
 * checked here because if the user executes ALTER SUBSCRIPTION ... REFRESH
 * PUBLICATION in parallel, the new table can be added to pg_subscription_rel
 * while applying this transaction.
 */
static bool
should_apply_changes_for_rel(LogicalRepRelMapEntry *rel)
{
    switch (MyLogicalRepWorker->type)
    {
        case WORKERTYPE_TABLESYNC:
            return MyLogicalRepWorker->relid == rel->localreloid;
 
        case WORKERTYPE_PARALLEL_APPLY:
            /* We don't synchronize rel's that are in unknown state. */
            if (rel->state != SUBREL_STATE_READY &&
                rel->state != SUBREL_STATE_UNKNOWN)
                ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("logical replication parallel apply worker for subscription \"%s\" will stop",
                                MySubscription->name),
                         errdetail("Cannot handle streamed replication transactions using parallel apply workers until all tables have been synchronized.")));
 
            return rel->state == SUBREL_STATE_READY;
 
        case WORKERTYPE_APPLY:
            return (rel->state == SUBREL_STATE_READY ||
                    (rel->state == SUBREL_STATE_SYNCDONE &&
                     rel->statelsn <= remote_final_lsn));
 
        case WORKERTYPE_UNKNOWN:
            /* Should never happen. */
            elog(ERROR, "Unknown worker type");
    }
 
    return false;               /* dummy for compiler */
}
 
/*
 * Begin one step (one INSERT, UPDATE, etc) of a replication transaction.
 *
 * Start a transaction, if this is the first step (else we keep using the
 * existing transaction).
 * Also provide a global snapshot and ensure we run in ApplyMessageContext.
 */
static void
begin_replication_step(void)
{
    SetCurrentStatementStartTimestamp();
 
    if (!IsTransactionState())
    {
        StartTransactionCommand();
        maybe_reread_subscription();
    }
 
    PushActiveSnapshot(GetTransactionSnapshot());
 
    MemoryContextSwitchTo(ApplyMessageContext);
}
 
/*
 * Finish up one step of a replication transaction.
 * Callers of begin_replication_step() must also call this.
 *
 * We don't close out the transaction here, but we should increment
 * the command counter to make the effects of this step visible.
 */
static void
end_replication_step(void)
{
    PopActiveSnapshot();
 
    CommandCounterIncrement();
}
 
/*
 * Handle streamed transactions for both the leader apply worker and the
 * parallel apply workers.
 *
 * In the streaming case (receiving a block of the streamed transaction), for
 * serialize mode, simply redirect it to a file for the proper toplevel
 * transaction, and for parallel mode, the leader apply worker will send the
 * changes to parallel apply workers and the parallel apply worker will define
 * savepoints if needed. (LOGICAL_REP_MSG_RELATION or LOGICAL_REP_MSG_TYPE
 * messages will be applied by both leader apply worker and parallel apply
 * workers).
 *
 * Returns true for streamed transactions (when the change is either serialized
 * to file or sent to parallel apply worker), false otherwise (regular mode or
 * needs to be processed by parallel apply worker).
 *
 * Exception: If the message being processed is LOGICAL_REP_MSG_RELATION
 * or LOGICAL_REP_MSG_TYPE, return false even if the message needs to be sent
 * to a parallel apply worker.
 */
static bool
handle_streamed_transaction(LogicalRepMsgType action, StringInfo s)
{
    TransactionId current_xid;
    ParallelApplyWorkerInfo *winfo;
    TransApplyAction apply_action;
    StringInfoData original_msg;
 
    apply_action = get_transaction_apply_action(stream_xid, &winfo);
 
    /* not in streaming mode */
    if (apply_action == TRANS_LEADER_APPLY)
        return false;
 
    Assert(TransactionIdIsValid(stream_xid));
 
    /*
     * The parallel apply worker needs the xid in this message to decide
     * whether to define a savepoint, so save the original message that has
     * not moved the cursor after the xid. We will serialize this message to a
     * file in PARTIAL_SERIALIZE mode.
     */
    original_msg = *s;
 
    /*
     * We should have received XID of the subxact as the first part of the
     * message, so extract it.
     */
    current_xid = pq_getmsgint(s, 4);
 
    if (!TransactionIdIsValid(current_xid))
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("invalid transaction ID in streamed replication transaction")));
 
    switch (apply_action)
    {
        case TRANS_LEADER_SERIALIZE:
            Assert(stream_fd);
 
            /* Add the new subxact to the array (unless already there). */
            subxact_info_add(current_xid);
 
            /* Write the change to the current file */
            stream_write_change(action, s);
            return true;
 
        case TRANS_LEADER_SEND_TO_PARALLEL:
            Assert(winfo);
 
            /*
             * XXX The publisher side doesn't always send relation/type update
             * messages after the streaming transaction, so also update the
             * relation/type in leader apply worker. See function
             * cleanup_rel_sync_cache.
             */
            if (pa_send_data(winfo, s->len, s->data))
                return (action != LOGICAL_REP_MSG_RELATION &&
                        action != LOGICAL_REP_MSG_TYPE);
 
            /*
             * Switch to serialize mode when we are not able to send the
             * change to parallel apply worker.
             */
            pa_switch_to_partial_serialize(winfo, false);
 
            /* fall through */
        case TRANS_LEADER_PARTIAL_SERIALIZE:
            stream_write_change(action, &original_msg);
 
            /* Same reason as TRANS_LEADER_SEND_TO_PARALLEL case. */
            return (action != LOGICAL_REP_MSG_RELATION &&
                    action != LOGICAL_REP_MSG_TYPE);
 
        case TRANS_PARALLEL_APPLY:
            parallel_stream_nchanges += 1;
 
            /* Define a savepoint for a subxact if needed. */
            pa_start_subtrans(current_xid, stream_xid);
            return false;
 
        default:
            elog(ERROR, "unexpected apply action: %d", (int) apply_action);
            return false;       /* silence compiler warning */
    }
}
 
/*
 * Executor state preparation for evaluation of constraint expressions,
 * indexes and triggers for the specified relation.
 *
 * Note that the caller must open and close any indexes to be updated.
 */
static ApplyExecutionData *
create_edata_for_relation(LogicalRepRelMapEntry *rel)
{
    ApplyExecutionData *edata;
    EState     *estate;
    RangeTblEntry *rte;
    List       *perminfos = NIL;
    ResultRelInfo *resultRelInfo;
 
    edata = (ApplyExecutionData *) palloc0(sizeof(ApplyExecutionData));
    edata->targetRel = rel;
 
    edata->estate = estate = CreateExecutorState();
 
    rte = makeNode(RangeTblEntry);
    rte->rtekind = RTE_RELATION;
    rte->relid = RelationGetRelid(rel->localrel);
    rte->relkind = rel->localrel->rd_rel->relkind;
    rte->rellockmode = AccessShareLock;
 
    addRTEPermissionInfo(&perminfos, rte);
 
    ExecInitRangeTable(estate, list_make1(rte), perminfos,
                       bms_make_singleton(1));
 
    edata->targetRelInfo = resultRelInfo = makeNode(ResultRelInfo);
 
    /*
     * Use Relation opened by logicalrep_rel_open() instead of opening it
     * again.
     */
    InitResultRelInfo(resultRelInfo, rel->localrel, 1, NULL, 0);
 
    /*
     * We put the ResultRelInfo in the es_opened_result_relations list, even
     * though we don't populate the es_result_relations array.  That's a bit
     * bogus, but it's enough to make ExecGetTriggerResultRel() find them.
     *
     * ExecOpenIndices() is not called here either, each execution path doing
     * an apply operation being responsible for that.
     */
    estate->es_opened_result_relations =
        lappend(estate->es_opened_result_relations, resultRelInfo);
 
    estate->es_output_cid = GetCurrentCommandId(true);
 
    /* Prepare to catch AFTER triggers. */
    AfterTriggerBeginQuery();
 
    /* other fields of edata remain NULL for now */
 
    return edata;
}
 
/*
 * Finish any operations related to the executor state created by
 * create_edata_for_relation().
 */
static void
finish_edata(ApplyExecutionData *edata)
{
    EState     *estate = edata->estate;
 
    /* Handle any queued AFTER triggers. */
    AfterTriggerEndQuery(estate);
 
    /* Shut down tuple routing, if any was done. */
    if (edata->proute)
        ExecCleanupTupleRouting(edata->mtstate, edata->proute);
 
    /*
     * Cleanup.  It might seem that we should call ExecCloseResultRelations()
     * here, but we intentionally don't.  It would close the rel we added to
     * es_opened_result_relations above, which is wrong because we took no
     * corresponding refcount.  We rely on ExecCleanupTupleRouting() to close
     * any other relations opened during execution.
     */
    ExecResetTupleTable(estate->es_tupleTable, false);
    FreeExecutorState(estate);
    pfree(edata);
}
 
/*
 * Executes default values for columns for which we can't map to remote
 * relation columns.
 *
 * This allows us to support tables which have more columns on the downstream
 * than on the upstream.
 */
static void
slot_fill_defaults(LogicalRepRelMapEntry *rel, EState *estate,
                   TupleTableSlot *slot)
{
    TupleDesc   desc = RelationGetDescr(rel->localrel);
    int         num_phys_attrs = desc->natts;
    int         i;
    int         attnum,
                num_defaults = 0;
    int        *defmap;
    ExprState **defexprs;
    ExprContext *econtext;
 
    econtext = GetPerTupleExprContext(estate);
 
    /* We got all the data via replication, no need to evaluate anything. */
    if (num_phys_attrs == rel->remoterel.natts)
        return;
 
    defmap = (int *) palloc(num_phys_attrs * sizeof(int));
    defexprs = (ExprState **) palloc(num_phys_attrs * sizeof(ExprState *));
 
    Assert(rel->attrmap->maplen == num_phys_attrs);
    for (attnum = 0; attnum < num_phys_attrs; attnum++)
    {
        Expr       *defexpr;
 
        if (TupleDescAttr(desc, attnum)->attisdropped || TupleDescAttr(desc, attnum)->attgenerated)
            continue;
 
        if (rel->attrmap->attnums[attnum] >= 0)
            continue;
 
        defexpr = (Expr *) build_column_default(rel->localrel, attnum + 1);
 
        if (defexpr != NULL)
        {
            /* Run the expression through planner */
            defexpr = expression_planner(defexpr);
 
            /* Initialize executable expression in copycontext */
            defexprs[num_defaults] = ExecInitExpr(defexpr, NULL);
            defmap[num_defaults] = attnum;
            num_defaults++;
        }
    }
 
    for (i = 0; i < num_defaults; i++)
        slot->tts_values[defmap[i]] =
            ExecEvalExpr(defexprs[i], econtext, &slot->tts_isnull[defmap[i]]);
}
 
/*
 * Store tuple data into slot.
 *
 * Incoming data can be either text or binary format.
 */
static void
slot_store_data(TupleTableSlot *slot, LogicalRepRelMapEntry *rel,
                LogicalRepTupleData *tupleData)
{
    int         natts = slot->tts_tupleDescriptor->natts;
    int         i;
 
    ExecClearTuple(slot);
 
    /* Call the "in" function for each non-dropped, non-null attribute */
    Assert(natts == rel->attrmap->maplen);
    for (i = 0; i < natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(slot->tts_tupleDescriptor, i);
        int         remoteattnum = rel->attrmap->attnums[i];
 
        if (!att->attisdropped && remoteattnum >= 0)
        {
            StringInfo  colvalue = &tupleData->colvalues[remoteattnum];
 
            Assert(remoteattnum < tupleData->ncols);
 
            /* Set attnum for error callback */
            apply_error_callback_arg.remote_attnum = remoteattnum;
 
            if (tupleData->colstatus[remoteattnum] == LOGICALREP_COLUMN_TEXT)
            {
                Oid         typinput;
                Oid         typioparam;
 
                getTypeInputInfo(att->atttypid, &typinput, &typioparam);
                slot->tts_values[i] =
                    OidInputFunctionCall(typinput, colvalue->data,
                                         typioparam, att->atttypmod);
                slot->tts_isnull[i] = false;
            }
            else if (tupleData->colstatus[remoteattnum] == LOGICALREP_COLUMN_BINARY)
            {
                Oid         typreceive;
                Oid         typioparam;
 
                /*
                 * In some code paths we may be asked to re-parse the same
                 * tuple data.  Reset the StringInfo's cursor so that works.
                 */
                colvalue->cursor = 0;
 
                getTypeBinaryInputInfo(att->atttypid, &typreceive, &typioparam);
                slot->tts_values[i] =
                    OidReceiveFunctionCall(typreceive, colvalue,
                                           typioparam, att->atttypmod);
 
                /* Trouble if it didn't eat the whole buffer */
                if (colvalue->cursor != colvalue->len)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_BINARY_REPRESENTATION),
                             errmsg("incorrect binary data format in logical replication column %d",
                                    remoteattnum + 1)));
                slot->tts_isnull[i] = false;
            }
            else
            {
                /*
                 * NULL value from remote.  (We don't expect to see
                 * LOGICALREP_COLUMN_UNCHANGED here, but if we do, treat it as
                 * NULL.)
                 */
                slot->tts_values[i] = (Datum) 0;
                slot->tts_isnull[i] = true;
            }
 
            /* Reset attnum for error callback */
            apply_error_callback_arg.remote_attnum = -1;
        }
        else
        {
            /*
             * We assign NULL to dropped attributes and missing values
             * (missing values should be later filled using
             * slot_fill_defaults).
             */
            slot->tts_values[i] = (Datum) 0;
            slot->tts_isnull[i] = true;
        }
    }
 
    ExecStoreVirtualTuple(slot);
}
 
/*
 * Replace updated columns with data from the LogicalRepTupleData struct.
 * This is somewhat similar to heap_modify_tuple but also calls the type
 * input functions on the user data.
 *
 * "slot" is filled with a copy of the tuple in "srcslot", replacing
 * columns provided in "tupleData" and leaving others as-is.
 *
 * Caution: unreplaced pass-by-ref columns in "slot" will point into the
 * storage for "srcslot".  This is OK for current usage, but someday we may
 * need to materialize "slot" at the end to make it independent of "srcslot".
 */
static void
slot_modify_data(TupleTableSlot *slot, TupleTableSlot *srcslot,
                 LogicalRepRelMapEntry *rel,
                 LogicalRepTupleData *tupleData)
{
    int         natts = slot->tts_tupleDescriptor->natts;
    int         i;
 
    /* We'll fill "slot" with a virtual tuple, so we must start with ... */
    ExecClearTuple(slot);
 
    /*
     * Copy all the column data from srcslot, so that we'll have valid values
     * for unreplaced columns.
     */
    Assert(natts == srcslot->tts_tupleDescriptor->natts);
    slot_getallattrs(srcslot);
    memcpy(slot->tts_values, srcslot->tts_values, natts * sizeof(Datum));
    memcpy(slot->tts_isnull, srcslot->tts_isnull, natts * sizeof(bool));
 
    /* Call the "in" function for each replaced attribute */
    Assert(natts == rel->attrmap->maplen);
    for (i = 0; i < natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(slot->tts_tupleDescriptor, i);
        int         remoteattnum = rel->attrmap->attnums[i];
 
        if (remoteattnum < 0)
            continue;
 
        Assert(remoteattnum < tupleData->ncols);
 
        if (tupleData->colstatus[remoteattnum] != LOGICALREP_COLUMN_UNCHANGED)
        {
            StringInfo  colvalue = &tupleData->colvalues[remoteattnum];
 
            /* Set attnum for error callback */
            apply_error_callback_arg.remote_attnum = remoteattnum;
 
            if (tupleData->colstatus[remoteattnum] == LOGICALREP_COLUMN_TEXT)
            {
                Oid         typinput;
                Oid         typioparam;
 
                getTypeInputInfo(att->atttypid, &typinput, &typioparam);
                slot->tts_values[i] =
                    OidInputFunctionCall(typinput, colvalue->data,
                                         typioparam, att->atttypmod);
                slot->tts_isnull[i] = false;
            }
            else if (tupleData->colstatus[remoteattnum] == LOGICALREP_COLUMN_BINARY)
            {
                Oid         typreceive;
                Oid         typioparam;
 
                /*
                 * In some code paths we may be asked to re-parse the same
                 * tuple data.  Reset the StringInfo's cursor so that works.
                 */
                colvalue->cursor = 0;
 
                getTypeBinaryInputInfo(att->atttypid, &typreceive, &typioparam);
                slot->tts_values[i] =
                    OidReceiveFunctionCall(typreceive, colvalue,
                                           typioparam, att->atttypmod);
 
                /* Trouble if it didn't eat the whole buffer */
                if (colvalue->cursor != colvalue->len)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_BINARY_REPRESENTATION),
                             errmsg("incorrect binary data format in logical replication column %d",
                                    remoteattnum + 1)));
                slot->tts_isnull[i] = false;
            }
            else
            {
                /* must be LOGICALREP_COLUMN_NULL */
                slot->tts_values[i] = (Datum) 0;
                slot->tts_isnull[i] = true;
            }
 
            /* Reset attnum for error callback */
            apply_error_callback_arg.remote_attnum = -1;
        }
    }
 
    /* And finally, declare that "slot" contains a valid virtual tuple */
    ExecStoreVirtualTuple(slot);
}
 
/*
 * Handle BEGIN message.
 */
static void
apply_handle_begin(StringInfo s)
{
    LogicalRepBeginData begin_data;
 
    /* There must not be an active streaming transaction. */
    Assert(!TransactionIdIsValid(stream_xid));
 
    logicalrep_read_begin(s, &begin_data);
    set_apply_error_context_xact(begin_data.xid, begin_data.final_lsn);
 
    remote_final_lsn = begin_data.final_lsn;
 
    maybe_start_skipping_changes(begin_data.final_lsn);
 
    in_remote_transaction = true;
 
    pgstat_report_activity(STATE_RUNNING, NULL);
}
 
/*
 * Handle COMMIT message.
 *
 * TODO, support tracking of multiple origins
 */
static void
apply_handle_commit(StringInfo s)
{
    LogicalRepCommitData commit_data;
 
    logicalrep_read_commit(s, &commit_data);
 
    if (commit_data.commit_lsn != remote_final_lsn)
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("incorrect commit LSN %X/%08X in commit message (expected %X/%08X)",
                                 LSN_FORMAT_ARGS(commit_data.commit_lsn),
                                 LSN_FORMAT_ARGS(remote_final_lsn))));
 
    apply_handle_commit_internal(&commit_data);
 
    /* Process any tables that are being synchronized in parallel. */
    process_syncing_tables(commit_data.end_lsn);
 
    pgstat_report_activity(STATE_IDLE, NULL);
    reset_apply_error_context_info();
}
 
/*
 * Handle BEGIN PREPARE message.
 */
static void
apply_handle_begin_prepare(StringInfo s)
{
    LogicalRepPreparedTxnData begin_data;
 
    /* Tablesync should never receive prepare. */
    if (am_tablesync_worker())
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("tablesync worker received a BEGIN PREPARE message")));
 
    /* There must not be an active streaming transaction. */
    Assert(!TransactionIdIsValid(stream_xid));
 
    logicalrep_read_begin_prepare(s, &begin_data);
    set_apply_error_context_xact(begin_data.xid, begin_data.prepare_lsn);
 
    remote_final_lsn = begin_data.prepare_lsn;
 
    maybe_start_skipping_changes(begin_data.prepare_lsn);
 
    in_remote_transaction = true;
 
    pgstat_report_activity(STATE_RUNNING, NULL);
}
 
/*
 * Common function to prepare the GID.
 */
static void
apply_handle_prepare_internal(LogicalRepPreparedTxnData *prepare_data)
{
    char        gid[GIDSIZE];
 
    /*
     * Compute unique GID for two_phase transactions. We don't use GID of
     * prepared transaction sent by server as that can lead to deadlock when
     * we have multiple subscriptions from same node point to publications on
     * the same node. See comments atop worker.c
     */
    TwoPhaseTransactionGid(MySubscription->oid, prepare_data->xid,
                           gid, sizeof(gid));
 
    /*
     * BeginTransactionBlock is necessary to balance the EndTransactionBlock
     * called within the PrepareTransactionBlock below.
     */
    if (!IsTransactionBlock())
    {
        BeginTransactionBlock();
        CommitTransactionCommand(); /* Completes the preceding Begin command. */
    }
 
    /*
     * Update origin state so we can restart streaming from correct position
     * in case of crash.
     */
    replorigin_session_origin_lsn = prepare_data->end_lsn;
    replorigin_session_origin_timestamp = prepare_data->prepare_time;
 
    PrepareTransactionBlock(gid);
}
 
/*
 * Handle PREPARE message.
 */
static void
apply_handle_prepare(StringInfo s)
{
    LogicalRepPreparedTxnData prepare_data;
 
    logicalrep_read_prepare(s, &prepare_data);
 
    if (prepare_data.prepare_lsn != remote_final_lsn)
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("incorrect prepare LSN %X/%08X in prepare message (expected %X/%08X)",
                                 LSN_FORMAT_ARGS(prepare_data.prepare_lsn),
                                 LSN_FORMAT_ARGS(remote_final_lsn))));
 
    /*
     * Unlike commit, here, we always prepare the transaction even though no
     * change has happened in this transaction or all changes are skipped. It
     * is done this way because at commit prepared time, we won't know whether
     * we have skipped preparing a transaction because of those reasons.
     *
     * XXX, We can optimize such that at commit prepared time, we first check
     * whether we have prepared the transaction or not but that doesn't seem
     * worthwhile because such cases shouldn't be common.
     */
    begin_replication_step();
 
    apply_handle_prepare_internal(&prepare_data);
 
    end_replication_step();
    CommitTransactionCommand();
    pgstat_report_stat(false);
 
    /*
     * It is okay not to set the local_end LSN for the prepare because we
     * always flush the prepare record. So, we can send the acknowledgment of
     * the remote_end LSN as soon as prepare is finished.
     *
     * XXX For the sake of consistency with commit, we could have set it with
     * the LSN of prepare but as of now we don't track that value similar to
     * XactLastCommitEnd, and adding it for this purpose doesn't seems worth
     * it.
     */
    store_flush_position(prepare_data.end_lsn, InvalidXLogRecPtr);
 
    in_remote_transaction = false;
 
    /* Process any tables that are being synchronized in parallel. */
    process_syncing_tables(prepare_data.end_lsn);
 
    /*
     * Since we have already prepared the transaction, in a case where the
     * server crashes before clearing the subskiplsn, it will be left but the
     * transaction won't be resent. But that's okay because it's a rare case
     * and the subskiplsn will be cleared when finishing the next transaction.
     */
    stop_skipping_changes();
    clear_subscription_skip_lsn(prepare_data.prepare_lsn);
 
    pgstat_report_activity(STATE_IDLE, NULL);
    reset_apply_error_context_info();
}
 
/*
 * Handle a COMMIT PREPARED of a previously PREPARED transaction.
 *
 * Note that we don't need to wait here if the transaction was prepared in a
 * parallel apply worker. In that case, we have already waited for the prepare
 * to finish in apply_handle_stream_prepare() which will ensure all the
 * operations in that transaction have happened in the subscriber, so no
 * concurrent transaction can cause deadlock or transaction dependency issues.
 */
static void
apply_handle_commit_prepared(StringInfo s)
{
    LogicalRepCommitPreparedTxnData prepare_data;
    char        gid[GIDSIZE];
 
    logicalrep_read_commit_prepared(s, &prepare_data);
    set_apply_error_context_xact(prepare_data.xid, prepare_data.commit_lsn);
 
    /* Compute GID for two_phase transactions. */
    TwoPhaseTransactionGid(MySubscription->oid, prepare_data.xid,
                           gid, sizeof(gid));
 
    /* There is no transaction when COMMIT PREPARED is called */
    begin_replication_step();
 
    /*
     * Update origin state so we can restart streaming from correct position
     * in case of crash.
     */
    replorigin_session_origin_lsn = prepare_data.end_lsn;
    replorigin_session_origin_timestamp = prepare_data.commit_time;
 
    FinishPreparedTransaction(gid, true);
    end_replication_step();
    CommitTransactionCommand();
    pgstat_report_stat(false);
 
    store_flush_position(prepare_data.end_lsn, XactLastCommitEnd);
    in_remote_transaction = false;
 
    /* Process any tables that are being synchronized in parallel. */
    process_syncing_tables(prepare_data.end_lsn);
 
    clear_subscription_skip_lsn(prepare_data.end_lsn);
 
    pgstat_report_activity(STATE_IDLE, NULL);
    reset_apply_error_context_info();
}
 
/*
 * Handle a ROLLBACK PREPARED of a previously PREPARED TRANSACTION.
 *
 * Note that we don't need to wait here if the transaction was prepared in a
 * parallel apply worker. In that case, we have already waited for the prepare
 * to finish in apply_handle_stream_prepare() which will ensure all the
 * operations in that transaction have happened in the subscriber, so no
 * concurrent transaction can cause deadlock or transaction dependency issues.
 */
static void
apply_handle_rollback_prepared(StringInfo s)
{
    LogicalRepRollbackPreparedTxnData rollback_data;
    char        gid[GIDSIZE];
 
    logicalrep_read_rollback_prepared(s, &rollback_data);
    set_apply_error_context_xact(rollback_data.xid, rollback_data.rollback_end_lsn);
 
    /* Compute GID for two_phase transactions. */
    TwoPhaseTransactionGid(MySubscription->oid, rollback_data.xid,
                           gid, sizeof(gid));
 
    /*
     * It is possible that we haven't received prepare because it occurred
     * before walsender reached a consistent point or the two_phase was still
     * not enabled by that time, so in such cases, we need to skip rollback
     * prepared.
     */
    if (LookupGXact(gid, rollback_data.prepare_end_lsn,
                    rollback_data.prepare_time))
    {
        /*
         * Update origin state so we can restart streaming from correct
         * position in case of crash.
         */
        replorigin_session_origin_lsn = rollback_data.rollback_end_lsn;
        replorigin_session_origin_timestamp = rollback_data.rollback_time;
 
        /* There is no transaction when ABORT/ROLLBACK PREPARED is called */
        begin_replication_step();
        FinishPreparedTransaction(gid, false);
        end_replication_step();
        CommitTransactionCommand();
 
        clear_subscription_skip_lsn(rollback_data.rollback_end_lsn);
    }
 
    pgstat_report_stat(false);
 
    /*
     * It is okay not to set the local_end LSN for the rollback of prepared
     * transaction because we always flush the WAL record for it. See
     * apply_handle_prepare.
     */
    store_flush_position(rollback_data.rollback_end_lsn, InvalidXLogRecPtr);
    in_remote_transaction = false;
 
    /* Process any tables that are being synchronized in parallel. */
    process_syncing_tables(rollback_data.rollback_end_lsn);
 
    pgstat_report_activity(STATE_IDLE, NULL);
    reset_apply_error_context_info();
}
 
/*
 * Handle STREAM PREPARE.
 */
static void
apply_handle_stream_prepare(StringInfo s)
{
    LogicalRepPreparedTxnData prepare_data;
    ParallelApplyWorkerInfo *winfo;
    TransApplyAction apply_action;
 
    /* Save the message before it is consumed. */
    StringInfoData original_msg = *s;
 
    if (in_streamed_transaction)
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("STREAM PREPARE message without STREAM STOP")));
 
    /* Tablesync should never receive prepare. */
    if (am_tablesync_worker())
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("tablesync worker received a STREAM PREPARE message")));
 
    logicalrep_read_stream_prepare(s, &prepare_data);
    set_apply_error_context_xact(prepare_data.xid, prepare_data.prepare_lsn);
 
    apply_action = get_transaction_apply_action(prepare_data.xid, &winfo);
 
    switch (apply_action)
    {
        case TRANS_LEADER_APPLY:
 
            /*
             * The transaction has been serialized to file, so replay all the
             * spooled operations.
             */
            apply_spooled_messages(MyLogicalRepWorker->stream_fileset,
                                   prepare_data.xid, prepare_data.prepare_lsn);
 
            /* Mark the transaction as prepared. */
            apply_handle_prepare_internal(&prepare_data);
 
            CommitTransactionCommand();
 
            /*
             * It is okay not to set the local_end LSN for the prepare because
             * we always flush the prepare record. See apply_handle_prepare.
             */
            store_flush_position(prepare_data.end_lsn, InvalidXLogRecPtr);
 
            in_remote_transaction = false;
 
            /* Unlink the files with serialized changes and subxact info. */
            stream_cleanup_files(MyLogicalRepWorker->subid, prepare_data.xid);
 
            elog(DEBUG1, "finished processing the STREAM PREPARE command");
            break;
 
        case TRANS_LEADER_SEND_TO_PARALLEL:
            Assert(winfo);
 
            if (pa_send_data(winfo, s->len, s->data))
            {
                /* Finish processing the streaming transaction. */
                pa_xact_finish(winfo, prepare_data.end_lsn);
                break;
            }
 
            /*
             * Switch to serialize mode when we are not able to send the
             * change to parallel apply worker.
             */
            pa_switch_to_partial_serialize(winfo, true);
 
            /* fall through */
        case TRANS_LEADER_PARTIAL_SERIALIZE:
            Assert(winfo);
 
            stream_open_and_write_change(prepare_data.xid,
                                         LOGICAL_REP_MSG_STREAM_PREPARE,
                                         &original_msg);
 
            pa_set_fileset_state(winfo->shared, FS_SERIALIZE_DONE);
 
            /* Finish processing the streaming transaction. */
            pa_xact_finish(winfo, prepare_data.end_lsn);
            break;
 
        case TRANS_PARALLEL_APPLY:
 
            /*
             * If the parallel apply worker is applying spooled messages then
             * close the file before preparing.
             */
            if (stream_fd)
                stream_close_file();
 
            begin_replication_step();
 
            /* Mark the transaction as prepared. */
            apply_handle_prepare_internal(&prepare_data);
 
            end_replication_step();
 
            CommitTransactionCommand();
 
            /*
             * It is okay not to set the local_end LSN for the prepare because
             * we always flush the prepare record. See apply_handle_prepare.
             */
            MyParallelShared->last_commit_end = InvalidXLogRecPtr;
 
            pa_set_xact_state(MyParallelShared, PARALLEL_TRANS_FINISHED);
            pa_unlock_transaction(MyParallelShared->xid, AccessExclusiveLock);
 
            pa_reset_subtrans();
 
            elog(DEBUG1, "finished processing the STREAM PREPARE command");
            break;
 
        default:
            elog(ERROR, "unexpected apply action: %d", (int) apply_action);
            break;
    }
 
    pgstat_report_stat(false);
 
    /* Process any tables that are being synchronized in parallel. */
    process_syncing_tables(prepare_data.end_lsn);
 
    /*
     * Similar to prepare case, the subskiplsn could be left in a case of
     * server crash but it's okay. See the comments in apply_handle_prepare().
     */
    stop_skipping_changes();
    clear_subscription_skip_lsn(prepare_data.prepare_lsn);
 
    pgstat_report_activity(STATE_IDLE, NULL);
 
    reset_apply_error_context_info();
}
 
/*
 * Handle ORIGIN message.
 *
 * TODO, support tracking of multiple origins
 */
static void
apply_handle_origin(StringInfo s)
{
    /*
     * ORIGIN message can only come inside streaming transaction or inside
     * remote transaction and before any actual writes.
     */
    if (!in_streamed_transaction &&
        (!in_remote_transaction ||
         (IsTransactionState() && !am_tablesync_worker())))
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("ORIGIN message sent out of order")));
}
 
/*
 * Initialize fileset (if not already done).
 *
 * Create a new file when first_segment is true, otherwise open the existing
 * file.
 */
void
stream_start_internal(TransactionId xid, bool first_segment)
{
    begin_replication_step();
 
    /*
     * Initialize the worker's stream_fileset if we haven't yet. This will be
     * used for the entire duration of the worker so create it in a permanent
     * context. We create this on the very first streaming message from any
     * transaction and then use it for this and other streaming transactions.
     * Now, we could create a fileset at the start of the worker as well but
     * then we won't be sure that it will ever be used.
     */
    if (!MyLogicalRepWorker->stream_fileset)
    {
        MemoryContext oldctx;
 
        oldctx = MemoryContextSwitchTo(ApplyContext);
 
        MyLogicalRepWorker->stream_fileset = palloc(sizeof(FileSet));
        FileSetInit(MyLogicalRepWorker->stream_fileset);
 
        MemoryContextSwitchTo(oldctx);
    }
 
    /* Open the spool file for this transaction. */
    stream_open_file(MyLogicalRepWorker->subid, xid, first_segment);
 
    /* If this is not the first segment, open existing subxact file. */
    if (!first_segment)
        subxact_info_read(MyLogicalRepWorker->subid, xid);
 
    end_replication_step();
}
 
/*
 * Handle STREAM START message.
 */
static void
apply_handle_stream_start(StringInfo s)
{
    bool        first_segment;
    ParallelApplyWorkerInfo *winfo;
    TransApplyAction apply_action;
 
    /* Save the message before it is consumed. */
    StringInfoData original_msg = *s;
 
    if (in_streamed_transaction)
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("duplicate STREAM START message")));
 
    /* There must not be an active streaming transaction. */
    Assert(!TransactionIdIsValid(stream_xid));
 
    /* notify handle methods we're processing a remote transaction */
    in_streamed_transaction = true;
 
    /* extract XID of the top-level transaction */
    stream_xid = logicalrep_read_stream_start(s, &first_segment);
 
    if (!TransactionIdIsValid(stream_xid))
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("invalid transaction ID in streamed replication transaction")));
 
    set_apply_error_context_xact(stream_xid, InvalidXLogRecPtr);
 
    /* Try to allocate a worker for the streaming transaction. */
    if (first_segment)
        pa_allocate_worker(stream_xid);
 
    apply_action = get_transaction_apply_action(stream_xid, &winfo);
 
    switch (apply_action)
    {
        case TRANS_LEADER_SERIALIZE:
 
            /*
             * Function stream_start_internal starts a transaction. This
             * transaction will be committed on the stream stop unless it is a
             * tablesync worker in which case it will be committed after
             * processing all the messages. We need this transaction for
             * handling the BufFile, used for serializing the streaming data
             * and subxact info.
             */
            stream_start_internal(stream_xid, first_segment);
            break;
 
        case TRANS_LEADER_SEND_TO_PARALLEL:
            Assert(winfo);
 
            /*
             * Once we start serializing the changes, the parallel apply
             * worker will wait for the leader to release the stream lock
             * until the end of the transaction. So, we don't need to release
             * the lock or increment the stream count in that case.
             */
            if (pa_send_data(winfo, s->len, s->data))
            {
                /*
                 * Unlock the shared object lock so that the parallel apply
                 * worker can continue to receive changes.
                 */
                if (!first_segment)
                    pa_unlock_stream(winfo->shared->xid, AccessExclusiveLock);
 
                /*
                 * Increment the number of streaming blocks waiting to be
                 * processed by parallel apply worker.
                 */
                pg_atomic_add_fetch_u32(&winfo->shared->pending_stream_count, 1);
 
                /* Cache the parallel apply worker for this transaction. */
                pa_set_stream_apply_worker(winfo);
                break;
            }
 
            /*
             * Switch to serialize mode when we are not able to send the
             * change to parallel apply worker.
             */
            pa_switch_to_partial_serialize(winfo, !first_segment);
 
            /* fall through */
        case TRANS_LEADER_PARTIAL_SERIALIZE:
            Assert(winfo);
 
            /*
             * Open the spool file unless it was already opened when switching
             * to serialize mode. The transaction started in
             * stream_start_internal will be committed on the stream stop.
             */
            if (apply_action != TRANS_LEADER_SEND_TO_PARALLEL)
                stream_start_internal(stream_xid, first_segment);
 
            stream_write_change(LOGICAL_REP_MSG_STREAM_START, &original_msg);
 
            /* Cache the parallel apply worker for this transaction. */
            pa_set_stream_apply_worker(winfo);
            break;
 
        case TRANS_PARALLEL_APPLY:
            if (first_segment)
            {
                /* Hold the lock until the end of the transaction. */
                pa_lock_transaction(MyParallelShared->xid, AccessExclusiveLock);
                pa_set_xact_state(MyParallelShared, PARALLEL_TRANS_STARTED);
 
                /*
                 * Signal the leader apply worker, as it may be waiting for
                 * us.
                 */
                logicalrep_worker_wakeup(MyLogicalRepWorker->subid, InvalidOid);
            }
 
            parallel_stream_nchanges = 0;
            break;
 
        default:
            elog(ERROR, "unexpected apply action: %d", (int) apply_action);
            break;
    }
 
    pgstat_report_activity(STATE_RUNNING, NULL);
}
 
/*
 * Update the information about subxacts and close the file.
 *
 * This function should be called when the stream_start_internal function has
 * been called.
 */
void
stream_stop_internal(TransactionId xid)
{
    /*
     * Serialize information about subxacts for the toplevel transaction, then
     * close the stream messages spool file.
     */
    subxact_info_write(MyLogicalRepWorker->subid, xid);
    stream_close_file();
 
    /* We must be in a valid transaction state */
    Assert(IsTransactionState());
 
    /* Commit the per-stream transaction */
    CommitTransactionCommand();
 
    /* Reset per-stream context */
    MemoryContextReset(LogicalStreamingContext);
}
 
/*
 * Handle STREAM STOP message.
 */
static void
apply_handle_stream_stop(StringInfo s)
{
    ParallelApplyWorkerInfo *winfo;
    TransApplyAction apply_action;
 
    if (!in_streamed_transaction)
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("STREAM STOP message without STREAM START")));
 
    apply_action = get_transaction_apply_action(stream_xid, &winfo);
 
    switch (apply_action)
    {
        case TRANS_LEADER_SERIALIZE:
            stream_stop_internal(stream_xid);
            break;
 
        case TRANS_LEADER_SEND_TO_PARALLEL:
            Assert(winfo);
 
            /*
             * Lock before sending the STREAM_STOP message so that the leader
             * can hold the lock first and the parallel apply worker will wait
             * for leader to release the lock. See Locking Considerations atop
             * applyparallelworker.c.
             */
            pa_lock_stream(winfo->shared->xid, AccessExclusiveLock);
 
            if (pa_send_data(winfo, s->len, s->data))
            {
                pa_set_stream_apply_worker(NULL);
                break;
            }
 
            /*
             * Switch to serialize mode when we are not able to send the
             * change to parallel apply worker.
             */
            pa_switch_to_partial_serialize(winfo, true);
 
            /* fall through */
        case TRANS_LEADER_PARTIAL_SERIALIZE:
            stream_write_change(LOGICAL_REP_MSG_STREAM_STOP, s);
            stream_stop_internal(stream_xid);
            pa_set_stream_apply_worker(NULL);
            break;
 
        case TRANS_PARALLEL_APPLY:
            elog(DEBUG1, "applied %u changes in the streaming chunk",
                 parallel_stream_nchanges);
 
            /*
             * By the time parallel apply worker is processing the changes in
             * the current streaming block, the leader apply worker may have
             * sent multiple streaming blocks. This can lead to parallel apply
             * worker start waiting even when there are more chunk of streams
             * in the queue. So, try to lock only if there is no message left
             * in the queue. See Locking Considerations atop
             * applyparallelworker.c.
             *
             * Note that here we have a race condition where we can start
             * waiting even when there are pending streaming chunks. This can
             * happen if the leader sends another streaming block and acquires
             * the stream lock again after the parallel apply worker checks
             * that there is no pending streaming block and before it actually
             * starts waiting on a lock. We can handle this case by not
             * allowing the leader to increment the stream block count during
             * the time parallel apply worker acquires the lock but it is not
             * clear whether that is worth the complexity.
             *
             * Now, if this missed chunk contains rollback to savepoint, then
             * there is a risk of deadlock which probably shouldn't happen
             * after restart.
             */
            pa_decr_and_wait_stream_block();
            break;
 
        default:
            elog(ERROR, "unexpected apply action: %d", (int) apply_action);
            break;
    }
 
    in_streamed_transaction = false;
    stream_xid = InvalidTransactionId;
 
    /*
     * The parallel apply worker could be in a transaction in which case we
     * need to report the state as STATE_IDLEINTRANSACTION.
     */
    if (IsTransactionOrTransactionBlock())
        pgstat_report_activity(STATE_IDLEINTRANSACTION, NULL);
    else
        pgstat_report_activity(STATE_IDLE, NULL);
 
    reset_apply_error_context_info();
}
 
/*
 * Helper function to handle STREAM ABORT message when the transaction was
 * serialized to file.
 */
static void
stream_abort_internal(TransactionId xid, TransactionId subxid)
{
    /*
     * If the two XIDs are the same, it's in fact abort of toplevel xact, so
     * just delete the files with serialized info.
     */
    if (xid == subxid)
        stream_cleanup_files(MyLogicalRepWorker->subid, xid);
    else
    {
        /*
         * OK, so it's a subxact. We need to read the subxact file for the
         * toplevel transaction, determine the offset tracked for the subxact,
         * and truncate the file with changes. We also remove the subxacts
         * with higher offsets (or rather higher XIDs).
         *
         * We intentionally scan the array from the tail, because we're likely
         * aborting a change for the most recent subtransactions.
         *
         * We can't use the binary search here as subxact XIDs won't
         * necessarily arrive in sorted order, consider the case where we have
         * released the savepoint for multiple subtransactions and then
         * performed rollback to savepoint for one of the earlier
         * sub-transaction.
         */
        int64       i;
        int64       subidx;
        BufFile    *fd;
        bool        found = false;
        char        path[MAXPGPATH];
 
        subidx = -1;
        begin_replication_step();
        subxact_info_read(MyLogicalRepWorker->subid, xid);
 
        for (i = subxact_data.nsubxacts; i > 0; i--)
        {
            if (subxact_data.subxacts[i - 1].xid == subxid)
            {
                subidx = (i - 1);
                found = true;
                break;
            }
        }
 
        /*
         * If it's an empty sub-transaction then we will not find the subxid
         * here so just cleanup the subxact info and return.
         */
        if (!found)
        {
            /* Cleanup the subxact info */
            cleanup_subxact_info();
            end_replication_step();
            CommitTransactionCommand();
            return;
        }
 
        /* open the changes file */
        changes_filename(path, MyLogicalRepWorker->subid, xid);
        fd = BufFileOpenFileSet(MyLogicalRepWorker->stream_fileset, path,
                                O_RDWR, false);
 
        /* OK, truncate the file at the right offset */
        BufFileTruncateFileSet(fd, subxact_data.subxacts[subidx].fileno,
                               subxact_data.subxacts[subidx].offset);
        BufFileClose(fd);
 
        /* discard the subxacts added later */
        subxact_data.nsubxacts = subidx;
 
        /* write the updated subxact list */
        subxact_info_write(MyLogicalRepWorker->subid, xid);
 
        end_replication_step();
        CommitTransactionCommand();
    }
}
 
/*
 * Handle STREAM ABORT message.
 */
static void
apply_handle_stream_abort(StringInfo s)
{
    TransactionId xid;
    TransactionId subxid;
    LogicalRepStreamAbortData abort_data;
    ParallelApplyWorkerInfo *winfo;
    TransApplyAction apply_action;
 
    /* Save the message before it is consumed. */
    StringInfoData original_msg = *s;
    bool        toplevel_xact;
 
    if (in_streamed_transaction)
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("STREAM ABORT message without STREAM STOP")));
 
    /* We receive abort information only when we can apply in parallel. */
    logicalrep_read_stream_abort(s, &abort_data,
                                 MyLogicalRepWorker->parallel_apply);
 
    xid = abort_data.xid;
    subxid = abort_data.subxid;
    toplevel_xact = (xid == subxid);
 
    set_apply_error_context_xact(subxid, abort_data.abort_lsn);
 
    apply_action = get_transaction_apply_action(xid, &winfo);
 
    switch (apply_action)
    {
        case TRANS_LEADER_APPLY:
 
            /*
             * We are in the leader apply worker and the transaction has been
             * serialized to file.
             */
            stream_abort_internal(xid, subxid);
 
            elog(DEBUG1, "finished processing the STREAM ABORT command");
            break;
 
        case TRANS_LEADER_SEND_TO_PARALLEL:
            Assert(winfo);
 
            /*
             * For the case of aborting the subtransaction, we increment the
             * number of streaming blocks and take the lock again before
             * sending the STREAM_ABORT to ensure that the parallel apply
             * worker will wait on the lock for the next set of changes after
             * processing the STREAM_ABORT message if it is not already
             * waiting for STREAM_STOP message.
             *
             * It is important to perform this locking before sending the
             * STREAM_ABORT message so that the leader can hold the lock first
             * and the parallel apply worker will wait for the leader to
             * release the lock. This is the same as what we do in
             * apply_handle_stream_stop. See Locking Considerations atop
             * applyparallelworker.c.
             */
            if (!toplevel_xact)
            {
                pa_unlock_stream(xid, AccessExclusiveLock);
                pg_atomic_add_fetch_u32(&winfo->shared->pending_stream_count, 1);
                pa_lock_stream(xid, AccessExclusiveLock);
            }
 
            if (pa_send_data(winfo, s->len, s->data))
            {
                /*
                 * Unlike STREAM_COMMIT and STREAM_PREPARE, we don't need to
                 * wait here for the parallel apply worker to finish as that
                 * is not required to maintain the commit order and won't have
                 * the risk of failures due to transaction dependencies and
                 * deadlocks. However, it is possible that before the parallel
                 * worker finishes and we clear the worker info, the xid
                 * wraparound happens on the upstream and a new transaction
                 * with the same xid can appear and that can lead to duplicate
                 * entries in ParallelApplyTxnHash. Yet another problem could
                 * be that we may have serialized the changes in partial
                 * serialize mode and the file containing xact changes may
                 * already exist, and after xid wraparound trying to create
                 * the file for the same xid can lead to an error. To avoid
                 * these problems, we decide to wait for the aborts to finish.
                 *
                 * Note, it is okay to not update the flush location position
                 * for aborts as in worst case that means such a transaction
                 * won't be sent again after restart.
                 */
                if (toplevel_xact)
                    pa_xact_finish(winfo, InvalidXLogRecPtr);
 
                break;
            }
 
            /*
             * Switch to serialize mode when we are not able to send the
             * change to parallel apply worker.
             */
            pa_switch_to_partial_serialize(winfo, true);
 
            /* fall through */
        case TRANS_LEADER_PARTIAL_SERIALIZE:
            Assert(winfo);
 
            /*
             * Parallel apply worker might have applied some changes, so write
             * the STREAM_ABORT message so that it can rollback the
             * subtransaction if needed.
             */
            stream_open_and_write_change(xid, LOGICAL_REP_MSG_STREAM_ABORT,
                                         &original_msg);
 
            if (toplevel_xact)
            {
                pa_set_fileset_state(winfo->shared, FS_SERIALIZE_DONE);
                pa_xact_finish(winfo, InvalidXLogRecPtr);
            }
            break;
 
        case TRANS_PARALLEL_APPLY:
 
            /*
             * If the parallel apply worker is applying spooled messages then
             * close the file before aborting.
             */
            if (toplevel_xact && stream_fd)
                stream_close_file();
 
            pa_stream_abort(&abort_data);
 
            /*
             * We need to wait after processing rollback to savepoint for the
             * next set of changes.
             *
             * We have a race condition here due to which we can start waiting
             * here when there are more chunk of streams in the queue. See
             * apply_handle_stream_stop.
             */
            if (!toplevel_xact)
                pa_decr_and_wait_stream_block();
 
            elog(DEBUG1, "finished processing the STREAM ABORT command");
            break;
 
        default:
            elog(ERROR, "unexpected apply action: %d", (int) apply_action);
            break;
    }
 
    reset_apply_error_context_info();
}
 
/*
 * Ensure that the passed location is fileset's end.
 */
static void
ensure_last_message(FileSet *stream_fileset, TransactionId xid, int fileno,
                    off_t offset)
{
    char        path[MAXPGPATH];
    BufFile    *fd;
    int         last_fileno;
    off_t       last_offset;
 
    Assert(!IsTransactionState());
 
    begin_replication_step();
 
    changes_filename(path, MyLogicalRepWorker->subid, xid);
 
    fd = BufFileOpenFileSet(stream_fileset, path, O_RDONLY, false);
 
    BufFileSeek(fd, 0, 0, SEEK_END);
    BufFileTell(fd, &last_fileno, &last_offset);
 
    BufFileClose(fd);
 
    end_replication_step();
 
    if (last_fileno != fileno || last_offset != offset)
        elog(ERROR, "unexpected message left in streaming transaction's changes file \"%s\"",
             path);
}
 
/*
 * Common spoolfile processing.
 */
void
apply_spooled_messages(FileSet *stream_fileset, TransactionId xid,
                       XLogRecPtr lsn)
{
    int         nchanges;
    char        path[MAXPGPATH];
    char       *buffer = NULL;
    MemoryContext oldcxt;
    ResourceOwner oldowner;
    int         fileno;
    off_t       offset;
 
    if (!am_parallel_apply_worker())
        maybe_start_skipping_changes(lsn);
 
    /* Make sure we have an open transaction */
    begin_replication_step();
 
    /*
     * Allocate file handle and memory required to process all the messages in
     * TopTransactionContext to avoid them getting reset after each message is
     * processed.
     */
    oldcxt = MemoryContextSwitchTo(TopTransactionContext);
 
    /* Open the spool file for the committed/prepared transaction */
    changes_filename(path, MyLogicalRepWorker->subid, xid);
    elog(DEBUG1, "replaying changes from file \"%s\"", path);
 
    /*
     * Make sure the file is owned by the toplevel transaction so that the
     * file will not be accidentally closed when aborting a subtransaction.
     */
    oldowner = CurrentResourceOwner;
    CurrentResourceOwner = TopTransactionResourceOwner;
 
    stream_fd = BufFileOpenFileSet(stream_fileset, path, O_RDONLY, false);
 
    CurrentResourceOwner = oldowner;
 
    buffer = palloc(BLCKSZ);
 
    MemoryContextSwitchTo(oldcxt);
 
    remote_final_lsn = lsn;
 
    /*
     * Make sure the handle apply_dispatch methods are aware we're in a remote
     * transaction.
     */
    in_remote_transaction = true;
    pgstat_report_activity(STATE_RUNNING, NULL);
 
    end_replication_step();
 
    /*
     * Read the entries one by one and pass them through the same logic as in
     * apply_dispatch.
     */
    nchanges = 0;
    while (true)
    {
        StringInfoData s2;
        size_t      nbytes;
        int         len;
 
        CHECK_FOR_INTERRUPTS();
 
        /* read length of the on-disk record */
        nbytes = BufFileReadMaybeEOF(stream_fd, &len, sizeof(len), true);
 
        /* have we reached end of the file? */
        if (nbytes == 0)
            break;
 
        /* do we have a correct length? */
        if (len <= 0)
            elog(ERROR, "incorrect length %d in streaming transaction's changes file \"%s\"",
                 len, path);
 
        /* make sure we have sufficiently large buffer */
        buffer = repalloc(buffer, len);
 
        /* and finally read the data into the buffer */
        BufFileReadExact(stream_fd, buffer, len);
 
        BufFileTell(stream_fd, &fileno, &offset);
 
        /* init a stringinfo using the buffer and call apply_dispatch */
        initReadOnlyStringInfo(&s2, buffer, len);
 
        /* Ensure we are reading the data into our memory context. */
        oldcxt = MemoryContextSwitchTo(ApplyMessageContext);
 
        apply_dispatch(&s2);
 
        MemoryContextReset(ApplyMessageContext);
 
        MemoryContextSwitchTo(oldcxt);
 
        nchanges++;
 
        /*
         * It is possible the file has been closed because we have processed
         * the transaction end message like stream_commit in which case that
         * must be the last message.
         */
        if (!stream_fd)
        {
            ensure_last_message(stream_fileset, xid, fileno, offset);
            break;
        }
 
        if (nchanges % 1000 == 0)
            elog(DEBUG1, "replayed %d changes from file \"%s\"",
                 nchanges, path);
    }
 
    if (stream_fd)
        stream_close_file();
 
    elog(DEBUG1, "replayed %d (all) changes from file \"%s\"",
         nchanges, path);
 
    return;
}
 
/*
 * Handle STREAM COMMIT message.
 */
static void
apply_handle_stream_commit(StringInfo s)
{
    TransactionId xid;
    LogicalRepCommitData commit_data;
    ParallelApplyWorkerInfo *winfo;
    TransApplyAction apply_action;
 
    /* Save the message before it is consumed. */
    StringInfoData original_msg = *s;
 
    if (in_streamed_transaction)
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg_internal("STREAM COMMIT message without STREAM STOP")));
 
    xid = logicalrep_read_stream_commit(s, &commit_data);
    set_apply_error_context_xact(xid, commit_data.commit_lsn);
 
    apply_action = get_transaction_apply_action(xid, &winfo);
 
    switch (apply_action)
    {
        case TRANS_LEADER_APPLY:
 
            /*
             * The transaction has been serialized to file, so replay all the
             * spooled operations.
             */
            apply_spooled_messages(MyLogicalRepWorker->stream_fileset, xid,
                                   commit_data.commit_lsn);
 
            apply_handle_commit_internal(&commit_data);
 
            /* Unlink the files with serialized changes and subxact info. */
            stream_cleanup_files(MyLogicalRepWorker->subid, xid);
 
            elog(DEBUG1, "finished processing the STREAM COMMIT command");
            break;
 
        case TRANS_LEADER_SEND_TO_PARALLEL:
            Assert(winfo);
 
            if (pa_send_data(winfo, s->len, s->data))
            {
                /* Finish processing the streaming transaction. */
                pa_xact_finish(winfo, commit_data.end_lsn);
                break;
            }
 
            /*
             * Switch to serialize mode when we are not able to send the
             * change to parallel apply worker.
             */
            pa_switch_to_partial_serialize(winfo, true);
 
            /* fall through */
        case TRANS_LEADER_PARTIAL_SERIALIZE:
            Assert(winfo);
 
            stream_open_and_write_change(xid, LOGICAL_REP_MSG_STREAM_COMMIT,
                                         &original_msg);
 
            pa_set_fileset_state(winfo->shared, FS_SERIALIZE_DONE);
 
            /* Finish processing the streaming transaction. */
            pa_xact_finish(winfo, commit_data.end_lsn);
            break;
 
        case TRANS_PARALLEL_APPLY:
 
            /*
             * If the parallel apply worker is applying spooled messages then
             * close the file before committing.
             */
            if (stream_fd)
                stream_close_file();
 
            apply_handle_commit_internal(&commit_data);
 
            MyParallelShared->last_commit_end = XactLastCommitEnd;
 
            /*
             * It is important to set the transaction state as finished before
             * releasing the lock. See pa_wait_for_xact_finish.
             */
            pa_set_xact_state(MyParallelShared, PARALLEL_TRANS_FINISHED);
            pa_unlock_transaction(xid, AccessExclusiveLock);
 
            pa_reset_subtrans();
 
            elog(DEBUG1, "finished processing the STREAM COMMIT command");
            break;
 
        default:
            elog(ERROR, "unexpected apply action: %d", (int) apply_action);
            break;
    }
 
    /* Process any tables that are being synchronized in parallel. */
    process_syncing_tables(commit_data.end_lsn);
 
    pgstat_report_activity(STATE_IDLE, NULL);
 
    reset_apply_error_context_info();
}
 
/*
 * Helper function for apply_handle_commit and apply_handle_stream_commit.
 */
static void
apply_handle_commit_internal(LogicalRepCommitData *commit_data)
{
    if (is_skipping_changes())
    {
        stop_skipping_changes();
 
        /*
         * Start a new transaction to clear the subskiplsn, if not started
         * yet.
         */
        if (!IsTransactionState())
            StartTransactionCommand();
    }
 
    if (IsTransactionState())
    {
        /*
         * The transaction is either non-empty or skipped, so we clear the
         * subskiplsn.
         */
        clear_subscription_skip_lsn(commit_data->commit_lsn);
 
        /*
         * Update origin state so we can restart streaming from correct
         * position in case of crash.
         */
        replorigin_session_origin_lsn = commit_data->end_lsn;
        replorigin_session_origin_timestamp = commit_data->committime;
 
        CommitTransactionCommand();
 
        if (IsTransactionBlock())
        {
            EndTransactionBlock(false);
            CommitTransactionCommand();
        }
 
        pgstat_report_stat(false);
 
        store_flush_position(commit_data->end_lsn, XactLastCommitEnd);
    }
    else
    {
        /* Process any invalidation messages that might have accumulated. */
        AcceptInvalidationMessages();
        maybe_reread_subscription();
    }
 
    in_remote_transaction = false;
}
 
/*
 * Handle RELATION message.
 *
 * Note we don't do validation against local schema here. The validation
 * against local schema is postponed until first change for given relation
 * comes as we only care about it when applying changes for it anyway and we
 * do less locking this way.
 */
static void
apply_handle_relation(StringInfo s)
{
    LogicalRepRelation *rel;
 
    if (handle_streamed_transaction(LOGICAL_REP_MSG_RELATION, s))
        return;
 
    rel = logicalrep_read_rel(s);
    logicalrep_relmap_update(rel);
 
    /* Also reset all entries in the partition map that refer to remoterel. */
    logicalrep_partmap_reset_relmap(rel);
}
 
/*
 * Handle TYPE message.
 *
 * This implementation pays no attention to TYPE messages; we expect the user
 * to have set things up so that the incoming data is acceptable to the input
 * functions for the locally subscribed tables.  Hence, we just read and
 * discard the message.
 */
static void
apply_handle_type(StringInfo s)
{
    LogicalRepTyp typ;
 
    if (handle_streamed_transaction(LOGICAL_REP_MSG_TYPE, s))
        return;
 
    logicalrep_read_typ(s, &typ);
}
 
/*
 * Check that we (the subscription owner) have sufficient privileges on the
 * target relation to perform the given operation.
 */
static void
TargetPrivilegesCheck(Relation rel, AclMode mode)
{
    Oid         relid;
    AclResult   aclresult;
 
    relid = RelationGetRelid(rel);
    aclresult = pg_class_aclcheck(relid, GetUserId(), mode);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult,
                       get_relkind_objtype(rel->rd_rel->relkind),
                       get_rel_name(relid));
 
    /*
     * We lack the infrastructure to honor RLS policies.  It might be possible
     * to add such infrastructure here, but tablesync workers lack it, too, so
     * we don't bother.  RLS does not ordinarily apply to TRUNCATE commands,
     * but it seems dangerous to replicate a TRUNCATE and then refuse to
     * replicate subsequent INSERTs, so we forbid all commands the same.
     */
    if (check_enable_rls(relid, InvalidOid, false) == RLS_ENABLED)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("user \"%s\" cannot replicate into relation with row-level security enabled: \"%s\"",
                        GetUserNameFromId(GetUserId(), true),
                        RelationGetRelationName(rel))));
}
 
/*
 * Handle INSERT message.
 */
 
static void
apply_handle_insert(StringInfo s)
{
    LogicalRepRelMapEntry *rel;
    LogicalRepTupleData newtup;
    LogicalRepRelId relid;
    UserContext ucxt;
    ApplyExecutionData *edata;
    EState     *estate;
    TupleTableSlot *remoteslot;
    MemoryContext oldctx;
    bool        run_as_owner;
 
    /*
     * Quick return if we are skipping data modification changes or handling
     * streamed transactions.
     */
    if (is_skipping_changes() ||
        handle_streamed_transaction(LOGICAL_REP_MSG_INSERT, s))
        return;
 
    begin_replication_step();
 
    relid = logicalrep_read_insert(s, &newtup);
    rel = logicalrep_rel_open(relid, RowExclusiveLock);
    if (!should_apply_changes_for_rel(rel))
    {
        /*
         * The relation can't become interesting in the middle of the
         * transaction so it's safe to unlock it.
         */
        logicalrep_rel_close(rel, RowExclusiveLock);
        end_replication_step();
        return;
    }
 
    /*
     * Make sure that any user-supplied code runs as the table owner, unless
     * the user has opted out of that behavior.
     */
    run_as_owner = MySubscription->runasowner;
    if (!run_as_owner)
        SwitchToUntrustedUser(rel->localrel->rd_rel->relowner, &ucxt);
 
    /* Set relation for error callback */
    apply_error_callback_arg.rel = rel;
 
    /* Initialize the executor state. */
    edata = create_edata_for_relation(rel);
    estate = edata->estate;
    remoteslot = ExecInitExtraTupleSlot(estate,
                                        RelationGetDescr(rel->localrel),
                                        &TTSOpsVirtual);
 
    /* Process and store remote tuple in the slot */
    oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
    slot_store_data(remoteslot, rel, &newtup);
    slot_fill_defaults(rel, estate, remoteslot);
    MemoryContextSwitchTo(oldctx);
 
    /* For a partitioned table, insert the tuple into a partition. */
    if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
        apply_handle_tuple_routing(edata,
                                   remoteslot, NULL, CMD_INSERT);
    else
    {
        ResultRelInfo *relinfo = edata->targetRelInfo;
 
        ExecOpenIndices(relinfo, false);
        apply_handle_insert_internal(edata, relinfo, remoteslot);
        ExecCloseIndices(relinfo);
    }
 
    finish_edata(edata);
 
    /* Reset relation for error callback */
    apply_error_callback_arg.rel = NULL;
 
    if (!run_as_owner)
        RestoreUserContext(&ucxt);
 
    logicalrep_rel_close(rel, NoLock);
 
    end_replication_step();
}
 
/*
 * Workhorse for apply_handle_insert()
 * relinfo is for the relation we're actually inserting into
 * (could be a child partition of edata->targetRelInfo)
 */
static void
apply_handle_insert_internal(ApplyExecutionData *edata,
                             ResultRelInfo *relinfo,
                             TupleTableSlot *remoteslot)
{
    EState     *estate = edata->estate;
 
    /* Caller should have opened indexes already. */
    Assert(relinfo->ri_IndexRelationDescs != NULL ||
           !relinfo->ri_RelationDesc->rd_rel->relhasindex ||
           RelationGetIndexList(relinfo->ri_RelationDesc) == NIL);
 
    /* Caller will not have done this bit. */
    Assert(relinfo->ri_onConflictArbiterIndexes == NIL);
    InitConflictIndexes(relinfo);
 
    /* Do the insert. */
    TargetPrivilegesCheck(relinfo->ri_RelationDesc, ACL_INSERT);
    ExecSimpleRelationInsert(relinfo, estate, remoteslot);
}
 
/*
 * Check if the logical replication relation is updatable and throw
 * appropriate error if it isn't.
 */
static void
check_relation_updatable(LogicalRepRelMapEntry *rel)
{
    /*
     * For partitioned tables, we only need to care if the target partition is
     * updatable (aka has PK or RI defined for it).
     */
    if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
        return;
 
    /* Updatable, no error. */
    if (rel->updatable)
        return;
 
    /*
     * We are in error mode so it's fine this is somewhat slow. It's better to
     * give user correct error.
     */
    if (OidIsValid(GetRelationIdentityOrPK(rel->localrel)))
    {
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("publisher did not send replica identity column "
                        "expected by the logical replication target relation \"%s.%s\"",
                        rel->remoterel.nspname, rel->remoterel.relname)));
    }
 
    ereport(ERROR,
            (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
             errmsg("logical replication target relation \"%s.%s\" has "
                    "neither REPLICA IDENTITY index nor PRIMARY "
                    "KEY and published relation does not have "
                    "REPLICA IDENTITY FULL",
                    rel->remoterel.nspname, rel->remoterel.relname)));
}
 
/*
 * Handle UPDATE message.
 *
 * TODO: FDW support
 */
static void
apply_handle_update(StringInfo s)
{
    LogicalRepRelMapEntry *rel;
    LogicalRepRelId relid;
    UserContext ucxt;
    ApplyExecutionData *edata;
    EState     *estate;
    LogicalRepTupleData oldtup;
    LogicalRepTupleData newtup;
    bool        has_oldtup;
    TupleTableSlot *remoteslot;
    RTEPermissionInfo *target_perminfo;
    MemoryContext oldctx;
    bool        run_as_owner;
 
    /*
     * Quick return if we are skipping data modification changes or handling
     * streamed transactions.
     */
    if (is_skipping_changes() ||
        handle_streamed_transaction(LOGICAL_REP_MSG_UPDATE, s))
        return;
 
    begin_replication_step();
 
    relid = logicalrep_read_update(s, &has_oldtup, &oldtup,
                                   &newtup);
    rel = logicalrep_rel_open(relid, RowExclusiveLock);
    if (!should_apply_changes_for_rel(rel))
    {
        /*
         * The relation can't become interesting in the middle of the
         * transaction so it's safe to unlock it.
         */
        logicalrep_rel_close(rel, RowExclusiveLock);
        end_replication_step();
        return;
    }
 
    /* Set relation for error callback */
    apply_error_callback_arg.rel = rel;
 
    /* Check if we can do the update. */
    check_relation_updatable(rel);
 
    /*
     * Make sure that any user-supplied code runs as the table owner, unless
     * the user has opted out of that behavior.
     */
    run_as_owner = MySubscription->runasowner;
    if (!run_as_owner)
        SwitchToUntrustedUser(rel->localrel->rd_rel->relowner, &ucxt);
 
    /* Initialize the executor state. */
    edata = create_edata_for_relation(rel);
    estate = edata->estate;
    remoteslot = ExecInitExtraTupleSlot(estate,
                                        RelationGetDescr(rel->localrel),
                                        &TTSOpsVirtual);
 
    /*
     * Populate updatedCols so that per-column triggers can fire, and so
     * executor can correctly pass down indexUnchanged hint.  This could
     * include more columns than were actually changed on the publisher
     * because the logical replication protocol doesn't contain that
     * information.  But it would for example exclude columns that only exist
     * on the subscriber, since we are not touching those.
     */
    target_perminfo = list_nth(estate->es_rteperminfos, 0);
    for (int i = 0; i < remoteslot->tts_tupleDescriptor->natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(remoteslot->tts_tupleDescriptor, i);
        int         remoteattnum = rel->attrmap->attnums[i];
 
        if (!att->attisdropped && remoteattnum >= 0)
        {
            Assert(remoteattnum < newtup.ncols);
            if (newtup.colstatus[remoteattnum] != LOGICALREP_COLUMN_UNCHANGED)
                target_perminfo->updatedCols =
                    bms_add_member(target_perminfo->updatedCols,
                                   i + 1 - FirstLowInvalidHeapAttributeNumber);
        }
    }
 
    /* Build the search tuple. */
    oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
    slot_store_data(remoteslot, rel,
                    has_oldtup ? &oldtup : &newtup);
    MemoryContextSwitchTo(oldctx);
 
    /* For a partitioned table, apply update to correct partition. */
    if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
        apply_handle_tuple_routing(edata,
                                   remoteslot, &newtup, CMD_UPDATE);
    else
        apply_handle_update_internal(edata, edata->targetRelInfo,
                                     remoteslot, &newtup, rel->localindexoid);
 
    finish_edata(edata);
 
    /* Reset relation for error callback */
    apply_error_callback_arg.rel = NULL;
 
    if (!run_as_owner)
        RestoreUserContext(&ucxt);
 
    logicalrep_rel_close(rel, NoLock);
 
    end_replication_step();
}
 
/*
 * Workhorse for apply_handle_update()
 * relinfo is for the relation we're actually updating in
 * (could be a child partition of edata->targetRelInfo)
 */
static void
apply_handle_update_internal(ApplyExecutionData *edata,
                             ResultRelInfo *relinfo,
                             TupleTableSlot *remoteslot,
                             LogicalRepTupleData *newtup,
                             Oid localindexoid)
{
    EState     *estate = edata->estate;
    LogicalRepRelMapEntry *relmapentry = edata->targetRel;
    Relation    localrel = relinfo->ri_RelationDesc;
    EPQState    epqstate;
    TupleTableSlot *localslot = NULL;
    ConflictTupleInfo conflicttuple = {0};
    bool        found;
    MemoryContext oldctx;
 
    EvalPlanQualInit(&epqstate, estate, NULL, NIL, -1, NIL);
    ExecOpenIndices(relinfo, false);
 
    found = FindReplTupleInLocalRel(edata, localrel,
                                    &relmapentry->remoterel,
                                    localindexoid,
                                    remoteslot, &localslot);
 
    /*
     * Tuple found.
     *
     * Note this will fail if there are other conflicting unique indexes.
     */
    if (found)
    {
        /*
         * Report the conflict if the tuple was modified by a different
         * origin.
         */
        if (GetTupleTransactionInfo(localslot, &conflicttuple.xmin,
                                    &conflicttuple.origin, &conflicttuple.ts) &&
            conflicttuple.origin != replorigin_session_origin)
        {
            TupleTableSlot *newslot;
 
            /* Store the new tuple for conflict reporting */
            newslot = table_slot_create(localrel, &estate->es_tupleTable);
            slot_store_data(newslot, relmapentry, newtup);
 
            conflicttuple.slot = localslot;
 
            ReportApplyConflict(estate, relinfo, LOG, CT_UPDATE_ORIGIN_DIFFERS,
                                remoteslot, newslot,
                                list_make1(&conflicttuple));
        }
 
        /* Process and store remote tuple in the slot */
        oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
        slot_modify_data(remoteslot, localslot, relmapentry, newtup);
        MemoryContextSwitchTo(oldctx);
 
        EvalPlanQualSetSlot(&epqstate, remoteslot);
 
        InitConflictIndexes(relinfo);
 
        /* Do the actual update. */
        TargetPrivilegesCheck(relinfo->ri_RelationDesc, ACL_UPDATE);
        ExecSimpleRelationUpdate(relinfo, estate, &epqstate, localslot,
                                 remoteslot);
    }
    else
    {
        ConflictType type;
        TupleTableSlot *newslot = localslot;
 
        /*
         * Detecting whether the tuple was recently deleted or never existed
         * is crucial to avoid misleading the user during conflict handling.
         */
        if (FindDeletedTupleInLocalRel(localrel, localindexoid, remoteslot,
                                       &conflicttuple.xmin,
                                       &conflicttuple.origin,
                                       &conflicttuple.ts) &&
            conflicttuple.origin != replorigin_session_origin)
            type = CT_UPDATE_DELETED;
        else
            type = CT_UPDATE_MISSING;
 
        /* Store the new tuple for conflict reporting */
        slot_store_data(newslot, relmapentry, newtup);
 
        /*
         * The tuple to be updated could not be found or was deleted.  Do
         * nothing except for emitting a log message.
         */
        ReportApplyConflict(estate, relinfo, LOG, type, remoteslot, newslot,
                            list_make1(&conflicttuple));
    }
 
    /* Cleanup. */
    ExecCloseIndices(relinfo);
    EvalPlanQualEnd(&epqstate);
}
 
/*
 * Handle DELETE message.
 *
 * TODO: FDW support
 */
static void
apply_handle_delete(StringInfo s)
{
    LogicalRepRelMapEntry *rel;
    LogicalRepTupleData oldtup;
    LogicalRepRelId relid;
    UserContext ucxt;
    ApplyExecutionData *edata;
    EState     *estate;
    TupleTableSlot *remoteslot;
    MemoryContext oldctx;
    bool        run_as_owner;
 
    /*
     * Quick return if we are skipping data modification changes or handling
     * streamed transactions.
     */
    if (is_skipping_changes() ||
        handle_streamed_transaction(LOGICAL_REP_MSG_DELETE, s))
        return;
 
    begin_replication_step();
 
    relid = logicalrep_read_delete(s, &oldtup);
    rel = logicalrep_rel_open(relid, RowExclusiveLock);
    if (!should_apply_changes_for_rel(rel))
    {
        /*
         * The relation can't become interesting in the middle of the
         * transaction so it's safe to unlock it.
         */
        logicalrep_rel_close(rel, RowExclusiveLock);
        end_replication_step();
        return;
    }
 
    /* Set relation for error callback */
    apply_error_callback_arg.rel = rel;
 
    /* Check if we can do the delete. */
    check_relation_updatable(rel);
 
    /*
     * Make sure that any user-supplied code runs as the table owner, unless
     * the user has opted out of that behavior.
     */
    run_as_owner = MySubscription->runasowner;
    if (!run_as_owner)
        SwitchToUntrustedUser(rel->localrel->rd_rel->relowner, &ucxt);
 
    /* Initialize the executor state. */
    edata = create_edata_for_relation(rel);
    estate = edata->estate;
    remoteslot = ExecInitExtraTupleSlot(estate,
                                        RelationGetDescr(rel->localrel),
                                        &TTSOpsVirtual);
 
    /* Build the search tuple. */
    oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
    slot_store_data(remoteslot, rel, &oldtup);
    MemoryContextSwitchTo(oldctx);
 
    /* For a partitioned table, apply delete to correct partition. */
    if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
        apply_handle_tuple_routing(edata,
                                   remoteslot, NULL, CMD_DELETE);
    else
    {
        ResultRelInfo *relinfo = edata->targetRelInfo;
 
        ExecOpenIndices(relinfo, false);
        apply_handle_delete_internal(edata, relinfo,
                                     remoteslot, rel->localindexoid);
        ExecCloseIndices(relinfo);
    }
 
    finish_edata(edata);
 
    /* Reset relation for error callback */
    apply_error_callback_arg.rel = NULL;
 
    if (!run_as_owner)
        RestoreUserContext(&ucxt);
 
    logicalrep_rel_close(rel, NoLock);
 
    end_replication_step();
}
 
/*
 * Workhorse for apply_handle_delete()
 * relinfo is for the relation we're actually deleting from
 * (could be a child partition of edata->targetRelInfo)
 */
static void
apply_handle_delete_internal(ApplyExecutionData *edata,
                             ResultRelInfo *relinfo,
                             TupleTableSlot *remoteslot,
                             Oid localindexoid)
{
    EState     *estate = edata->estate;
    Relation    localrel = relinfo->ri_RelationDesc;
    LogicalRepRelation *remoterel = &edata->targetRel->remoterel;
    EPQState    epqstate;
    TupleTableSlot *localslot;
    ConflictTupleInfo conflicttuple = {0};
    bool        found;
 
    EvalPlanQualInit(&epqstate, estate, NULL, NIL, -1, NIL);
 
    /* Caller should have opened indexes already. */
    Assert(relinfo->ri_IndexRelationDescs != NULL ||
           !localrel->rd_rel->relhasindex ||
           RelationGetIndexList(localrel) == NIL);
 
    found = FindReplTupleInLocalRel(edata, localrel, remoterel, localindexoid,
                                    remoteslot, &localslot);
 
    /* If found delete it. */
    if (found)
    {
        /*
         * Report the conflict if the tuple was modified by a different
         * origin.
         */
        if (GetTupleTransactionInfo(localslot, &conflicttuple.xmin,
                                    &conflicttuple.origin, &conflicttuple.ts) &&
            conflicttuple.origin != replorigin_session_origin)
        {
            conflicttuple.slot = localslot;
            ReportApplyConflict(estate, relinfo, LOG, CT_DELETE_ORIGIN_DIFFERS,
                                remoteslot, NULL,
                                list_make1(&conflicttuple));
        }
 
        EvalPlanQualSetSlot(&epqstate, localslot);
 
        /* Do the actual delete. */
        TargetPrivilegesCheck(relinfo->ri_RelationDesc, ACL_DELETE);
        ExecSimpleRelationDelete(relinfo, estate, &epqstate, localslot);
    }
    else
    {
        /*
         * The tuple to be deleted could not be found.  Do nothing except for
         * emitting a log message.
         */
        ReportApplyConflict(estate, relinfo, LOG, CT_DELETE_MISSING,
                            remoteslot, NULL, list_make1(&conflicttuple));
    }
 
    /* Cleanup. */
    EvalPlanQualEnd(&epqstate);
}
 
/*
 * Try to find a tuple received from the publication side (in 'remoteslot') in
 * the corresponding local relation using either replica identity index,
 * primary key, index or if needed, sequential scan.
 *
 * Local tuple, if found, is returned in '*localslot'.
 */
static bool
FindReplTupleInLocalRel(ApplyExecutionData *edata, Relation localrel,
                        LogicalRepRelation *remoterel,
                        Oid localidxoid,
                        TupleTableSlot *remoteslot,
                        TupleTableSlot **localslot)
{
    EState     *estate = edata->estate;
    bool        found;
 
    /*
     * Regardless of the top-level operation, we're performing a read here, so
     * check for SELECT privileges.
     */
    TargetPrivilegesCheck(localrel, ACL_SELECT);
 
    *localslot = table_slot_create(localrel, &estate->es_tupleTable);
 
    Assert(OidIsValid(localidxoid) ||
           (remoterel->replident == REPLICA_IDENTITY_FULL));
 
    if (OidIsValid(localidxoid))
    {
#ifdef USE_ASSERT_CHECKING
        Relation    idxrel = index_open(localidxoid, AccessShareLock);
 
        /* Index must be PK, RI, or usable for REPLICA IDENTITY FULL tables */
        Assert(GetRelationIdentityOrPK(localrel) == localidxoid ||
               (remoterel->replident == REPLICA_IDENTITY_FULL &&
                IsIndexUsableForReplicaIdentityFull(idxrel,
                                                    edata->targetRel->attrmap)));
        index_close(idxrel, AccessShareLock);
#endif
 
        found = RelationFindReplTupleByIndex(localrel, localidxoid,
                                             LockTupleExclusive,
                                             remoteslot, *localslot);
    }
    else
        found = RelationFindReplTupleSeq(localrel, LockTupleExclusive,
                                         remoteslot, *localslot);
 
    return found;
}
 
/*
 * Determine whether the index can reliably locate the deleted tuple in the
 * local relation.
 *
 * An index may exclude deleted tuples if it was re-indexed or re-created during
 * change application. Therefore, an index is considered usable only if the
 * conflict detection slot.xmin (conflict_detection_xmin) is greater than the
 * index tuple's xmin. This ensures that any tuples deleted prior to the index
 * creation or re-indexing are not relevant for conflict detection in the
 * current apply worker.
 *
 * Note that indexes may also be excluded if they were modified by other DDL
 * operations, such as ALTER INDEX. However, this is acceptable, as the
 * likelihood of such DDL changes coinciding with the need to scan dead
 * tuples for the update_deleted is low.
 */
static bool
IsIndexUsableForFindingDeletedTuple(Oid localindexoid,
                                    TransactionId conflict_detection_xmin)
{
    HeapTuple   index_tuple;
    TransactionId index_xmin;
 
    index_tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(localindexoid));
 
    if (!HeapTupleIsValid(index_tuple)) /* should not happen */
        elog(ERROR, "cache lookup failed for index %u", localindexoid);
 
    /*
     * No need to check for a frozen transaction ID, as
     * TransactionIdPrecedes() manages it internally, treating it as falling
     * behind the conflict_detection_xmin.
     */
    index_xmin = HeapTupleHeaderGetXmin(index_tuple->t_data);
 
    ReleaseSysCache(index_tuple);
 
    return TransactionIdPrecedes(index_xmin, conflict_detection_xmin);
}
 
/*
 * Attempts to locate a deleted tuple in the local relation that matches the
 * values of the tuple received from the publication side (in 'remoteslot').
 * The search is performed using either the replica identity index, primary
 * key, other available index, or a sequential scan if necessary.
 *
 * Returns true if the deleted tuple is found. If found, the transaction ID,
 * origin, and commit timestamp of the deletion are stored in '*delete_xid',
 * '*delete_origin', and '*delete_time' respectively.
 */
static bool
FindDeletedTupleInLocalRel(Relation localrel, Oid localidxoid,
                           TupleTableSlot *remoteslot,
                           TransactionId *delete_xid, RepOriginId *delete_origin,
                           TimestampTz *delete_time)
{
    TransactionId oldestxmin;
 
    /*
     * Return false if either dead tuples are not retained or commit timestamp
     * data is not available.
     */
    if (!MySubscription->retaindeadtuples || !track_commit_timestamp)
        return false;
 
    /*
     * For conflict detection, we use the leader worker's
     * oldest_nonremovable_xid value instead of invoking
     * GetOldestNonRemovableTransactionId() or using the conflict detection
     * slot's xmin. The oldest_nonremovable_xid acts as a threshold to
     * identify tuples that were recently deleted. These deleted tuples are no
     * longer visible to concurrent transactions. However, if a remote update
     * matches such a tuple, we log an update_deleted conflict.
     *
     * While GetOldestNonRemovableTransactionId() and slot.xmin may return
     * transaction IDs older than oldest_nonremovable_xid, for our current
     * purpose, it is acceptable to treat tuples deleted by transactions prior
     * to oldest_nonremovable_xid as update_missing conflicts.
     */
    if (am_leader_apply_worker())
    {
        oldestxmin = MyLogicalRepWorker->oldest_nonremovable_xid;
    }
    else
    {
        LogicalRepWorker *leader;
 
        /*
         * Obtain the information from the leader apply worker as only the
         * leader manages oldest_nonremovable_xid (see
         * maybe_advance_nonremovable_xid() for details).
         */
        LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
        leader = logicalrep_worker_find(MyLogicalRepWorker->subid,
                                        InvalidOid, false);
        if (!leader)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("could not detect conflict as the leader apply worker has exited")));
        }
 
        SpinLockAcquire(&leader->relmutex);
        oldestxmin = leader->oldest_nonremovable_xid;
        SpinLockRelease(&leader->relmutex);
        LWLockRelease(LogicalRepWorkerLock);
    }
 
    /*
     * Return false if the leader apply worker has stopped retaining
     * information for detecting conflicts. This implies that update_deleted
     * can no longer be reliably detected.
     */
    if (!TransactionIdIsValid(oldestxmin))
        return false;
 
    if (OidIsValid(localidxoid) &&
        IsIndexUsableForFindingDeletedTuple(localidxoid, oldestxmin))
        return RelationFindDeletedTupleInfoByIndex(localrel, localidxoid,
                                                   remoteslot, oldestxmin,
                                                   delete_xid, delete_origin,
                                                   delete_time);
    else
        return RelationFindDeletedTupleInfoSeq(localrel, remoteslot,
                                               oldestxmin, delete_xid,
                                               delete_origin, delete_time);
}
 
/*
 * This handles insert, update, delete on a partitioned table.
 */
static void
apply_handle_tuple_routing(ApplyExecutionData *edata,
                           TupleTableSlot *remoteslot,
                           LogicalRepTupleData *newtup,
                           CmdType operation)
{
    EState     *estate = edata->estate;
    LogicalRepRelMapEntry *relmapentry = edata->targetRel;
    ResultRelInfo *relinfo = edata->targetRelInfo;
    Relation    parentrel = relinfo->ri_RelationDesc;
    ModifyTableState *mtstate;
    PartitionTupleRouting *proute;
    ResultRelInfo *partrelinfo;
    Relation    partrel;
    TupleTableSlot *remoteslot_part;
    TupleConversionMap *map;
    MemoryContext oldctx;
    LogicalRepRelMapEntry *part_entry = NULL;
    AttrMap    *attrmap = NULL;
 
    /* ModifyTableState is needed for ExecFindPartition(). */
    edata->mtstate = mtstate = makeNode(ModifyTableState);
    mtstate->ps.plan = NULL;
    mtstate->ps.state = estate;
    mtstate->operation = operation;
    mtstate->resultRelInfo = relinfo;
 
    /* ... as is PartitionTupleRouting. */
    edata->proute = proute = ExecSetupPartitionTupleRouting(estate, parentrel);
 
    /*
     * Find the partition to which the "search tuple" belongs.
     */
    Assert(remoteslot != NULL);
    oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
    partrelinfo = ExecFindPartition(mtstate, relinfo, proute,
                                    remoteslot, estate);
    Assert(partrelinfo != NULL);
    partrel = partrelinfo->ri_RelationDesc;
 
    /*
     * Check for supported relkind.  We need this since partitions might be of
     * unsupported relkinds; and the set of partitions can change, so checking
     * at CREATE/ALTER SUBSCRIPTION would be insufficient.
     */
    CheckSubscriptionRelkind(partrel->rd_rel->relkind,
                             get_namespace_name(RelationGetNamespace(partrel)),
                             RelationGetRelationName(partrel));
 
    /*
     * To perform any of the operations below, the tuple must match the
     * partition's rowtype. Convert if needed or just copy, using a dedicated
     * slot to store the tuple in any case.
     */
    remoteslot_part = partrelinfo->ri_PartitionTupleSlot;
    if (remoteslot_part == NULL)
        remoteslot_part = table_slot_create(partrel, &estate->es_tupleTable);
    map = ExecGetRootToChildMap(partrelinfo, estate);
    if (map != NULL)
    {
        attrmap = map->attrMap;
        remoteslot_part = execute_attr_map_slot(attrmap, remoteslot,
                                                remoteslot_part);
    }
    else
    {
        remoteslot_part = ExecCopySlot(remoteslot_part, remoteslot);
        slot_getallattrs(remoteslot_part);
    }
    MemoryContextSwitchTo(oldctx);
 
    /* Check if we can do the update or delete on the leaf partition. */
    if (operation == CMD_UPDATE || operation == CMD_DELETE)
    {
        part_entry = logicalrep_partition_open(relmapentry, partrel,
                                               attrmap);
        check_relation_updatable(part_entry);
    }
 
    switch (operation)
    {
        case CMD_INSERT:
            apply_handle_insert_internal(edata, partrelinfo,
                                         remoteslot_part);
            break;
 
        case CMD_DELETE:
            apply_handle_delete_internal(edata, partrelinfo,
                                         remoteslot_part,
                                         part_entry->localindexoid);
            break;
 
        case CMD_UPDATE:
 
            /*
             * For UPDATE, depending on whether or not the updated tuple
             * satisfies the partition's constraint, perform a simple UPDATE
             * of the partition or move the updated tuple into a different
             * suitable partition.
             */
            {
                TupleTableSlot *localslot;
                ResultRelInfo *partrelinfo_new;
                Relation    partrel_new;
                bool        found;
                EPQState    epqstate;
                ConflictTupleInfo conflicttuple = {0};
 
                /* Get the matching local tuple from the partition. */
                found = FindReplTupleInLocalRel(edata, partrel,
                                                &part_entry->remoterel,
                                                part_entry->localindexoid,
                                                remoteslot_part, &localslot);
                if (!found)
                {
                    ConflictType type;
                    TupleTableSlot *newslot = localslot;
 
                    /*
                     * Detecting whether the tuple was recently deleted or
                     * never existed is crucial to avoid misleading the user
                     * during conflict handling.
                     */
                    if (FindDeletedTupleInLocalRel(partrel,
                                                   part_entry->localindexoid,
                                                   remoteslot_part,
                                                   &conflicttuple.xmin,
                                                   &conflicttuple.origin,
                                                   &conflicttuple.ts) &&
                        conflicttuple.origin != replorigin_session_origin)
                        type = CT_UPDATE_DELETED;
                    else
                        type = CT_UPDATE_MISSING;
 
                    /* Store the new tuple for conflict reporting */
                    slot_store_data(newslot, part_entry, newtup);
 
                    /*
                     * The tuple to be updated could not be found or was
                     * deleted.  Do nothing except for emitting a log message.
                     */
                    ReportApplyConflict(estate, partrelinfo, LOG,
                                        type, remoteslot_part, newslot,
                                        list_make1(&conflicttuple));
 
                    return;
                }
 
                /*
                 * Report the conflict if the tuple was modified by a
                 * different origin.
                 */
                if (GetTupleTransactionInfo(localslot, &conflicttuple.xmin,
                                            &conflicttuple.origin,
                                            &conflicttuple.ts) &&
                    conflicttuple.origin != replorigin_session_origin)
                {
                    TupleTableSlot *newslot;
 
                    /* Store the new tuple for conflict reporting */
                    newslot = table_slot_create(partrel, &estate->es_tupleTable);
                    slot_store_data(newslot, part_entry, newtup);
 
                    conflicttuple.slot = localslot;
 
                    ReportApplyConflict(estate, partrelinfo, LOG, CT_UPDATE_ORIGIN_DIFFERS,
                                        remoteslot_part, newslot,
                                        list_make1(&conflicttuple));
                }
 
                /*
                 * Apply the update to the local tuple, putting the result in
                 * remoteslot_part.
                 */
                oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
                slot_modify_data(remoteslot_part, localslot, part_entry,
                                 newtup);
                MemoryContextSwitchTo(oldctx);
 
                EvalPlanQualInit(&epqstate, estate, NULL, NIL, -1, NIL);
 
                /*
                 * Does the updated tuple still satisfy the current
                 * partition's constraint?
                 */
                if (!partrel->rd_rel->relispartition ||
                    ExecPartitionCheck(partrelinfo, remoteslot_part, estate,
                                       false))
                {
                    /*
                     * Yes, so simply UPDATE the partition.  We don't call
                     * apply_handle_update_internal() here, which would
                     * normally do the following work, to avoid repeating some
                     * work already done above to find the local tuple in the
                     * partition.
                     */
                    InitConflictIndexes(partrelinfo);
 
                    EvalPlanQualSetSlot(&epqstate, remoteslot_part);
                    TargetPrivilegesCheck(partrelinfo->ri_RelationDesc,
                                          ACL_UPDATE);
                    ExecSimpleRelationUpdate(partrelinfo, estate, &epqstate,
                                             localslot, remoteslot_part);
                }
                else
                {
                    /* Move the tuple into the new partition. */
 
                    /*
                     * New partition will be found using tuple routing, which
                     * can only occur via the parent table.  We might need to
                     * convert the tuple to the parent's rowtype.  Note that
                     * this is the tuple found in the partition, not the
                     * original search tuple received by this function.
                     */
                    if (map)
                    {
                        TupleConversionMap *PartitionToRootMap =
                            convert_tuples_by_name(RelationGetDescr(partrel),
                                                   RelationGetDescr(parentrel));
 
                        remoteslot =
                            execute_attr_map_slot(PartitionToRootMap->attrMap,
                                                  remoteslot_part, remoteslot);
                    }
                    else
                    {
                        remoteslot = ExecCopySlot(remoteslot, remoteslot_part);
                        slot_getallattrs(remoteslot);
                    }
 
                    /* Find the new partition. */
                    oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
                    partrelinfo_new = ExecFindPartition(mtstate, relinfo,
                                                        proute, remoteslot,
                                                        estate);
                    MemoryContextSwitchTo(oldctx);
                    Assert(partrelinfo_new != partrelinfo);
                    partrel_new = partrelinfo_new->ri_RelationDesc;
 
                    /* Check that new partition also has supported relkind. */
                    CheckSubscriptionRelkind(partrel_new->rd_rel->relkind,
                                             get_namespace_name(RelationGetNamespace(partrel_new)),
                                             RelationGetRelationName(partrel_new));
 
                    /* DELETE old tuple found in the old partition. */
                    EvalPlanQualSetSlot(&epqstate, localslot);
                    TargetPrivilegesCheck(partrelinfo->ri_RelationDesc, ACL_DELETE);
                    ExecSimpleRelationDelete(partrelinfo, estate, &epqstate, localslot);
 
                    /* INSERT new tuple into the new partition. */
 
                    /*
                     * Convert the replacement tuple to match the destination
                     * partition rowtype.
                     */
                    oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
                    remoteslot_part = partrelinfo_new->ri_PartitionTupleSlot;
                    if (remoteslot_part == NULL)
                        remoteslot_part = table_slot_create(partrel_new,
                                                            &estate->es_tupleTable);
                    map = ExecGetRootToChildMap(partrelinfo_new, estate);
                    if (map != NULL)
                    {
                        remoteslot_part = execute_attr_map_slot(map->attrMap,
                                                                remoteslot,
                                                                remoteslot_part);
                    }
                    else
                    {
                        remoteslot_part = ExecCopySlot(remoteslot_part,
                                                       remoteslot);
                        slot_getallattrs(remoteslot);
                    }
                    MemoryContextSwitchTo(oldctx);
                    apply_handle_insert_internal(edata, partrelinfo_new,
                                                 remoteslot_part);
                }
 
                EvalPlanQualEnd(&epqstate);
            }
            break;
 
        default:
            elog(ERROR, "unrecognized CmdType: %d", (int) operation);
            break;
    }
}
 
/*
 * Handle TRUNCATE message.
 *
 * TODO: FDW support
 */
static void
apply_handle_truncate(StringInfo s)
{
    bool        cascade = false;
    bool        restart_seqs = false;
    List       *remote_relids = NIL;
    List       *remote_rels = NIL;
    List       *rels = NIL;
    List       *part_rels = NIL;
    List       *relids = NIL;
    List       *relids_logged = NIL;
    ListCell   *lc;
    LOCKMODE    lockmode = AccessExclusiveLock;
 
    /*
     * Quick return if we are skipping data modification changes or handling
     * streamed transactions.
     */
    if (is_skipping_changes() ||
        handle_streamed_transaction(LOGICAL_REP_MSG_TRUNCATE, s))
        return;
 
    begin_replication_step();
 
    remote_relids = logicalrep_read_truncate(s, &cascade, &restart_seqs);
 
    foreach(lc, remote_relids)
    {
        LogicalRepRelId relid = lfirst_oid(lc);
        LogicalRepRelMapEntry *rel;
 
        rel = logicalrep_rel_open(relid, lockmode);
        if (!should_apply_changes_for_rel(rel))
        {
            /*
             * The relation can't become interesting in the middle of the
             * transaction so it's safe to unlock it.
             */
            logicalrep_rel_close(rel, lockmode);
            continue;
        }
 
        remote_rels = lappend(remote_rels, rel);
        TargetPrivilegesCheck(rel->localrel, ACL_TRUNCATE);
        rels = lappend(rels, rel->localrel);
        relids = lappend_oid(relids, rel->localreloid);
        if (RelationIsLogicallyLogged(rel->localrel))
            relids_logged = lappend_oid(relids_logged, rel->localreloid);
 
        /*
         * Truncate partitions if we got a message to truncate a partitioned
         * table.
         */
        if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
        {
            ListCell   *child;
            List       *children = find_all_inheritors(rel->localreloid,
                                                       lockmode,
                                                       NULL);
 
            foreach(child, children)
            {
                Oid         childrelid = lfirst_oid(child);
                Relation    childrel;
 
                if (list_member_oid(relids, childrelid))
                    continue;
 
                /* find_all_inheritors already got lock */
                childrel = table_open(childrelid, NoLock);
 
                /*
                 * Ignore temp tables of other backends.  See similar code in
                 * ExecuteTruncate().
                 */
                if (RELATION_IS_OTHER_TEMP(childrel))
                {
                    table_close(childrel, lockmode);
                    continue;
                }
 
                TargetPrivilegesCheck(childrel, ACL_TRUNCATE);
                rels = lappend(rels, childrel);
                part_rels = lappend(part_rels, childrel);
                relids = lappend_oid(relids, childrelid);
                /* Log this relation only if needed for logical decoding */
                if (RelationIsLogicallyLogged(childrel))
                    relids_logged = lappend_oid(relids_logged, childrelid);
            }
        }
    }
 
    /*
     * Even if we used CASCADE on the upstream primary we explicitly default
     * to replaying changes without further cascading. This might be later
     * changeable with a user specified option.
     *
     * MySubscription->runasowner tells us whether we want to execute
     * replication actions as the subscription owner; the last argument to
     * TruncateGuts tells it whether we want to switch to the table owner.
     * Those are exactly opposite conditions.
     */
    ExecuteTruncateGuts(rels,
                        relids,
                        relids_logged,
                        DROP_RESTRICT,
                        restart_seqs,
                        !MySubscription->runasowner);
    foreach(lc, remote_rels)
    {
        LogicalRepRelMapEntry *rel = lfirst(lc);
 
        logicalrep_rel_close(rel, NoLock);
    }
    foreach(lc, part_rels)
    {
        Relation    rel = lfirst(lc);
 
        table_close(rel, NoLock);
    }
 
    end_replication_step();
}
 
 
/*
 * Logical replication protocol message dispatcher.
 */
void
apply_dispatch(StringInfo s)
{
    LogicalRepMsgType action = pq_getmsgbyte(s);
    LogicalRepMsgType saved_command;
 
    /*
     * Set the current command being applied. Since this function can be
     * called recursively when applying spooled changes, save the current
     * command.
     */
    saved_command = apply_error_callback_arg.command;
    apply_error_callback_arg.command = action;
 
    switch (action)
    {
        case LOGICAL_REP_MSG_BEGIN:
            apply_handle_begin(s);
            break;
 
        case LOGICAL_REP_MSG_COMMIT:
            apply_handle_commit(s);
            break;
 
        case LOGICAL_REP_MSG_INSERT:
            apply_handle_insert(s);
            break;
 
        case LOGICAL_REP_MSG_UPDATE:
            apply_handle_update(s);
            break;
 
        case LOGICAL_REP_MSG_DELETE:
            apply_handle_delete(s);
            break;
 
        case LOGICAL_REP_MSG_TRUNCATE:
            apply_handle_truncate(s);
            break;
 
        case LOGICAL_REP_MSG_RELATION:
            apply_handle_relation(s);
            break;
 
        case LOGICAL_REP_MSG_TYPE:
            apply_handle_type(s);
            break;
 
        case LOGICAL_REP_MSG_ORIGIN:
            apply_handle_origin(s);
            break;
 
        case LOGICAL_REP_MSG_MESSAGE:
 
            /*
             * Logical replication does not use generic logical messages yet.
             * Although, it could be used by other applications that use this
             * output plugin.
             */
            break;
 
        case LOGICAL_REP_MSG_STREAM_START:
            apply_handle_stream_start(s);
            break;
 
        case LOGICAL_REP_MSG_STREAM_STOP:
            apply_handle_stream_stop(s);
            break;
 
        case LOGICAL_REP_MSG_STREAM_ABORT:
            apply_handle_stream_abort(s);
            break;
 
        case LOGICAL_REP_MSG_STREAM_COMMIT:
            apply_handle_stream_commit(s);
            break;
 
        case LOGICAL_REP_MSG_BEGIN_PREPARE:
            apply_handle_begin_prepare(s);
            break;
 
        case LOGICAL_REP_MSG_PREPARE:
            apply_handle_prepare(s);
            break;
 
        case LOGICAL_REP_MSG_COMMIT_PREPARED:
            apply_handle_commit_prepared(s);
            break;
 
        case LOGICAL_REP_MSG_ROLLBACK_PREPARED:
            apply_handle_rollback_prepared(s);
            break;
 
        case LOGICAL_REP_MSG_STREAM_PREPARE:
            apply_handle_stream_prepare(s);
            break;
 
        default:
            ereport(ERROR,
                    (errcode(ERRCODE_PROTOCOL_VIOLATION),
                     errmsg("invalid logical replication message type \"??? (%d)\"", action)));
    }
 
    /* Reset the current command */
    apply_error_callback_arg.command = saved_command;
}
 
/*
 * Figure out which write/flush positions to report to the walsender process.
 *
 * We can't simply report back the last LSN the walsender sent us because the
 * local transaction might not yet be flushed to disk locally. Instead we
 * build a list that associates local with remote LSNs for every commit. When
 * reporting back the flush position to the sender we iterate that list and
 * check which entries on it are already locally flushed. Those we can report
 * as having been flushed.
 *
 * The have_pending_txes is true if there are outstanding transactions that
 * need to be flushed.
 */
static void
get_flush_position(XLogRecPtr *write, XLogRecPtr *flush,
                   bool *have_pending_txes)
{
    dlist_mutable_iter iter;
    XLogRecPtr  local_flush = GetFlushRecPtr(NULL);
 
    *write = InvalidXLogRecPtr;
    *flush = InvalidXLogRecPtr;
 
    dlist_foreach_modify(iter, &lsn_mapping)
    {
        FlushPosition *pos =
            dlist_container(FlushPosition, node, iter.cur);
 
        *write = pos->remote_end;
 
        if (pos->local_end <= local_flush)
        {
            *flush = pos->remote_end;
            dlist_delete(iter.cur);
            pfree(pos);
        }
        else
        {
            /*
             * Don't want to uselessly iterate over the rest of the list which
             * could potentially be long. Instead get the last element and
             * grab the write position from there.
             */
            pos = dlist_tail_element(FlushPosition, node,
                                     &lsn_mapping);
            *write = pos->remote_end;
            *have_pending_txes = true;
            return;
        }
    }
 
    *have_pending_txes = !dlist_is_empty(&lsn_mapping);
}
 
/*
 * Store current remote/local lsn pair in the tracking list.
 */
void
store_flush_position(XLogRecPtr remote_lsn, XLogRecPtr local_lsn)
{
    FlushPosition *flushpos;
 
    /*
     * Skip for parallel apply workers, because the lsn_mapping is maintained
     * by the leader apply worker.
     */
    if (am_parallel_apply_worker())
        return;
 
    /* Need to do this in permanent context */
    MemoryContextSwitchTo(ApplyContext);
 
    /* Track commit lsn  */
    flushpos = (FlushPosition *) palloc(sizeof(FlushPosition));
    flushpos->local_end = local_lsn;
    flushpos->remote_end = remote_lsn;
 
    dlist_push_tail(&lsn_mapping, &flushpos->node);
    MemoryContextSwitchTo(ApplyMessageContext);
}
 
 
/* Update statistics of the worker. */
static void
UpdateWorkerStats(XLogRecPtr last_lsn, TimestampTz send_time, bool reply)
{
    MyLogicalRepWorker->last_lsn = last_lsn;
    MyLogicalRepWorker->last_send_time = send_time;
    MyLogicalRepWorker->last_recv_time = GetCurrentTimestamp();
    if (reply)
    {
        MyLogicalRepWorker->reply_lsn = last_lsn;
        MyLogicalRepWorker->reply_time = send_time;
    }
}
 
/*
 * Apply main loop.
 */
static void
LogicalRepApplyLoop(XLogRecPtr last_received)
{
    TimestampTz last_recv_timestamp = GetCurrentTimestamp();
    bool        ping_sent = false;
    TimeLineID  tli;
    ErrorContextCallback errcallback;
    RetainDeadTuplesData rdt_data = {0};
 
    /*
     * Init the ApplyMessageContext which we clean up after each replication
     * protocol message.
     */
    ApplyMessageContext = AllocSetContextCreate(ApplyContext,
                                                "ApplyMessageContext",
                                                ALLOCSET_DEFAULT_SIZES);
 
    /*
     * This memory context is used for per-stream data when the streaming mode
     * is enabled. This context is reset on each stream stop.
     */
    LogicalStreamingContext = AllocSetContextCreate(ApplyContext,
                                                    "LogicalStreamingContext",
                                                    ALLOCSET_DEFAULT_SIZES);
 
    /* mark as idle, before starting to loop */
    pgstat_report_activity(STATE_IDLE, NULL);
 
    /*
     * Push apply error context callback. Fields will be filled while applying
     * a change.
     */
    errcallback.callback = apply_error_callback;
    errcallback.previous = error_context_stack;
    error_context_stack = &errcallback;
    apply_error_context_stack = error_context_stack;
 
    /* This outer loop iterates once per wait. */
    for (;;)
    {
        pgsocket    fd = PGINVALID_SOCKET;
        int         rc;
        int         len;
        char       *buf = NULL;
        bool        endofstream = false;
        long        wait_time;
 
        CHECK_FOR_INTERRUPTS();
 
        MemoryContextSwitchTo(ApplyMessageContext);
 
        len = walrcv_receive(LogRepWorkerWalRcvConn, &buf, &fd);
 
        if (len != 0)
        {
            /* Loop to process all available data (without blocking). */
            for (;;)
            {
                CHECK_FOR_INTERRUPTS();
 
                if (len == 0)
                {
                    break;
                }
                else if (len < 0)
                {
                    ereport(LOG,
                            (errmsg("data stream from publisher has ended")));
                    endofstream = true;
                    break;
                }
                else
                {
                    int         c;
                    StringInfoData s;
 
                    if (ConfigReloadPending)
                    {
                        ConfigReloadPending = false;
                        ProcessConfigFile(PGC_SIGHUP);
                    }
 
                    /* Reset timeout. */
                    last_recv_timestamp = GetCurrentTimestamp();
                    ping_sent = false;
 
                    rdt_data.last_recv_time = last_recv_timestamp;
 
                    /* Ensure we are reading the data into our memory context. */
                    MemoryContextSwitchTo(ApplyMessageContext);
 
                    initReadOnlyStringInfo(&s, buf, len);
 
                    c = pq_getmsgbyte(&s);
 
                    if (c == PqReplMsg_WALData)
                    {
                        XLogRecPtr  start_lsn;
                        XLogRecPtr  end_lsn;
                        TimestampTz send_time;
 
                        start_lsn = pq_getmsgint64(&s);
                        end_lsn = pq_getmsgint64(&s);
                        send_time = pq_getmsgint64(&s);
 
                        if (last_received < start_lsn)
                            last_received = start_lsn;
 
                        if (last_received < end_lsn)
                            last_received = end_lsn;
 
                        UpdateWorkerStats(last_received, send_time, false);
 
                        apply_dispatch(&s);
 
                        maybe_advance_nonremovable_xid(&rdt_data, false);
                    }
                    else if (c == PqReplMsg_Keepalive)
                    {
                        XLogRecPtr  end_lsn;
                        TimestampTz timestamp;
                        bool        reply_requested;
 
                        end_lsn = pq_getmsgint64(&s);
                        timestamp = pq_getmsgint64(&s);
                        reply_requested = pq_getmsgbyte(&s);
 
                        if (last_received < end_lsn)
                            last_received = end_lsn;
 
                        send_feedback(last_received, reply_requested, false);
 
                        maybe_advance_nonremovable_xid(&rdt_data, false);
 
                        UpdateWorkerStats(last_received, timestamp, true);
                    }
                    else if (c == PqReplMsg_PrimaryStatusUpdate)
                    {
                        rdt_data.remote_lsn = pq_getmsgint64(&s);
                        rdt_data.remote_oldestxid = FullTransactionIdFromU64((uint64) pq_getmsgint64(&s));
                        rdt_data.remote_nextxid = FullTransactionIdFromU64((uint64) pq_getmsgint64(&s));
                        rdt_data.reply_time = pq_getmsgint64(&s);
 
                        /*
                         * This should never happen, see
                         * ProcessStandbyPSRequestMessage. But if it happens
                         * due to a bug, we don't want to proceed as it can
                         * incorrectly advance oldest_nonremovable_xid.
                         */
                        if (XLogRecPtrIsInvalid(rdt_data.remote_lsn))
                            elog(ERROR, "cannot get the latest WAL position from the publisher");
 
                        maybe_advance_nonremovable_xid(&rdt_data, true);
 
                        UpdateWorkerStats(last_received, rdt_data.reply_time, false);
                    }
                    /* other message types are purposefully ignored */
 
                    MemoryContextReset(ApplyMessageContext);
                }
 
                len = walrcv_receive(LogRepWorkerWalRcvConn, &buf, &fd);
            }
        }
 
        /* confirm all writes so far */
        send_feedback(last_received, false, false);
 
        /* Reset the timestamp if no message was received */
        rdt_data.last_recv_time = 0;
 
        maybe_advance_nonremovable_xid(&rdt_data, false);
 
        if (!in_remote_transaction && !in_streamed_transaction)
        {
            /*
             * If we didn't get any transactions for a while there might be
             * unconsumed invalidation messages in the queue, consume them
             * now.
             */
            AcceptInvalidationMessages();
            maybe_reread_subscription();
 
            /* Process any table synchronization changes. */
            process_syncing_tables(last_received);
        }
 
        /* Cleanup the memory. */
        MemoryContextReset(ApplyMessageContext);
        MemoryContextSwitchTo(TopMemoryContext);
 
        /* Check if we need to exit the streaming loop. */
        if (endofstream)
            break;
 
        /*
         * Wait for more data or latch.  If we have unflushed transactions,
         * wake up after WalWriterDelay to see if they've been flushed yet (in
         * which case we should send a feedback message).  Otherwise, there's
         * no particular urgency about waking up unless we get data or a
         * signal.
         */
        if (!dlist_is_empty(&lsn_mapping))
            wait_time = WalWriterDelay;
        else
            wait_time = NAPTIME_PER_CYCLE;
 
        /*
         * Ensure to wake up when it's possible to advance the non-removable
         * transaction ID, or when the retention duration may have exceeded
         * max_retention_duration.
         */
        if (MySubscription->retentionactive)
        {
            if (rdt_data.phase == RDT_GET_CANDIDATE_XID &&
                rdt_data.xid_advance_interval)
                wait_time = Min(wait_time, rdt_data.xid_advance_interval);
            else if (MySubscription->maxretention > 0)
                wait_time = Min(wait_time, MySubscription->maxretention);
        }
 
        rc = WaitLatchOrSocket(MyLatch,
                               WL_SOCKET_READABLE | WL_LATCH_SET |
                               WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
                               fd, wait_time,
                               WAIT_EVENT_LOGICAL_APPLY_MAIN);
 
        if (rc & WL_LATCH_SET)
        {
            ResetLatch(MyLatch);
            CHECK_FOR_INTERRUPTS();
        }
 
        if (ConfigReloadPending)
        {
            ConfigReloadPending = false;
            ProcessConfigFile(PGC_SIGHUP);
        }
 
        if (rc & WL_TIMEOUT)
        {
            /*
             * We didn't receive anything new. If we haven't heard anything
             * from the server for more than wal_receiver_timeout / 2, ping
             * the server. Also, if it's been longer than
             * wal_receiver_status_interval since the last update we sent,
             * send a status update to the primary anyway, to report any
             * progress in applying WAL.
             */
            bool        requestReply = false;
 
            /*
             * Check if time since last receive from primary has reached the
             * configured limit.
             */
            if (wal_receiver_timeout > 0)
            {
                TimestampTz now = GetCurrentTimestamp();
                TimestampTz timeout;
 
                timeout =
                    TimestampTzPlusMilliseconds(last_recv_timestamp,
                                                wal_receiver_timeout);
 
                if (now >= timeout)
                    ereport(ERROR,
                            (errcode(ERRCODE_CONNECTION_FAILURE),
                             errmsg("terminating logical replication worker due to timeout")));
 
                /* Check to see if it's time for a ping. */
                if (!ping_sent)
                {
                    timeout = TimestampTzPlusMilliseconds(last_recv_timestamp,
                                                          (wal_receiver_timeout / 2));
                    if (now >= timeout)
                    {
                        requestReply = true;
                        ping_sent = true;
                    }
                }
            }
 
            send_feedback(last_received, requestReply, requestReply);
 
            maybe_advance_nonremovable_xid(&rdt_data, false);
 
            /*
             * Force reporting to ensure long idle periods don't lead to
             * arbitrarily delayed stats. Stats can only be reported outside
             * of (implicit or explicit) transactions. That shouldn't lead to
             * stats being delayed for long, because transactions are either
             * sent as a whole on commit or streamed. Streamed transactions
             * are spilled to disk and applied on commit.
             */
            if (!IsTransactionState())
                pgstat_report_stat(true);
        }
    }
 
    /* Pop the error context stack */
    error_context_stack = errcallback.previous;
    apply_error_context_stack = error_context_stack;
 
    /* All done */
    walrcv_endstreaming(LogRepWorkerWalRcvConn, &tli);
}
 
/*
 * Send a Standby Status Update message to server.
 *
 * 'recvpos' is the latest LSN we've received data to, force is set if we need
 * to send a response to avoid timeouts.
 */
static void
send_feedback(XLogRecPtr recvpos, bool force, bool requestReply)
{
    static StringInfo reply_message = NULL;
    static TimestampTz send_time = 0;
 
    static XLogRecPtr last_recvpos = InvalidXLogRecPtr;
    static XLogRecPtr last_writepos = InvalidXLogRecPtr;
 
    XLogRecPtr  writepos;
    XLogRecPtr  flushpos;
    TimestampTz now;
    bool        have_pending_txes;
 
    /*
     * If the user doesn't want status to be reported to the publisher, be
     * sure to exit before doing anything at all.
     */
    if (!force && wal_receiver_status_interval <= 0)
        return;
 
    /* It's legal to not pass a recvpos */
    if (recvpos < last_recvpos)
        recvpos = last_recvpos;
 
    get_flush_position(&writepos, &flushpos, &have_pending_txes);
 
    /*
     * No outstanding transactions to flush, we can report the latest received
     * position. This is important for synchronous replication.
     */
    if (!have_pending_txes)
        flushpos = writepos = recvpos;
 
    if (writepos < last_writepos)
        writepos = last_writepos;
 
    if (flushpos < last_flushpos)
        flushpos = last_flushpos;
 
    now = GetCurrentTimestamp();
 
    /* if we've already reported everything we're good */
    if (!force &&
        writepos == last_writepos &&
        flushpos == last_flushpos &&
        !TimestampDifferenceExceeds(send_time, now,
                                    wal_receiver_status_interval * 1000))
        return;
    send_time = now;
 
    if (!reply_message)
    {
        MemoryContext oldctx = MemoryContextSwitchTo(ApplyContext);
 
        reply_message = makeStringInfo();
        MemoryContextSwitchTo(oldctx);
    }
    else
        resetStringInfo(reply_message);
 
    pq_sendbyte(reply_message, PqReplMsg_StandbyStatusUpdate);
    pq_sendint64(reply_message, recvpos);   /* write */
    pq_sendint64(reply_message, flushpos);  /* flush */
    pq_sendint64(reply_message, writepos);  /* apply */
    pq_sendint64(reply_message, now);   /* sendTime */
    pq_sendbyte(reply_message, requestReply);   /* replyRequested */
 
    elog(DEBUG2, "sending feedback (force %d) to recv %X/%08X, write %X/%08X, flush %X/%08X",
         force,
         LSN_FORMAT_ARGS(recvpos),
         LSN_FORMAT_ARGS(writepos),
         LSN_FORMAT_ARGS(flushpos));
 
    walrcv_send(LogRepWorkerWalRcvConn,
                reply_message->data, reply_message->len);
 
    if (recvpos > last_recvpos)
        last_recvpos = recvpos;
    if (writepos > last_writepos)
        last_writepos = writepos;
    if (flushpos > last_flushpos)
        last_flushpos = flushpos;
}
 
/*
 * Attempt to advance the non-removable transaction ID.
 *
 * See comments atop worker.c for details.
 */
static void
maybe_advance_nonremovable_xid(RetainDeadTuplesData *rdt_data,
                               bool status_received)
{
    if (!can_advance_nonremovable_xid(rdt_data))
        return;
 
    process_rdt_phase_transition(rdt_data, status_received);
}
 
/*
 * Preliminary check to determine if advancing the non-removable transaction ID
 * is allowed.
 */
static bool
can_advance_nonremovable_xid(RetainDeadTuplesData *rdt_data)
{
    /*
     * It is sufficient to manage non-removable transaction ID for a
     * subscription by the main apply worker to detect update_deleted reliably
     * even for table sync or parallel apply workers.
     */
    if (!am_leader_apply_worker())
        return false;
 
    /* No need to advance if retaining dead tuples is not required */
    if (!MySubscription->retaindeadtuples)
        return false;
 
    return true;
}
 
/*
 * Process phase transitions during the non-removable transaction ID
 * advancement. See comments atop worker.c for details of the transition.
 */
static void
process_rdt_phase_transition(RetainDeadTuplesData *rdt_data,
                             bool status_received)
{
    switch (rdt_data->phase)
    {
        case RDT_GET_CANDIDATE_XID:
            get_candidate_xid(rdt_data);
            break;
        case RDT_REQUEST_PUBLISHER_STATUS:
            request_publisher_status(rdt_data);
            break;
        case RDT_WAIT_FOR_PUBLISHER_STATUS:
            wait_for_publisher_status(rdt_data, status_received);
            break;
        case RDT_WAIT_FOR_LOCAL_FLUSH:
            wait_for_local_flush(rdt_data);
            break;
        case RDT_STOP_CONFLICT_INFO_RETENTION:
            stop_conflict_info_retention(rdt_data);
            break;
        case RDT_RESUME_CONFLICT_INFO_RETENTION:
            resume_conflict_info_retention(rdt_data);
            break;
    }
}
 
/*
 * Workhorse for the RDT_GET_CANDIDATE_XID phase.
 */
static void
get_candidate_xid(RetainDeadTuplesData *rdt_data)
{
    TransactionId oldest_running_xid;
    TimestampTz now;
 
    /*
     * Use last_recv_time when applying changes in the loop to avoid
     * unnecessary system time retrieval. If last_recv_time is not available,
     * obtain the current timestamp.
     */
    now = rdt_data->last_recv_time ? rdt_data->last_recv_time : GetCurrentTimestamp();
 
    /*
     * Compute the candidate_xid and request the publisher status at most once
     * per xid_advance_interval. Refer to adjust_xid_advance_interval() for
     * details on how this value is dynamically adjusted. This is to avoid
     * using CPU and network resources without making much progress.
     */
    if (!TimestampDifferenceExceeds(rdt_data->candidate_xid_time, now,
                                    rdt_data->xid_advance_interval))
        return;
 
    /*
     * Immediately update the timer, even if the function returns later
     * without setting candidate_xid due to inactivity on the subscriber. This
     * avoids frequent calls to GetOldestActiveTransactionId.
     */
    rdt_data->candidate_xid_time = now;
 
    /*
     * Consider transactions in the current database, as only dead tuples from
     * this database are required for conflict detection.
     */
    oldest_running_xid = GetOldestActiveTransactionId(false, false);
 
    /*
     * Oldest active transaction ID (oldest_running_xid) can't be behind any
     * of its previously computed value.
     */
    Assert(TransactionIdPrecedesOrEquals(MyLogicalRepWorker->oldest_nonremovable_xid,
                                         oldest_running_xid));
 
    /* Return if the oldest_nonremovable_xid cannot be advanced */
    if (TransactionIdEquals(MyLogicalRepWorker->oldest_nonremovable_xid,
                            oldest_running_xid))
    {
        adjust_xid_advance_interval(rdt_data, false);
        return;
    }
 
    adjust_xid_advance_interval(rdt_data, true);
 
    rdt_data->candidate_xid = oldest_running_xid;
    rdt_data->phase = RDT_REQUEST_PUBLISHER_STATUS;
 
    /* process the next phase */
    process_rdt_phase_transition(rdt_data, false);
}
 
/*
 * Workhorse for the RDT_REQUEST_PUBLISHER_STATUS phase.
 */
static void
request_publisher_status(RetainDeadTuplesData *rdt_data)
{
    static StringInfo request_message = NULL;
 
    if (!request_message)
    {
        MemoryContext oldctx = MemoryContextSwitchTo(ApplyContext);
 
        request_message = makeStringInfo();
        MemoryContextSwitchTo(oldctx);
    }
    else
        resetStringInfo(request_message);
 
    /*
     * Send the current time to update the remote walsender's latest reply
     * message received time.
     */
    pq_sendbyte(request_message, PqReplMsg_PrimaryStatusRequest);
    pq_sendint64(request_message, GetCurrentTimestamp());
 
    elog(DEBUG2, "sending publisher status request message");
 
    /* Send a request for the publisher status */
    walrcv_send(LogRepWorkerWalRcvConn,
                request_message->data, request_message->len);
 
    rdt_data->phase = RDT_WAIT_FOR_PUBLISHER_STATUS;
 
    /*
     * Skip calling maybe_advance_nonremovable_xid() since further transition
     * is possible only once we receive the publisher status message.
     */
}
 
/*
 * Workhorse for the RDT_WAIT_FOR_PUBLISHER_STATUS phase.
 */
static void
wait_for_publisher_status(RetainDeadTuplesData *rdt_data,
                          bool status_received)
{
    /*
     * Return if we have requested but not yet received the publisher status.
     */
    if (!status_received)
        return;
 
    /*
     * We don't need to maintain oldest_nonremovable_xid if we decide to stop
     * retaining conflict information for this worker.
     */
    if (should_stop_conflict_info_retention(rdt_data))
    {
        rdt_data->phase = RDT_STOP_CONFLICT_INFO_RETENTION;
        return;
    }
 
    if (!FullTransactionIdIsValid(rdt_data->remote_wait_for))
        rdt_data->remote_wait_for = rdt_data->remote_nextxid;
 
    /*
     * Check if all remote concurrent transactions that were active at the
     * first status request have now completed. If completed, proceed to the
     * next phase; otherwise, continue checking the publisher status until
     * these transactions finish.
     *
     * It's possible that transactions in the commit phase during the last
     * cycle have now finished committing, but remote_oldestxid remains older
     * than remote_wait_for. This can happen if some old transaction came in
     * the commit phase when we requested status in this cycle. We do not
     * handle this case explicitly as it's rare and the benefit doesn't
     * justify the required complexity. Tracking would require either caching
     * all xids at the publisher or sending them to subscribers. The condition
     * will resolve naturally once the remaining transactions are finished.
     *
     * Directly advancing the non-removable transaction ID is possible if
     * there are no activities on the publisher since the last advancement
     * cycle. However, it requires maintaining two fields, last_remote_nextxid
     * and last_remote_lsn, within the structure for comparison with the
     * current cycle's values. Considering the minimal cost of continuing in
     * RDT_WAIT_FOR_LOCAL_FLUSH without awaiting changes, we opted not to
     * advance the transaction ID here.
     */
    if (FullTransactionIdPrecedesOrEquals(rdt_data->remote_wait_for,
                                          rdt_data->remote_oldestxid))
        rdt_data->phase = RDT_WAIT_FOR_LOCAL_FLUSH;
    else
        rdt_data->phase = RDT_REQUEST_PUBLISHER_STATUS;
 
    /* process the next phase */
    process_rdt_phase_transition(rdt_data, false);
}
 
/*
 * Workhorse for the RDT_WAIT_FOR_LOCAL_FLUSH phase.
 */
static void
wait_for_local_flush(RetainDeadTuplesData *rdt_data)
{
    Assert(!XLogRecPtrIsInvalid(rdt_data->remote_lsn) &&
           TransactionIdIsValid(rdt_data->candidate_xid));
 
    /*
     * We expect the publisher and subscriber clocks to be in sync using time
     * sync service like NTP. Otherwise, we will advance this worker's
     * oldest_nonremovable_xid prematurely, leading to the removal of rows
     * required to detect update_deleted reliably. This check primarily
     * addresses scenarios where the publisher's clock falls behind; if the
     * publisher's clock is ahead, subsequent transactions will naturally bear
     * later commit timestamps, conforming to the design outlined atop
     * worker.c.
     *
     * XXX Consider waiting for the publisher's clock to catch up with the
     * subscriber's before proceeding to the next phase.
     */
    if (TimestampDifferenceExceeds(rdt_data->reply_time,
                                   rdt_data->candidate_xid_time, 0))
        ereport(ERROR,
                errmsg_internal("oldest_nonremovable_xid transaction ID could be advanced prematurely"),
                errdetail_internal("The clock on the publisher is behind that of the subscriber."));
 
    /*
     * Do not attempt to advance the non-removable transaction ID when table
     * sync is in progress. During this time, changes from a single
     * transaction may be applied by multiple table sync workers corresponding
     * to the target tables. So, it's necessary for all table sync workers to
     * apply and flush the corresponding changes before advancing the
     * transaction ID, otherwise, dead tuples that are still needed for
     * conflict detection in table sync workers could be removed prematurely.
     * However, confirming the apply and flush progress across all table sync
     * workers is complex and not worth the effort, so we simply return if not
     * all tables are in the READY state.
     *
     * Advancing the transaction ID is necessary even when no tables are
     * currently subscribed, to avoid retaining dead tuples unnecessarily.
     * While it might seem safe to skip all phases and directly assign
     * candidate_xid to oldest_nonremovable_xid during the
     * RDT_GET_CANDIDATE_XID phase in such cases, this is unsafe. If users
     * concurrently add tables to the subscription, the apply worker may not
     * process invalidations in time. Consequently,
     * HasSubscriptionRelationsCached() might miss the new tables, leading to
     * premature advancement of oldest_nonremovable_xid.
     *
     * Performing the check during RDT_WAIT_FOR_LOCAL_FLUSH is safe, as
     * invalidations are guaranteed to be processed before applying changes
     * from newly added tables while waiting for the local flush to reach
     * remote_lsn.
     *
     * Additionally, even if we check for subscription tables during
     * RDT_GET_CANDIDATE_XID, they might be dropped before reaching
     * RDT_WAIT_FOR_LOCAL_FLUSH. Therefore, it's still necessary to verify
     * subscription tables at this stage to prevent unnecessary tuple
     * retention.
     */
    if (HasSubscriptionRelationsCached() && !AllTablesyncsReady())
    {
        TimestampTz now;
 
        now = rdt_data->last_recv_time
            ? rdt_data->last_recv_time : GetCurrentTimestamp();
 
        /*
         * Record the time spent waiting for table sync, it is needed for the
         * timeout check in should_stop_conflict_info_retention().
         */
        rdt_data->table_sync_wait_time =
            TimestampDifferenceMilliseconds(rdt_data->candidate_xid_time, now);
 
        return;
    }
 
    /*
     * We don't need to maintain oldest_nonremovable_xid if we decide to stop
     * retaining conflict information for this worker.
     */
    if (should_stop_conflict_info_retention(rdt_data))
    {
        rdt_data->phase = RDT_STOP_CONFLICT_INFO_RETENTION;
        return;
    }
 
    /*
     * Update and check the remote flush position if we are applying changes
     * in a loop. This is done at most once per WalWriterDelay to avoid
     * performing costly operations in get_flush_position() too frequently
     * during change application.
     */
    if (last_flushpos < rdt_data->remote_lsn && rdt_data->last_recv_time &&
        TimestampDifferenceExceeds(rdt_data->flushpos_update_time,
                                   rdt_data->last_recv_time, WalWriterDelay))
    {
        XLogRecPtr  writepos;
        XLogRecPtr  flushpos;
        bool        have_pending_txes;
 
        /* Fetch the latest remote flush position */
        get_flush_position(&writepos, &flushpos, &have_pending_txes);
 
        if (flushpos > last_flushpos)
            last_flushpos = flushpos;
 
        rdt_data->flushpos_update_time = rdt_data->last_recv_time;
    }
 
    /* Return to wait for the changes to be applied */
    if (last_flushpos < rdt_data->remote_lsn)
        return;
 
    /*
     * Reaching this point implies should_stop_conflict_info_retention()
     * returned false earlier, meaning that the most recent duration for
     * advancing the non-removable transaction ID is within the
     * max_retention_duration or max_retention_duration is set to 0.
     *
     * Therefore, if conflict info retention was previously stopped due to a
     * timeout, it is now safe to resume retention.
     */
    if (!MySubscription->retentionactive)
    {
        rdt_data->phase = RDT_RESUME_CONFLICT_INFO_RETENTION;
        return;
    }
 
    /*
     * Reaching here means the remote WAL position has been received, and all
     * transactions up to that position on the publisher have been applied and
     * flushed locally. So, we can advance the non-removable transaction ID.
     */
    SpinLockAcquire(&MyLogicalRepWorker->relmutex);
    MyLogicalRepWorker->oldest_nonremovable_xid = rdt_data->candidate_xid;
    SpinLockRelease(&MyLogicalRepWorker->relmutex);
 
    elog(DEBUG2, "confirmed flush up to remote lsn %X/%08X: new oldest_nonremovable_xid %u",
         LSN_FORMAT_ARGS(rdt_data->remote_lsn),
         rdt_data->candidate_xid);
 
    /* Notify launcher to update the xmin of the conflict slot */
    ApplyLauncherWakeup();
 
    reset_retention_data_fields(rdt_data);
 
    /* process the next phase */
    process_rdt_phase_transition(rdt_data, false);
}
 
/*
 * Check whether conflict information retention should be stopped due to
 * exceeding the maximum wait time (max_retention_duration).
 *
 * If retention should be stopped, return true. Otherwise, return false.
 */
static bool
should_stop_conflict_info_retention(RetainDeadTuplesData *rdt_data)
{
    TimestampTz now;
 
    Assert(TransactionIdIsValid(rdt_data->candidate_xid));
    Assert(rdt_data->phase == RDT_WAIT_FOR_PUBLISHER_STATUS ||
           rdt_data->phase == RDT_WAIT_FOR_LOCAL_FLUSH);
 
    if (!MySubscription->maxretention)
        return false;
 
    /*
     * Use last_recv_time when applying changes in the loop to avoid
     * unnecessary system time retrieval. If last_recv_time is not available,
     * obtain the current timestamp.
     */
    now = rdt_data->last_recv_time ? rdt_data->last_recv_time : GetCurrentTimestamp();
 
    /*
     * Return early if the wait time has not exceeded the configured maximum
     * (max_retention_duration). Time spent waiting for table synchronization
     * is excluded from this calculation, as it occurs infrequently.
     */
    if (!TimestampDifferenceExceeds(rdt_data->candidate_xid_time, now,
                                    MySubscription->maxretention +
                                    rdt_data->table_sync_wait_time))
        return false;
 
    return true;
}
 
/*
 * Workhorse for the RDT_STOP_CONFLICT_INFO_RETENTION phase.
 */
static void
stop_conflict_info_retention(RetainDeadTuplesData *rdt_data)
{
    /* Stop retention if not yet */
    if (MySubscription->retentionactive)
    {
        /*
         * If the retention status cannot be updated (e.g., due to active
         * transaction), skip further processing to avoid inconsistent
         * retention behavior.
         */
        if (!update_retention_status(false))
            return;
 
        SpinLockAcquire(&MyLogicalRepWorker->relmutex);
        MyLogicalRepWorker->oldest_nonremovable_xid = InvalidTransactionId;
        SpinLockRelease(&MyLogicalRepWorker->relmutex);
 
        ereport(LOG,
                errmsg("logical replication worker for subscription \"%s\" has stopped retaining the information for detecting conflicts",
                       MySubscription->name),
                errdetail("Retention is stopped because the apply process has not caught up with the publisher within the configured max_retention_duration."));
    }
 
    Assert(!TransactionIdIsValid(MyLogicalRepWorker->oldest_nonremovable_xid));
 
    /*
     * If retention has been stopped, reset to the initial phase to retry
     * resuming retention. This reset is required to recalculate the current
     * wait time and resume retention if the time falls within
     * max_retention_duration.
     */
    reset_retention_data_fields(rdt_data);
}
 
/*
 * Workhorse for the RDT_RESUME_CONFLICT_INFO_RETENTION phase.
 */
static void
resume_conflict_info_retention(RetainDeadTuplesData *rdt_data)
{
    /* We can't resume retention without updating retention status. */
    if (!update_retention_status(true))
        return;
 
    ereport(LOG,
            errmsg("logical replication worker for subscription \"%s\" will resume retaining the information for detecting conflicts",
                   MySubscription->name),
            MySubscription->maxretention
            ? errdetail("Retention is re-enabled because the apply process has caught up with the publisher within the configured max_retention_duration.")
            : errdetail("Retention is re-enabled because max_retention_duration has been set to unlimited."));
 
    /*
     * Restart the worker to let the launcher initialize
     * oldest_nonremovable_xid at startup.
     *
     * While it's technically possible to derive this value on-the-fly using
     * the conflict detection slot's xmin, doing so risks a race condition:
     * the launcher might clean slot.xmin just after retention resumes. This
     * would make oldest_nonremovable_xid unreliable, especially during xid
     * wraparound.
     *
     * Although this can be prevented by introducing heavy weight locking, the
     * complexity it will bring doesn't seem worthwhile given how rarely
     * retention is resumed.
     */
    apply_worker_exit();
}
 
/*
 * Updates pg_subscription.subretentionactive to the given value within a
 * new transaction.
 *
 * If already inside an active transaction, skips the update and returns
 * false.
 *
 * Returns true if the update is successfully performed.
 */
static bool
update_retention_status(bool active)
{
    /*
     * Do not update the catalog during an active transaction. The transaction
     * may be started during change application, leading to a possible
     * rollback of catalog updates if the application fails subsequently.
     */
    if (IsTransactionState())
        return false;
 
    StartTransactionCommand();
 
    /*
     * Updating pg_subscription might involve TOAST table access, so ensure we
     * have a valid snapshot.
     */
    PushActiveSnapshot(GetTransactionSnapshot());
 
    /* Update pg_subscription.subretentionactive */
    UpdateDeadTupleRetentionStatus(MySubscription->oid, active);
 
    PopActiveSnapshot();
    CommitTransactionCommand();
 
    /* Notify launcher to update the conflict slot */
    ApplyLauncherWakeup();
 
    MySubscription->retentionactive = active;
 
    return true;
}
 
/*
 * Reset all data fields of RetainDeadTuplesData except those used to
 * determine the timing for the next round of transaction ID advancement. We
 * can even use flushpos_update_time in the next round to decide whether to get
 * the latest flush position.
 */
static void
reset_retention_data_fields(RetainDeadTuplesData *rdt_data)
{
    rdt_data->phase = RDT_GET_CANDIDATE_XID;
    rdt_data->remote_lsn = InvalidXLogRecPtr;
    rdt_data->remote_oldestxid = InvalidFullTransactionId;
    rdt_data->remote_nextxid = InvalidFullTransactionId;
    rdt_data->reply_time = 0;
    rdt_data->remote_wait_for = InvalidFullTransactionId;
    rdt_data->candidate_xid = InvalidTransactionId;
    rdt_data->table_sync_wait_time = 0;
}
 
/*
 * Adjust the interval for advancing non-removable transaction IDs.
 *
 * If there is no activity on the node or retention has been stopped, we
 * progressively double the interval used to advance non-removable transaction
 * ID. This helps conserve CPU and network resources when there's little benefit
 * to frequent updates.
 *
 * The interval is capped by the lowest of the following:
 * - wal_receiver_status_interval (if set and retention is active),
 * - a default maximum of 3 minutes,
 * - max_retention_duration (if retention is active).
 *
 * This ensures the interval never exceeds the retention boundary, even if other
 * limits are higher. Once activity resumes on the node and the retention is
 * active, the interval is reset to lesser of 100ms and max_retention_duration,
 * allowing timely advancement of non-removable transaction ID.
 *
 * XXX The use of wal_receiver_status_interval is a bit arbitrary so we can
 * consider the other interval or a separate GUC if the need arises.
 */
static void
adjust_xid_advance_interval(RetainDeadTuplesData *rdt_data, bool new_xid_found)
{
    if (rdt_data->xid_advance_interval && !new_xid_found)
    {
        int         max_interval = wal_receiver_status_interval
            ? wal_receiver_status_interval * 1000
            : MAX_XID_ADVANCE_INTERVAL;
 
        /*
         * No new transaction ID has been assigned since the last check, so
         * double the interval, but not beyond the maximum allowable value.
         */
        rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval * 2,
                                             max_interval);
    }
    else if (rdt_data->xid_advance_interval &&
             !MySubscription->retentionactive)
    {
        /*
         * Retention has been stopped, so double the interval-capped at a
         * maximum of 3 minutes. The wal_receiver_status_interval is
         * intentionally not used as a upper bound, since the likelihood of
         * retention resuming is lower than that of general activity resuming.
         */
        rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval * 2,
                                             MAX_XID_ADVANCE_INTERVAL);
    }
    else
    {
        /*
         * A new transaction ID was found or the interval is not yet
         * initialized, so set the interval to the minimum value.
         */
        rdt_data->xid_advance_interval = MIN_XID_ADVANCE_INTERVAL;
    }
 
    /*
     * Ensure the wait time remains within the maximum retention time limit
     * when retention is active.
     */
    if (MySubscription->retentionactive)
        rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval,
                                             MySubscription->maxretention);
}
 
/*
 * Exit routine for apply workers due to subscription parameter changes.
 */
static void
apply_worker_exit(void)
{
    if (am_parallel_apply_worker())
    {
        /*
         * Don't stop the parallel apply worker as the leader will detect the
         * subscription parameter change and restart logical replication later
         * anyway. This also prevents the leader from reporting errors when
         * trying to communicate with a stopped parallel apply worker, which
         * would accidentally disable subscriptions if disable_on_error was
         * set.
         */
        return;
    }
 
    /*
     * Reset the last-start time for this apply worker so that the launcher
     * will restart it without waiting for wal_retrieve_retry_interval if the
     * subscription is still active, and so that we won't leak that hash table
     * entry if it isn't.
     */
    if (am_leader_apply_worker())
        ApplyLauncherForgetWorkerStartTime(MyLogicalRepWorker->subid);
 
    proc_exit(0);
}
 
/*
 * Reread subscription info if needed.
 *
 * For significant changes, we react by exiting the current process; a new
 * one will be launched afterwards if needed.
 */
void
maybe_reread_subscription(void)
{
    MemoryContext oldctx;
    Subscription *newsub;
    bool        started_tx = false;
 
    /* When cache state is valid there is nothing to do here. */
    if (MySubscriptionValid)
        return;
 
    /* This function might be called inside or outside of transaction. */
    if (!IsTransactionState())
    {
        StartTransactionCommand();
        started_tx = true;
    }
 
    /* Ensure allocations in permanent context. */
    oldctx = MemoryContextSwitchTo(ApplyContext);
 
    newsub = GetSubscription(MyLogicalRepWorker->subid, true);
 
    /*
     * Exit if the subscription was removed. This normally should not happen
     * as the worker gets killed during DROP SUBSCRIPTION.
     */
    if (!newsub)
    {
        ereport(LOG,
                (errmsg("logical replication worker for subscription \"%s\" will stop because the subscription was removed",
                        MySubscription->name)));
 
        /* Ensure we remove no-longer-useful entry for worker's start time */
        if (am_leader_apply_worker())
            ApplyLauncherForgetWorkerStartTime(MyLogicalRepWorker->subid);
 
        proc_exit(0);
    }
 
    /* Exit if the subscription was disabled. */
    if (!newsub->enabled)
    {
        ereport(LOG,
                (errmsg("logical replication worker for subscription \"%s\" will stop because the subscription was disabled",
                        MySubscription->name)));
 
        apply_worker_exit();
    }
 
    /* !slotname should never happen when enabled is true. */
    Assert(newsub->slotname);
 
    /* two-phase cannot be altered while the worker is running */
    Assert(newsub->twophasestate == MySubscription->twophasestate);
 
    /*
     * Exit if any parameter that affects the remote connection was changed.
     * The launcher will start a new worker but note that the parallel apply
     * worker won't restart if the streaming option's value is changed from
     * 'parallel' to any other value or the server decides not to stream the
     * in-progress transaction.
     */
    if (strcmp(newsub->conninfo, MySubscription->conninfo) != 0 ||
        strcmp(newsub->name, MySubscription->name) != 0 ||
        strcmp(newsub->slotname, MySubscription->slotname) != 0 ||
        newsub->binary != MySubscription->binary ||
        newsub->stream != MySubscription->stream ||
        newsub->passwordrequired != MySubscription->passwordrequired ||
        strcmp(newsub->origin, MySubscription->origin) != 0 ||
        newsub->owner != MySubscription->owner ||
        !equal(newsub->publications, MySubscription->publications))
    {
        if (am_parallel_apply_worker())
            ereport(LOG,
                    (errmsg("logical replication parallel apply worker for subscription \"%s\" will stop because of a parameter change",
                            MySubscription->name)));
        else
            ereport(LOG,
                    (errmsg("logical replication worker for subscription \"%s\" will restart because of a parameter change",
                            MySubscription->name)));
 
        apply_worker_exit();
    }
 
    /*
     * Exit if the subscription owner's superuser privileges have been
     * revoked.
     */
    if (!newsub->ownersuperuser && MySubscription->ownersuperuser)
    {
        if (am_parallel_apply_worker())
            ereport(LOG,
                    errmsg("logical replication parallel apply worker for subscription \"%s\" will stop because the subscription owner's superuser privileges have been revoked",
                           MySubscription->name));
        else
            ereport(LOG,
                    errmsg("logical replication worker for subscription \"%s\" will restart because the subscription owner's superuser privileges have been revoked",
                           MySubscription->name));
 
        apply_worker_exit();
    }
 
    /* Check for other changes that should never happen too. */
    if (newsub->dbid != MySubscription->dbid)
    {
        elog(ERROR, "subscription %u changed unexpectedly",
             MyLogicalRepWorker->subid);
    }
 
    /* Clean old subscription info and switch to new one. */
    FreeSubscription(MySubscription);
    MySubscription = newsub;
 
    MemoryContextSwitchTo(oldctx);
 
    /* Change synchronous commit according to the user's wishes */
    SetConfigOption("synchronous_commit", MySubscription->synccommit,
                    PGC_BACKEND, PGC_S_OVERRIDE);
 
    if (started_tx)
        CommitTransactionCommand();
 
    MySubscriptionValid = true;
}
 
/*
 * Callback from subscription syscache invalidation.
 */
static void
subscription_change_cb(Datum arg, int cacheid, uint32 hashvalue)
{
    MySubscriptionValid = false;
}
 
/*
 * subxact_info_write
 *    Store information about subxacts for a toplevel transaction.
 *
 * For each subxact we store offset of its first change in the main file.
 * The file is always over-written as a whole.
 *
 * XXX We should only store subxacts that were not aborted yet.
 */
static void
subxact_info_write(Oid subid, TransactionId xid)
{
    char        path[MAXPGPATH];
    Size        len;
    BufFile    *fd;
 
    Assert(TransactionIdIsValid(xid));
 
    /* construct the subxact filename */
    subxact_filename(path, subid, xid);
 
    /* Delete the subxacts file, if exists. */
    if (subxact_data.nsubxacts == 0)
    {
        cleanup_subxact_info();
        BufFileDeleteFileSet(MyLogicalRepWorker->stream_fileset, path, true);
 
        return;
    }
 
    /*
     * Create the subxact file if it not already created, otherwise open the
     * existing file.
     */
    fd = BufFileOpenFileSet(MyLogicalRepWorker->stream_fileset, path, O_RDWR,
                            true);
    if (fd == NULL)
        fd = BufFileCreateFileSet(MyLogicalRepWorker->stream_fileset, path);
 
    len = sizeof(SubXactInfo) * subxact_data.nsubxacts;
 
    /* Write the subxact count and subxact info */
    BufFileWrite(fd, &subxact_data.nsubxacts, sizeof(subxact_data.nsubxacts));
    BufFileWrite(fd, subxact_data.subxacts, len);
 
    BufFileClose(fd);
 
    /* free the memory allocated for subxact info */
    cleanup_subxact_info();
}
 
/*
 * subxact_info_read
 *    Restore information about subxacts of a streamed transaction.
 *
 * Read information about subxacts into the structure subxact_data that can be
 * used later.
 */
static void
subxact_info_read(Oid subid, TransactionId xid)
{
    char        path[MAXPGPATH];
    Size        len;
    BufFile    *fd;
    MemoryContext oldctx;
 
    Assert(!subxact_data.subxacts);
    Assert(subxact_data.nsubxacts == 0);
    Assert(subxact_data.nsubxacts_max == 0);
 
    /*
     * If the subxact file doesn't exist that means we don't have any subxact
     * info.
     */
    subxact_filename(path, subid, xid);
    fd = BufFileOpenFileSet(MyLogicalRepWorker->stream_fileset, path, O_RDONLY,
                            true);
    if (fd == NULL)
        return;
 
    /* read number of subxact items */
    BufFileReadExact(fd, &subxact_data.nsubxacts, sizeof(subxact_data.nsubxacts));
 
    len = sizeof(SubXactInfo) * subxact_data.nsubxacts;
 
    /* we keep the maximum as a power of 2 */
    subxact_data.nsubxacts_max = 1 << pg_ceil_log2_32(subxact_data.nsubxacts);
 
    /*
     * Allocate subxact information in the logical streaming context. We need
     * this information during the complete stream so that we can add the sub
     * transaction info to this. On stream stop we will flush this information
     * to the subxact file and reset the logical streaming context.
     */
    oldctx = MemoryContextSwitchTo(LogicalStreamingContext);
    subxact_data.subxacts = palloc(subxact_data.nsubxacts_max *
                                   sizeof(SubXactInfo));
    MemoryContextSwitchTo(oldctx);
 
    if (len > 0)
        BufFileReadExact(fd, subxact_data.subxacts, len);
 
    BufFileClose(fd);
}
 
/*
 * subxact_info_add
 *    Add information about a subxact (offset in the main file).
 */
static void
subxact_info_add(TransactionId xid)
{
    SubXactInfo *subxacts = subxact_data.subxacts;
    int64       i;
 
    /* We must have a valid top level stream xid and a stream fd. */
    Assert(TransactionIdIsValid(stream_xid));
    Assert(stream_fd != NULL);
 
    /*
     * If the XID matches the toplevel transaction, we don't want to add it.
     */
    if (stream_xid == xid)
        return;
 
    /*
     * In most cases we're checking the same subxact as we've already seen in
     * the last call, so make sure to ignore it (this change comes later).
     */
    if (subxact_data.subxact_last == xid)
        return;
 
    /* OK, remember we're processing this XID. */
    subxact_data.subxact_last = xid;
 
    /*
     * Check if the transaction is already present in the array of subxact. We
     * intentionally scan the array from the tail, because we're likely adding
     * a change for the most recent subtransactions.
     *
     * XXX Can we rely on the subxact XIDs arriving in sorted order? That
     * would allow us to use binary search here.
     */
    for (i = subxact_data.nsubxacts; i > 0; i--)
    {
        /* found, so we're done */
        if (subxacts[i - 1].xid == xid)
            return;
    }
 
    /* This is a new subxact, so we need to add it to the array. */
    if (subxact_data.nsubxacts == 0)
    {
        MemoryContext oldctx;
 
        subxact_data.nsubxacts_max = 128;
 
        /*
         * Allocate this memory for subxacts in per-stream context, see
         * subxact_info_read.
         */
        oldctx = MemoryContextSwitchTo(LogicalStreamingContext);
        subxacts = palloc(subxact_data.nsubxacts_max * sizeof(SubXactInfo));
        MemoryContextSwitchTo(oldctx);
    }
    else if (subxact_data.nsubxacts == subxact_data.nsubxacts_max)
    {
        subxact_data.nsubxacts_max *= 2;
        subxacts = repalloc(subxacts,
                            subxact_data.nsubxacts_max * sizeof(SubXactInfo));
    }
 
    subxacts[subxact_data.nsubxacts].xid = xid;
 
    /*
     * Get the current offset of the stream file and store it as offset of
     * this subxact.
     */
    BufFileTell(stream_fd,
                &subxacts[subxact_data.nsubxacts].fileno,
                &subxacts[subxact_data.nsubxacts].offset);
 
    subxact_data.nsubxacts++;
    subxact_data.subxacts = subxacts;
}
 
/* format filename for file containing the info about subxacts */
static inline void
subxact_filename(char *path, Oid subid, TransactionId xid)
{
    snprintf(path, MAXPGPATH, "%u-%u.subxacts", subid, xid);
}
 
/* format filename for file containing serialized changes */
static inline void
changes_filename(char *path, Oid subid, TransactionId xid)
{
    snprintf(path, MAXPGPATH, "%u-%u.changes", subid, xid);
}
 
/*
 * stream_cleanup_files
 *    Cleanup files for a subscription / toplevel transaction.
 *
 * Remove files with serialized changes and subxact info for a particular
 * toplevel transaction. Each subscription has a separate set of files
 * for any toplevel transaction.
 */
void
stream_cleanup_files(Oid subid, TransactionId xid)
{
    char        path[MAXPGPATH];
 
    /* Delete the changes file. */
    changes_filename(path, subid, xid);
    BufFileDeleteFileSet(MyLogicalRepWorker->stream_fileset, path, false);
 
    /* Delete the subxact file, if it exists. */
    subxact_filename(path, subid, xid);
    BufFileDeleteFileSet(MyLogicalRepWorker->stream_fileset, path, true);
}
 
/*
 * stream_open_file
 *    Open a file that we'll use to serialize changes for a toplevel
 * transaction.
 *
 * Open a file for streamed changes from a toplevel transaction identified
 * by stream_xid (global variable). If it's the first chunk of streamed
 * changes for this transaction, create the buffile, otherwise open the
 * previously created file.
 */
static void
stream_open_file(Oid subid, TransactionId xid, bool first_segment)
{
    char        path[MAXPGPATH];
    MemoryContext oldcxt;
 
    Assert(OidIsValid(subid));
    Assert(TransactionIdIsValid(xid));
    Assert(stream_fd == NULL);
 
 
    changes_filename(path, subid, xid);
    elog(DEBUG1, "opening file \"%s\" for streamed changes", path);
 
    /*
     * Create/open the buffiles under the logical streaming context so that we
     * have those files until stream stop.
     */
    oldcxt = MemoryContextSwitchTo(LogicalStreamingContext);
 
    /*
     * If this is the first streamed segment, create the changes file.
     * Otherwise, just open the file for writing, in append mode.
     */
    if (first_segment)
        stream_fd = BufFileCreateFileSet(MyLogicalRepWorker->stream_fileset,
                                         path);
    else
    {
        /*
         * Open the file and seek to the end of the file because we always
         * append the changes file.
         */
        stream_fd = BufFileOpenFileSet(MyLogicalRepWorker->stream_fileset,
                                       path, O_RDWR, false);
        BufFileSeek(stream_fd, 0, 0, SEEK_END);
    }
 
    MemoryContextSwitchTo(oldcxt);
}
 
/*
 * stream_close_file
 *    Close the currently open file with streamed changes.
 */
static void
stream_close_file(void)
{
    Assert(stream_fd != NULL);
 
    BufFileClose(stream_fd);
 
    stream_fd = NULL;
}
 
/*
 * stream_write_change
 *    Serialize a change to a file for the current toplevel transaction.
 *
 * The change is serialized in a simple format, with length (not including
 * the length), action code (identifying the message type) and message
 * contents (without the subxact TransactionId value).
 */
static void
stream_write_change(char action, StringInfo s)
{
    int         len;
 
    Assert(stream_fd != NULL);
 
    /* total on-disk size, including the action type character */
    len = (s->len - s->cursor) + sizeof(char);
 
    /* first write the size */
    BufFileWrite(stream_fd, &len, sizeof(len));
 
    /* then the action */
    BufFileWrite(stream_fd, &action, sizeof(action));
 
    /* and finally the remaining part of the buffer (after the XID) */
    len = (s->len - s->cursor);
 
    BufFileWrite(stream_fd, &s->data[s->cursor], len);
}
 
/*
 * stream_open_and_write_change
 *    Serialize a message to a file for the given transaction.
 *
 * This function is similar to stream_write_change except that it will open the
 * target file if not already before writing the message and close the file at
 * the end.
 */
static void
stream_open_and_write_change(TransactionId xid, char action, StringInfo s)
{
    Assert(!in_streamed_transaction);
 
    if (!stream_fd)
        stream_start_internal(xid, false);
 
    stream_write_change(action, s);
    stream_stop_internal(xid);
}
 
/*
 * Sets streaming options including replication slot name and origin start
 * position. Workers need these options for logical replication.
 */
void
set_stream_options(WalRcvStreamOptions *options,
                   char *slotname,
                   XLogRecPtr *origin_startpos)
{
    int         server_version;
 
    options->logical = true;
    options->startpoint = *origin_startpos;
    options->slotname = slotname;
 
    server_version = walrcv_server_version(LogRepWorkerWalRcvConn);
    options->proto.logical.proto_version =
        server_version >= 160000 ? LOGICALREP_PROTO_STREAM_PARALLEL_VERSION_NUM :
        server_version >= 150000 ? LOGICALREP_PROTO_TWOPHASE_VERSION_NUM :
        server_version >= 140000 ? LOGICALREP_PROTO_STREAM_VERSION_NUM :
        LOGICALREP_PROTO_VERSION_NUM;
 
    options->proto.logical.publication_names = MySubscription->publications;
    options->proto.logical.binary = MySubscription->binary;
 
    /*
     * Assign the appropriate option value for streaming option according to
     * the 'streaming' mode and the publisher's ability to support that mode.
     */
    if (server_version >= 160000 &&
        MySubscription->stream == LOGICALREP_STREAM_PARALLEL)
    {
        options->proto.logical.streaming_str = "parallel";
        MyLogicalRepWorker->parallel_apply = true;
    }
    else if (server_version >= 140000 &&
             MySubscription->stream != LOGICALREP_STREAM_OFF)
    {
        options->proto.logical.streaming_str = "on";
        MyLogicalRepWorker->parallel_apply = false;
    }
    else
    {
        options->proto.logical.streaming_str = NULL;
        MyLogicalRepWorker->parallel_apply = false;
    }
 
    options->proto.logical.twophase = false;
    options->proto.logical.origin = pstrdup(MySubscription->origin);
}
 
/*
 * Cleanup the memory for subxacts and reset the related variables.
 */
static inline void
cleanup_subxact_info()
{
    if (subxact_data.subxacts)
        pfree(subxact_data.subxacts);
 
    subxact_data.subxacts = NULL;
    subxact_data.subxact_last = InvalidTransactionId;
    subxact_data.nsubxacts = 0;
    subxact_data.nsubxacts_max = 0;
}
 
/*
 * Common function to run the apply loop with error handling. Disable the
 * subscription, if necessary.
 *
 * Note that we don't handle FATAL errors which are probably because
 * of system resource error and are not repeatable.
 */
void
start_apply(XLogRecPtr origin_startpos)
{
    PG_TRY();
    {
        LogicalRepApplyLoop(origin_startpos);
    }
    PG_CATCH();
    {
        /*
         * Reset the origin state to prevent the advancement of origin
         * progress if we fail to apply. Otherwise, this will result in
         * transaction loss as that transaction won't be sent again by the
         * server.
         */
        replorigin_reset(0, (Datum) 0);
 
        if (MySubscription->disableonerr)
            DisableSubscriptionAndExit();
        else
        {
            /*
             * Report the worker failed while applying changes. Abort the
             * current transaction so that the stats message is sent in an
             * idle state.
             */
            AbortOutOfAnyTransaction();
            pgstat_report_subscription_error(MySubscription->oid, !am_tablesync_worker());
 
            PG_RE_THROW();
        }
    }
    PG_END_TRY();
}
 
/*
 * Runs the leader apply worker.
 *
 * It sets up replication origin, streaming options and then starts streaming.
 */
static void
run_apply_worker()
{
    char        originname[NAMEDATALEN];
    XLogRecPtr  origin_startpos = InvalidXLogRecPtr;
    char       *slotname = NULL;
    WalRcvStreamOptions options;
    RepOriginId originid;
    TimeLineID  startpointTLI;
    char       *err;
    bool        must_use_password;
 
    slotname = MySubscription->slotname;
 
    /*
     * This shouldn't happen if the subscription is enabled, but guard against
     * DDL bugs or manual catalog changes.  (libpqwalreceiver will crash if
     * slot is NULL.)
     */
    if (!slotname)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("subscription has no replication slot set")));
 
    /* Setup replication origin tracking. */
    ReplicationOriginNameForLogicalRep(MySubscription->oid, InvalidOid,
                                       originname, sizeof(originname));
    StartTransactionCommand();
    originid = replorigin_by_name(originname, true);
    if (!OidIsValid(originid))
        originid = replorigin_create(originname);
    replorigin_session_setup(originid, 0);
    replorigin_session_origin = originid;
    origin_startpos = replorigin_session_get_progress(false);
    CommitTransactionCommand();
 
    /* Is the use of a password mandatory? */
    must_use_password = MySubscription->passwordrequired &&
        !MySubscription->ownersuperuser;
 
    LogRepWorkerWalRcvConn = walrcv_connect(MySubscription->conninfo, true,
                                            true, must_use_password,
                                            MySubscription->name, &err);
 
    if (LogRepWorkerWalRcvConn == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_CONNECTION_FAILURE),
                 errmsg("apply worker for subscription \"%s\" could not connect to the publisher: %s",
                        MySubscription->name, err)));
 
    /*
     * We don't really use the output identify_system for anything but it does
     * some initializations on the upstream so let's still call it.
     */
    (void) walrcv_identify_system(LogRepWorkerWalRcvConn, &startpointTLI);
 
    set_apply_error_context_origin(originname);
 
    set_stream_options(&options, slotname, &origin_startpos);
 
    /*
     * Even when the two_phase mode is requested by the user, it remains as
     * the tri-state PENDING until all tablesyncs have reached READY state.
     * Only then, can it become ENABLED.
     *
     * Note: If the subscription has no tables then leave the state as
     * PENDING, which allows ALTER SUBSCRIPTION ... REFRESH PUBLICATION to
     * work.
     */
    if (MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_PENDING &&
        AllTablesyncsReady())
    {
        /* Start streaming with two_phase enabled */
        options.proto.logical.twophase = true;
        walrcv_startstreaming(LogRepWorkerWalRcvConn, &options);
 
        StartTransactionCommand();
 
        /*
         * Updating pg_subscription might involve TOAST table access, so
         * ensure we have a valid snapshot.
         */
        PushActiveSnapshot(GetTransactionSnapshot());
 
        UpdateTwoPhaseState(MySubscription->oid, LOGICALREP_TWOPHASE_STATE_ENABLED);
        MySubscription->twophasestate = LOGICALREP_TWOPHASE_STATE_ENABLED;
        PopActiveSnapshot();
        CommitTransactionCommand();
    }
    else
    {
        walrcv_startstreaming(LogRepWorkerWalRcvConn, &options);
    }
 
    ereport(DEBUG1,
            (errmsg_internal("logical replication apply worker for subscription \"%s\" two_phase is %s",
                             MySubscription->name,
                             MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_DISABLED ? "DISABLED" :
                             MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_PENDING ? "PENDING" :
                             MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED ? "ENABLED" :
                             "?")));
 
    /* Run the main loop. */
    start_apply(origin_startpos);
}
 
/*
 * Common initialization for leader apply worker, parallel apply worker and
 * tablesync worker.
 *
 * Initialize the database connection, in-memory subscription and necessary
 * config options.
 */
void
InitializeLogRepWorker(void)
{
    MemoryContext oldctx;
 
    /* Run as replica session replication role. */
    SetConfigOption("session_replication_role", "replica",
                    PGC_SUSET, PGC_S_OVERRIDE);
 
    /* Connect to our database. */
    BackgroundWorkerInitializeConnectionByOid(MyLogicalRepWorker->dbid,
                                              MyLogicalRepWorker->userid,
                                              0);
 
    /*
     * Set always-secure search path, so malicious users can't redirect user
     * code (e.g. pg_index.indexprs).
     */
    SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
 
    /* Load the subscription into persistent memory context. */
    ApplyContext = AllocSetContextCreate(TopMemoryContext,
                                         "ApplyContext",
                                         ALLOCSET_DEFAULT_SIZES);
    StartTransactionCommand();
    oldctx = MemoryContextSwitchTo(ApplyContext);
 
    /*
     * Lock the subscription to prevent it from being concurrently dropped,
     * then re-verify its existence. After the initialization, the worker will
     * be terminated gracefully if the subscription is dropped.
     */
    LockSharedObject(SubscriptionRelationId, MyLogicalRepWorker->subid, 0,
                     AccessShareLock);
    MySubscription = GetSubscription(MyLogicalRepWorker->subid, true);
    if (!MySubscription)
    {
        ereport(LOG,
                (errmsg("logical replication worker for subscription %u will not start because the subscription was removed during startup",
                        MyLogicalRepWorker->subid)));
 
        /* Ensure we remove no-longer-useful entry for worker's start time */
        if (am_leader_apply_worker())
            ApplyLauncherForgetWorkerStartTime(MyLogicalRepWorker->subid);
 
        proc_exit(0);
    }
 
    MySubscriptionValid = true;
    MemoryContextSwitchTo(oldctx);
 
    if (!MySubscription->enabled)
    {
        ereport(LOG,
                (errmsg("logical replication worker for subscription \"%s\" will not start because the subscription was disabled during startup",
                        MySubscription->name)));
 
        apply_worker_exit();
    }
 
    /*
     * Restart the worker if retain_dead_tuples was enabled during startup.
     *
     * At this point, the replication slot used for conflict detection might
     * not exist yet, or could be dropped soon if the launcher perceives
     * retain_dead_tuples as disabled. To avoid unnecessary tracking of
     * oldest_nonremovable_xid when the slot is absent or at risk of being
     * dropped, a restart is initiated.
     *
     * The oldest_nonremovable_xid should be initialized only when the
     * subscription's retention is active before launching the worker. See
     * logicalrep_worker_launch.
     */
    if (am_leader_apply_worker() &&
        MySubscription->retaindeadtuples &&
        MySubscription->retentionactive &&
        !TransactionIdIsValid(MyLogicalRepWorker->oldest_nonremovable_xid))
    {
        ereport(LOG,
                errmsg("logical replication worker for subscription \"%s\" will restart because the option %s was enabled during startup",
                       MySubscription->name, "retain_dead_tuples"));
 
        apply_worker_exit();
    }
 
    /* Setup synchronous commit according to the user's wishes */
    SetConfigOption("synchronous_commit", MySubscription->synccommit,
                    PGC_BACKEND, PGC_S_OVERRIDE);
 
    /*
     * Keep us informed about subscription or role changes. Note that the
     * role's superuser privilege can be revoked.
     */
    CacheRegisterSyscacheCallback(SUBSCRIPTIONOID,
                                  subscription_change_cb,
                                  (Datum) 0);
 
    CacheRegisterSyscacheCallback(AUTHOID,
                                  subscription_change_cb,
                                  (Datum) 0);
 
    if (am_tablesync_worker())
        ereport(LOG,
                (errmsg("logical replication table synchronization worker for subscription \"%s\", table \"%s\" has started",
                        MySubscription->name,
                        get_rel_name(MyLogicalRepWorker->relid))));
    else
        ereport(LOG,
                (errmsg("logical replication apply worker for subscription \"%s\" has started",
                        MySubscription->name)));
 
    CommitTransactionCommand();
}
 
/*
 * Reset the origin state.
 */
static void
replorigin_reset(int code, Datum arg)
{
    replorigin_session_origin = InvalidRepOriginId;
    replorigin_session_origin_lsn = InvalidXLogRecPtr;
    replorigin_session_origin_timestamp = 0;
}
 
/* Common function to setup the leader apply or tablesync worker. */
void
SetupApplyOrSyncWorker(int worker_slot)
{
    /* Attach to slot */
    logicalrep_worker_attach(worker_slot);
 
    Assert(am_tablesync_worker() || am_leader_apply_worker());
 
    /* Setup signal handling */
    pqsignal(SIGHUP, SignalHandlerForConfigReload);
    pqsignal(SIGTERM, die);
    BackgroundWorkerUnblockSignals();
 
    /*
     * We don't currently need any ResourceOwner in a walreceiver process, but
     * if we did, we could call CreateAuxProcessResourceOwner here.
     */
 
    /* Initialise stats to a sanish value */
    MyLogicalRepWorker->last_send_time = MyLogicalRepWorker->last_recv_time =
        MyLogicalRepWorker->reply_time = GetCurrentTimestamp();
 
    /* Load the libpq-specific functions */
    load_file("libpqwalreceiver", false);
 
    InitializeLogRepWorker();
 
    /*
     * Register a callback to reset the origin state before aborting any
     * pending transaction during shutdown (see ShutdownPostgres()). This will
     * avoid origin advancement for an in-complete transaction which could
     * otherwise lead to its loss as such a transaction won't be sent by the
     * server again.
     *
     * Note that even a LOG or DEBUG statement placed after setting the origin
     * state may process a shutdown signal before committing the current apply
     * operation. So, it is important to register such a callback here.
     */
    before_shmem_exit(replorigin_reset, (Datum) 0);
 
    /* Connect to the origin and start the replication. */
    elog(DEBUG1, "connecting to publisher using connection string \"%s\"",
         MySubscription->conninfo);
 
    /*
     * Setup callback for syscache so that we know when something changes in
     * the subscription relation state.
     */
    CacheRegisterSyscacheCallback(SUBSCRIPTIONRELMAP,
                                  invalidate_syncing_table_states,
                                  (Datum) 0);
}
 
/* Logical Replication Apply worker entry point */
void
ApplyWorkerMain(Datum main_arg)
{
    int         worker_slot = DatumGetInt32(main_arg);
 
    InitializingApplyWorker = true;
 
    SetupApplyOrSyncWorker(worker_slot);
 
    InitializingApplyWorker = false;
 
    run_apply_worker();
 
    proc_exit(0);
}
 
/*
 * After error recovery, disable the subscription in a new transaction
 * and exit cleanly.
 */
void
DisableSubscriptionAndExit(void)
{
    /*
     * Emit the error message, and recover from the error state to an idle
     * state
     */
    HOLD_INTERRUPTS();
 
    EmitErrorReport();
    AbortOutOfAnyTransaction();
    FlushErrorState();
 
    RESUME_INTERRUPTS();
 
    /* Report the worker failed during either table synchronization or apply */
    pgstat_report_subscription_error(MyLogicalRepWorker->subid,
                                     !am_tablesync_worker());
 
    /* Disable the subscription */
    StartTransactionCommand();
 
    /*
     * Updating pg_subscription might involve TOAST table access, so ensure we
     * have a valid snapshot.
     */
    PushActiveSnapshot(GetTransactionSnapshot());
 
    DisableSubscription(MySubscription->oid);
    PopActiveSnapshot();
    CommitTransactionCommand();
 
    /* Ensure we remove no-longer-useful entry for worker's start time */
    if (am_leader_apply_worker())
        ApplyLauncherForgetWorkerStartTime(MyLogicalRepWorker->subid);
 
    /* Notify the subscription has been disabled and exit */
    ereport(LOG,
            errmsg("subscription \"%s\" has been disabled because of an error",
                   MySubscription->name));
 
    /*
     * Skip the track_commit_timestamp check when disabling the worker due to
     * an error, as verifying commit timestamps is unnecessary in this
     * context.
     */
    CheckSubDeadTupleRetention(false, true, WARNING,
                               MySubscription->retaindeadtuples,
                               MySubscription->retentionactive, false);
 
    proc_exit(0);
}
 
/*
 * Is current process a logical replication worker?
 */
bool
IsLogicalWorker(void)
{
    return MyLogicalRepWorker != NULL;
}
 
/*
 * Is current process a logical replication parallel apply worker?
 */
bool
IsLogicalParallelApplyWorker(void)
{
    return IsLogicalWorker() && am_parallel_apply_worker();
}
 
/*
 * Start skipping changes of the transaction if the given LSN matches the
 * LSN specified by subscription's skiplsn.
 */
static void
maybe_start_skipping_changes(XLogRecPtr finish_lsn)
{
    Assert(!is_skipping_changes());
    Assert(!in_remote_transaction);
    Assert(!in_streamed_transaction);
 
    /*
     * Quick return if it's not requested to skip this transaction. This
     * function is called for every remote transaction and we assume that
     * skipping the transaction is not used often.
     */
    if (likely(XLogRecPtrIsInvalid(MySubscription->skiplsn) ||
               MySubscription->skiplsn != finish_lsn))
        return;
 
    /* Start skipping all changes of this transaction */
    skip_xact_finish_lsn = finish_lsn;
 
    ereport(LOG,
            errmsg("logical replication starts skipping transaction at LSN %X/%08X",
                   LSN_FORMAT_ARGS(skip_xact_finish_lsn)));
}
 
/*
 * Stop skipping changes by resetting skip_xact_finish_lsn if enabled.
 */
static void
stop_skipping_changes(void)
{
    if (!is_skipping_changes())
        return;
 
    ereport(LOG,
            errmsg("logical replication completed skipping transaction at LSN %X/%08X",
                   LSN_FORMAT_ARGS(skip_xact_finish_lsn)));
 
    /* Stop skipping changes */
    skip_xact_finish_lsn = InvalidXLogRecPtr;
}
 
/*
 * Clear subskiplsn of pg_subscription catalog.
 *
 * finish_lsn is the transaction's finish LSN that is used to check if the
 * subskiplsn matches it. If not matched, we raise a warning when clearing the
 * subskiplsn in order to inform users for cases e.g., where the user mistakenly
 * specified the wrong subskiplsn.
 */
static void
clear_subscription_skip_lsn(XLogRecPtr finish_lsn)
{
    Relation    rel;
    Form_pg_subscription subform;
    HeapTuple   tup;
    XLogRecPtr  myskiplsn = MySubscription->skiplsn;
    bool        started_tx = false;
 
    if (likely(XLogRecPtrIsInvalid(myskiplsn)) || am_parallel_apply_worker())
        return;
 
    if (!IsTransactionState())
    {
        StartTransactionCommand();
        started_tx = true;
    }
 
    /*
     * Updating pg_subscription might involve TOAST table access, so ensure we
     * have a valid snapshot.
     */
    PushActiveSnapshot(GetTransactionSnapshot());
 
    /*
     * Protect subskiplsn of pg_subscription from being concurrently updated
     * while clearing it.
     */
    LockSharedObject(SubscriptionRelationId, MySubscription->oid, 0,
                     AccessShareLock);
 
    rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
    /* Fetch the existing tuple. */
    tup = SearchSysCacheCopy1(SUBSCRIPTIONOID,
                              ObjectIdGetDatum(MySubscription->oid));
 
    if (!HeapTupleIsValid(tup))
        elog(ERROR, "subscription \"%s\" does not exist", MySubscription->name);
 
    subform = (Form_pg_subscription) GETSTRUCT(tup);
 
    /*
     * Clear the subskiplsn. If the user has already changed subskiplsn before
     * clearing it we don't update the catalog and the replication origin
     * state won't get advanced. So in the worst case, if the server crashes
     * before sending an acknowledgment of the flush position the transaction
     * will be sent again and the user needs to set subskiplsn again. We can
     * reduce the possibility by logging a replication origin WAL record to
     * advance the origin LSN instead but there is no way to advance the
     * origin timestamp and it doesn't seem to be worth doing anything about
     * it since it's a very rare case.
     */
    if (subform->subskiplsn == myskiplsn)
    {
        bool        nulls[Natts_pg_subscription];
        bool        replaces[Natts_pg_subscription];
        Datum       values[Natts_pg_subscription];
 
        memset(values, 0, sizeof(values));
        memset(nulls, false, sizeof(nulls));
        memset(replaces, false, sizeof(replaces));
 
        /* reset subskiplsn */
        values[Anum_pg_subscription_subskiplsn - 1] = LSNGetDatum(InvalidXLogRecPtr);
        replaces[Anum_pg_subscription_subskiplsn - 1] = true;
 
        tup = heap_modify_tuple(tup, RelationGetDescr(rel), values, nulls,
                                replaces);
        CatalogTupleUpdate(rel, &tup->t_self, tup);
 
        if (myskiplsn != finish_lsn)
            ereport(WARNING,
                    errmsg("skip-LSN of subscription \"%s\" cleared", MySubscription->name),
                    errdetail("Remote transaction's finish WAL location (LSN) %X/%08X did not match skip-LSN %X/%08X.",
                              LSN_FORMAT_ARGS(finish_lsn),
                              LSN_FORMAT_ARGS(myskiplsn)));
    }
 
    heap_freetuple(tup);
    table_close(rel, NoLock);
 
    PopActiveSnapshot();
 
    if (started_tx)
        CommitTransactionCommand();
}
 
/* Error callback to give more context info about the change being applied */
void
apply_error_callback(void *arg)
{
    ApplyErrorCallbackArg *errarg = &apply_error_callback_arg;
 
    if (apply_error_callback_arg.command == 0)
        return;
 
    Assert(errarg->origin_name);
 
    if (errarg->rel == NULL)
    {
        if (!TransactionIdIsValid(errarg->remote_xid))
            errcontext("processing remote data for replication origin \"%s\" during message type \"%s\"",
                       errarg->origin_name,
                       logicalrep_message_type(errarg->command));
        else if (XLogRecPtrIsInvalid(errarg->finish_lsn))
            errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" in transaction %u",
                       errarg->origin_name,
                       logicalrep_message_type(errarg->command),
                       errarg->remote_xid);
        else
            errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" in transaction %u, finished at %X/%08X",
                       errarg->origin_name,
                       logicalrep_message_type(errarg->command),
                       errarg->remote_xid,
                       LSN_FORMAT_ARGS(errarg->finish_lsn));
    }
    else
    {
        if (errarg->remote_attnum < 0)
        {
            if (XLogRecPtrIsInvalid(errarg->finish_lsn))
                errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" in transaction %u",
                           errarg->origin_name,
                           logicalrep_message_type(errarg->command),
                           errarg->rel->remoterel.nspname,
                           errarg->rel->remoterel.relname,
                           errarg->remote_xid);
            else
                errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" in transaction %u, finished at %X/%08X",
                           errarg->origin_name,
                           logicalrep_message_type(errarg->command),
                           errarg->rel->remoterel.nspname,
                           errarg->rel->remoterel.relname,
                           errarg->remote_xid,
                           LSN_FORMAT_ARGS(errarg->finish_lsn));
        }
        else
        {
            if (XLogRecPtrIsInvalid(errarg->finish_lsn))
                errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" column \"%s\" in transaction %u",
                           errarg->origin_name,
                           logicalrep_message_type(errarg->command),
                           errarg->rel->remoterel.nspname,
                           errarg->rel->remoterel.relname,
                           errarg->rel->remoterel.attnames[errarg->remote_attnum],
                           errarg->remote_xid);
            else
                errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" column \"%s\" in transaction %u, finished at %X/%08X",
                           errarg->origin_name,
                           logicalrep_message_type(errarg->command),
                           errarg->rel->remoterel.nspname,
                           errarg->rel->remoterel.relname,
                           errarg->rel->remoterel.attnames[errarg->remote_attnum],
                           errarg->remote_xid,
                           LSN_FORMAT_ARGS(errarg->finish_lsn));
        }
    }
}
 
/* Set transaction information of apply error callback */
static inline void
set_apply_error_context_xact(TransactionId xid, XLogRecPtr lsn)
{
    apply_error_callback_arg.remote_xid = xid;
    apply_error_callback_arg.finish_lsn = lsn;
}
 
/* Reset all information of apply error callback */
static inline void
reset_apply_error_context_info(void)
{
    apply_error_callback_arg.command = 0;
    apply_error_callback_arg.rel = NULL;
    apply_error_callback_arg.remote_attnum = -1;
    set_apply_error_context_xact(InvalidTransactionId, InvalidXLogRecPtr);
}
 
/*
 * Request wakeup of the workers for the given subscription OID
 * at commit of the current transaction.
 *
 * This is used to ensure that the workers process assorted changes
 * as soon as possible.
 */
void
LogicalRepWorkersWakeupAtCommit(Oid subid)
{
    MemoryContext oldcxt;
 
    oldcxt = MemoryContextSwitchTo(TopTransactionContext);
    on_commit_wakeup_workers_subids =
        list_append_unique_oid(on_commit_wakeup_workers_subids, subid);
    MemoryContextSwitchTo(oldcxt);
}
 
/*
 * Wake up the workers of any subscriptions that were changed in this xact.
 */
void
AtEOXact_LogicalRepWorkers(bool isCommit)
{
    if (isCommit && on_commit_wakeup_workers_subids != NIL)
    {
        ListCell   *lc;
 
        LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
        foreach(lc, on_commit_wakeup_workers_subids)
        {
            Oid         subid = lfirst_oid(lc);
            List       *workers;
            ListCell   *lc2;
 
            workers = logicalrep_workers_find(subid, true, false);
            foreach(lc2, workers)
            {
                LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
 
                logicalrep_worker_wakeup_ptr(worker);
            }
        }
        LWLockRelease(LogicalRepWorkerLock);
    }
 
    /* The List storage will be reclaimed automatically in xact cleanup. */
    on_commit_wakeup_workers_subids = NIL;
}
 
/*
 * Allocate the origin name in long-lived context for error context message.
 */
void
set_apply_error_context_origin(char *originname)
{
    apply_error_callback_arg.origin_name = MemoryContextStrdup(ApplyContext,
                                                               originname);
}
 
/*
 * Return the action to be taken for the given transaction. See
 * TransApplyAction for information on each of the actions.
 *
 * *winfo is assigned to the destination parallel worker info when the leader
 * apply worker has to pass all the transaction's changes to the parallel
 * apply worker.
 */
static TransApplyAction
get_transaction_apply_action(TransactionId xid, ParallelApplyWorkerInfo **winfo)
{
    *winfo = NULL;
 
    if (am_parallel_apply_worker())
    {
        return TRANS_PARALLEL_APPLY;
    }
 
    /*
     * If we are processing this transaction using a parallel apply worker
     * then either we send the changes to the parallel worker or if the worker
     * is busy then serialize the changes to the file which will later be
     * processed by the parallel worker.
     */
    *winfo = pa_find_worker(xid);
 
    if (*winfo && (*winfo)->serialize_changes)
    {
        return TRANS_LEADER_PARTIAL_SERIALIZE;
    }
    else if (*winfo)
    {
        return TRANS_LEADER_SEND_TO_PARALLEL;
    }
 
    /*
     * If there is no parallel worker involved to process this transaction
     * then we either directly apply the change or serialize it to a file
     * which will later be applied when the transaction finish message is
     * processed.
     */
    else if (in_streamed_transaction)
    {
        return TRANS_LEADER_SERIALIZE;
    }
    else
    {
        return TRANS_LEADER_APPLY;
    }
}