xact.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * xact.h
 *    postgres transaction system definitions
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/xact.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef XACT_H
#define XACT_H
 
#include "access/transam.h"
#include "access/xlogreader.h"
#include "datatype/timestamp.h"
#include "lib/stringinfo.h"
#include "nodes/pg_list.h"
#include "storage/relfilelocator.h"
#include "storage/sinval.h"
 
/*
 * Maximum size of Global Transaction ID (including '\0').
 *
 * Note that the max value of GIDSIZE must fit in the uint16 gidlen,
 * specified in TwoPhaseFileHeader.
 */
#define GIDSIZE 200
 
/*
 * Xact isolation levels
 */
#define XACT_READ_UNCOMMITTED   0
#define XACT_READ_COMMITTED     1
#define XACT_REPEATABLE_READ    2
#define XACT_SERIALIZABLE       3
 
extern PGDLLIMPORT int DefaultXactIsoLevel;
extern PGDLLIMPORT int XactIsoLevel;
 
/*
 * We implement three isolation levels internally.
 * The weakest uses one snapshot per statement;
 * the two stronger levels use one snapshot per database transaction.
 * Serializable uses predicate locks in addition to the snapshot.
 * These macros can be used to determine which implementation to use
 * depending on the prevailing serialization level.
 */
#define IsolationUsesXactSnapshot() (XactIsoLevel >= XACT_REPEATABLE_READ)
#define IsolationIsSerializable() (XactIsoLevel == XACT_SERIALIZABLE)
 
/* Xact read-only state */
extern PGDLLIMPORT bool DefaultXactReadOnly;
extern PGDLLIMPORT bool XactReadOnly;
 
/* flag for logging statements in this transaction */
extern PGDLLIMPORT bool xact_is_sampled;
 
/*
 * Xact is deferrable -- only meaningful (currently) for read only
 * SERIALIZABLE transactions
 */
extern PGDLLIMPORT bool DefaultXactDeferrable;
extern PGDLLIMPORT bool XactDeferrable;
 
typedef enum
{
    SYNCHRONOUS_COMMIT_OFF,     /* asynchronous commit */
    SYNCHRONOUS_COMMIT_LOCAL_FLUSH, /* wait for local flush only */
    SYNCHRONOUS_COMMIT_REMOTE_WRITE,    /* wait for local flush and remote
                                         * write */
    SYNCHRONOUS_COMMIT_REMOTE_FLUSH,    /* wait for local and remote flush */
    SYNCHRONOUS_COMMIT_REMOTE_APPLY,    /* wait for local and remote flush and
                                         * remote apply */
}           SyncCommitLevel;
 
/* Define the default setting for synchronous_commit */
#define SYNCHRONOUS_COMMIT_ON   SYNCHRONOUS_COMMIT_REMOTE_FLUSH
 
/* Synchronous commit level */
extern PGDLLIMPORT int synchronous_commit;
 
/* used during logical streaming of a transaction */
extern PGDLLIMPORT TransactionId CheckXidAlive;
extern PGDLLIMPORT bool bsysscan;
 
/*
 * Miscellaneous flag bits to record events which occur on the top level
 * transaction. These flags are only persisted in MyXactFlags and are intended
 * so we remember to do certain things later in the transaction. This is
 * globally accessible, so can be set from anywhere in the code which requires
 * recording flags.
 */
extern PGDLLIMPORT int MyXactFlags;
 
/*
 * XACT_FLAGS_ACCESSEDTEMPNAMESPACE - set when a temporary object is accessed.
 * We don't allow PREPARE TRANSACTION in that case.
 */
#define XACT_FLAGS_ACCESSEDTEMPNAMESPACE        (1U << 0)
 
/*
 * XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK - records whether the top level xact
 * logged any Access Exclusive Locks.
 */
#define XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK  (1U << 1)
 
/*
 * XACT_FLAGS_NEEDIMMEDIATECOMMIT - records whether the top level statement
 * is one that requires immediate commit, such as CREATE DATABASE.
 */
#define XACT_FLAGS_NEEDIMMEDIATECOMMIT          (1U << 2)
 
/*
 * XACT_FLAGS_PIPELINING - set when we complete an extended-query-protocol
 * Execute message.  This is useful for detecting that an implicit transaction
 * block has been created via pipelining.
 */
#define XACT_FLAGS_PIPELINING                   (1U << 3)
 
/*
 *  start- and end-of-transaction callbacks for dynamically loaded modules
 */
typedef enum
{
    XACT_EVENT_COMMIT,
    XACT_EVENT_PARALLEL_COMMIT,
    XACT_EVENT_ABORT,
    XACT_EVENT_PARALLEL_ABORT,
    XACT_EVENT_PREPARE,
    XACT_EVENT_PRE_COMMIT,
    XACT_EVENT_PARALLEL_PRE_COMMIT,
    XACT_EVENT_PRE_PREPARE,
} XactEvent;
 
typedef void (*XactCallback) (XactEvent event, void *arg);
 
typedef enum
{
    SUBXACT_EVENT_START_SUB,
    SUBXACT_EVENT_COMMIT_SUB,
    SUBXACT_EVENT_ABORT_SUB,
    SUBXACT_EVENT_PRE_COMMIT_SUB,
} SubXactEvent;
 
typedef void (*SubXactCallback) (SubXactEvent event, SubTransactionId mySubid,
                                 SubTransactionId parentSubid, void *arg);
 
/* Data structure for Save/RestoreTransactionCharacteristics */
typedef struct SavedTransactionCharacteristics
{
    int         save_XactIsoLevel;
    bool        save_XactReadOnly;
    bool        save_XactDeferrable;
} SavedTransactionCharacteristics;
 
 
/* ----------------
 *      transaction-related XLOG entries
 * ----------------
 */
 
/*
 * XLOG allows to store some information in high 4 bits of log record xl_info
 * field. We use 3 for the opcode, and one about an optional flag variable.
 */
#define XLOG_XACT_COMMIT            0x00
#define XLOG_XACT_PREPARE           0x10
#define XLOG_XACT_ABORT             0x20
#define XLOG_XACT_COMMIT_PREPARED   0x30
#define XLOG_XACT_ABORT_PREPARED    0x40
#define XLOG_XACT_ASSIGNMENT        0x50
#define XLOG_XACT_INVALIDATIONS     0x60
/* free opcode 0x70 */
 
/* mask for filtering opcodes out of xl_info */
#define XLOG_XACT_OPMASK            0x70
 
/* does this record have a 'xinfo' field or not */
#define XLOG_XACT_HAS_INFO          0x80
 
/*
 * The following flags, stored in xinfo, determine which information is
 * contained in commit/abort records.
 */
#define XACT_XINFO_HAS_DBINFO           (1U << 0)
#define XACT_XINFO_HAS_SUBXACTS         (1U << 1)
#define XACT_XINFO_HAS_RELFILELOCATORS  (1U << 2)
#define XACT_XINFO_HAS_INVALS           (1U << 3)
#define XACT_XINFO_HAS_TWOPHASE         (1U << 4)
#define XACT_XINFO_HAS_ORIGIN           (1U << 5)
#define XACT_XINFO_HAS_AE_LOCKS         (1U << 6)
#define XACT_XINFO_HAS_GID              (1U << 7)
#define XACT_XINFO_HAS_DROPPED_STATS    (1U << 8)
 
/*
 * Also stored in xinfo, these indicating a variety of additional actions that
 * need to occur when emulating transaction effects during recovery.
 *
 * They are named XactCompletion... to differentiate them from
 * EOXact... routines which run at the end of the original transaction
 * completion.
 */
#define XACT_COMPLETION_APPLY_FEEDBACK          (1U << 29)
#define XACT_COMPLETION_UPDATE_RELCACHE_FILE    (1U << 30)
#define XACT_COMPLETION_FORCE_SYNC_COMMIT       (1U << 31)
 
/* Access macros for above flags */
#define XactCompletionApplyFeedback(xinfo) \
    ((xinfo & XACT_COMPLETION_APPLY_FEEDBACK) != 0)
#define XactCompletionRelcacheInitFileInval(xinfo) \
    ((xinfo & XACT_COMPLETION_UPDATE_RELCACHE_FILE) != 0)
#define XactCompletionForceSyncCommit(xinfo) \
    ((xinfo & XACT_COMPLETION_FORCE_SYNC_COMMIT) != 0)
 
typedef struct xl_xact_assignment
{
    TransactionId xtop;         /* assigned XID's top-level XID */
    int         nsubxacts;      /* number of subtransaction XIDs */
    TransactionId xsub[FLEXIBLE_ARRAY_MEMBER];  /* assigned subxids */
} xl_xact_assignment;
 
#define MinSizeOfXactAssignment offsetof(xl_xact_assignment, xsub)
 
/*
 * Commit and abort records can contain a lot of information. But a large
 * portion of the records won't need all possible pieces of information. So we
 * only include what's needed.
 *
 * A minimal commit/abort record only consists of a xl_xact_commit/abort
 * struct. The presence of additional information is indicated by bits set in
 * 'xl_xact_xinfo->xinfo'. The presence of the xinfo field itself is signaled
 * by a set XLOG_XACT_HAS_INFO bit in the xl_info field.
 *
 * NB: All the individual data chunks should be sized to multiples of
 * sizeof(int) and only require int32 alignment. If they require bigger
 * alignment, they need to be copied upon reading.
 */
 
/* sub-records for commit/abort */
 
typedef struct xl_xact_xinfo
{
    /*
     * Even though we right now only require two bytes of space in xinfo we
     * use four so following records don't have to care about alignment.
     * Commit records can be large, so copying large portions isn't
     * attractive.
     */
    uint32      xinfo;
} xl_xact_xinfo;
 
typedef struct xl_xact_dbinfo
{
    Oid         dbId;           /* MyDatabaseId */
    Oid         tsId;           /* MyDatabaseTableSpace */
} xl_xact_dbinfo;
 
typedef struct xl_xact_subxacts
{
    int         nsubxacts;      /* number of subtransaction XIDs */
    TransactionId subxacts[FLEXIBLE_ARRAY_MEMBER];
} xl_xact_subxacts;
#define MinSizeOfXactSubxacts offsetof(xl_xact_subxacts, subxacts)
 
typedef struct xl_xact_relfilelocators
{
    int         nrels;          /* number of relations */
    RelFileLocator xlocators[FLEXIBLE_ARRAY_MEMBER];
} xl_xact_relfilelocators;
#define MinSizeOfXactRelfileLocators offsetof(xl_xact_relfilelocators, xlocators)
 
/*
 * A transactionally dropped statistics entry.
 *
 * Declared here rather than pgstat.h because pgstat.h can't be included from
 * frontend code, but the WAL format needs to be readable by frontend
 * programs.
 */
typedef struct xl_xact_stats_item
{
    int         kind;
    Oid         dboid;
 
    /*
     * This stores the value of PgStat_HashKey.objid as two uint32 as all the
     * fields of xl_xact_xinfo should be multiples of size(int).
     */
    uint32      objid_lo;
    uint32      objid_hi;
} xl_xact_stats_item;
 
typedef struct xl_xact_stats_items
{
    int         nitems;
    xl_xact_stats_item items[FLEXIBLE_ARRAY_MEMBER];
} xl_xact_stats_items;
#define MinSizeOfXactStatsItems offsetof(xl_xact_stats_items, items)
 
typedef struct xl_xact_invals
{
    int         nmsgs;          /* number of shared inval msgs */
    SharedInvalidationMessage msgs[FLEXIBLE_ARRAY_MEMBER];
} xl_xact_invals;
#define MinSizeOfXactInvals offsetof(xl_xact_invals, msgs)
 
typedef struct xl_xact_twophase
{
    TransactionId xid;
} xl_xact_twophase;
 
typedef struct xl_xact_origin
{
    XLogRecPtr  origin_lsn;
    TimestampTz origin_timestamp;
} xl_xact_origin;
 
typedef struct xl_xact_commit
{
    TimestampTz xact_time;      /* time of commit */
 
    /* xl_xact_xinfo follows if XLOG_XACT_HAS_INFO */
    /* xl_xact_dbinfo follows if XINFO_HAS_DBINFO */
    /* xl_xact_subxacts follows if XINFO_HAS_SUBXACT */
    /* xl_xact_relfilelocators follows if XINFO_HAS_RELFILELOCATORS */
    /* xl_xact_stats_items follows if XINFO_HAS_DROPPED_STATS */
    /* xl_xact_invals follows if XINFO_HAS_INVALS */
    /* xl_xact_twophase follows if XINFO_HAS_TWOPHASE */
    /* twophase_gid follows if XINFO_HAS_GID. As a null-terminated string. */
    /* xl_xact_origin follows if XINFO_HAS_ORIGIN, stored unaligned! */
} xl_xact_commit;
#define MinSizeOfXactCommit (offsetof(xl_xact_commit, xact_time) + sizeof(TimestampTz))
 
typedef struct xl_xact_abort
{
    TimestampTz xact_time;      /* time of abort */
 
    /* xl_xact_xinfo follows if XLOG_XACT_HAS_INFO */
    /* xl_xact_dbinfo follows if XINFO_HAS_DBINFO */
    /* xl_xact_subxacts follows if XINFO_HAS_SUBXACT */
    /* xl_xact_relfilelocators follows if XINFO_HAS_RELFILELOCATORS */
    /* xl_xact_stats_items follows if XINFO_HAS_DROPPED_STATS */
    /* No invalidation messages needed. */
    /* xl_xact_twophase follows if XINFO_HAS_TWOPHASE */
    /* twophase_gid follows if XINFO_HAS_GID. As a null-terminated string. */
    /* xl_xact_origin follows if XINFO_HAS_ORIGIN, stored unaligned! */
} xl_xact_abort;
#define MinSizeOfXactAbort sizeof(xl_xact_abort)
 
typedef struct xl_xact_prepare
{
    uint32      magic;          /* format identifier */
    uint32      total_len;      /* actual file length */
    TransactionId xid;          /* original transaction XID */
    Oid         database;       /* OID of database it was in */
    TimestampTz prepared_at;    /* time of preparation */
    Oid         owner;          /* user running the transaction */
    int32       nsubxacts;      /* number of following subxact XIDs */
    int32       ncommitrels;    /* number of delete-on-commit rels */
    int32       nabortrels;     /* number of delete-on-abort rels */
    int32       ncommitstats;   /* number of stats to drop on commit */
    int32       nabortstats;    /* number of stats to drop on abort */
    int32       ninvalmsgs;     /* number of cache invalidation messages */
    bool        initfileinval;  /* does relcache init file need invalidation? */
    uint16      gidlen;         /* length of the GID - GID follows the header */
    XLogRecPtr  origin_lsn;     /* lsn of this record at origin node */
    TimestampTz origin_timestamp;   /* time of prepare at origin node */
} xl_xact_prepare;
 
/*
 * Commit/Abort records in the above form are a bit verbose to parse, so
 * there's a deconstructed versions generated by ParseCommit/AbortRecord() for
 * easier consumption.
 */
typedef struct xl_xact_parsed_commit
{
    TimestampTz xact_time;
    uint32      xinfo;
 
    Oid         dbId;           /* MyDatabaseId */
    Oid         tsId;           /* MyDatabaseTableSpace */
 
    int         nsubxacts;
    TransactionId *subxacts;
 
    int         nrels;
    RelFileLocator *xlocators;
 
    int         nstats;
    xl_xact_stats_item *stats;
 
    int         nmsgs;
    SharedInvalidationMessage *msgs;
 
    TransactionId twophase_xid; /* only for 2PC */
    char        twophase_gid[GIDSIZE];  /* only for 2PC */
    int         nabortrels;     /* only for 2PC */
    RelFileLocator *abortlocators;  /* only for 2PC */
    int         nabortstats;    /* only for 2PC */
    xl_xact_stats_item *abortstats; /* only for 2PC */
 
    XLogRecPtr  origin_lsn;
    TimestampTz origin_timestamp;
} xl_xact_parsed_commit;
 
typedef xl_xact_parsed_commit xl_xact_parsed_prepare;
 
typedef struct xl_xact_parsed_abort
{
    TimestampTz xact_time;
    uint32      xinfo;
 
    Oid         dbId;           /* MyDatabaseId */
    Oid         tsId;           /* MyDatabaseTableSpace */
 
    int         nsubxacts;
    TransactionId *subxacts;
 
    int         nrels;
    RelFileLocator *xlocators;
 
    int         nstats;
    xl_xact_stats_item *stats;
 
    TransactionId twophase_xid; /* only for 2PC */
    char        twophase_gid[GIDSIZE];  /* only for 2PC */
 
    XLogRecPtr  origin_lsn;
    TimestampTz origin_timestamp;
} xl_xact_parsed_abort;
 
 
/* ----------------
 *      extern definitions
 * ----------------
 */
extern bool IsTransactionState(void);
extern bool IsAbortedTransactionBlockState(void);
extern TransactionId GetTopTransactionId(void);
extern TransactionId GetTopTransactionIdIfAny(void);
extern TransactionId GetCurrentTransactionId(void);
extern TransactionId GetCurrentTransactionIdIfAny(void);
extern TransactionId GetStableLatestTransactionId(void);
extern SubTransactionId GetCurrentSubTransactionId(void);
extern FullTransactionId GetTopFullTransactionId(void);
extern FullTransactionId GetTopFullTransactionIdIfAny(void);
extern FullTransactionId GetCurrentFullTransactionId(void);
extern FullTransactionId GetCurrentFullTransactionIdIfAny(void);
extern void MarkCurrentTransactionIdLoggedIfAny(void);
extern bool SubTransactionIsActive(SubTransactionId subxid);
extern CommandId GetCurrentCommandId(bool used);
extern void SetParallelStartTimestamps(TimestampTz xact_ts, TimestampTz stmt_ts);
extern TimestampTz GetCurrentTransactionStartTimestamp(void);
extern TimestampTz GetCurrentStatementStartTimestamp(void);
extern TimestampTz GetCurrentTransactionStopTimestamp(void);
extern void SetCurrentStatementStartTimestamp(void);
extern int  GetCurrentTransactionNestLevel(void);
extern bool TransactionIdIsCurrentTransactionId(TransactionId xid);
extern void CommandCounterIncrement(void);
extern void ForceSyncCommit(void);
extern void StartTransactionCommand(void);
extern void SaveTransactionCharacteristics(SavedTransactionCharacteristics *s);
extern void RestoreTransactionCharacteristics(const SavedTransactionCharacteristics *s);
extern void CommitTransactionCommand(void);
extern void AbortCurrentTransaction(void);
extern void BeginTransactionBlock(void);
extern bool EndTransactionBlock(bool chain);
extern bool PrepareTransactionBlock(const char *gid);
extern void UserAbortTransactionBlock(bool chain);
extern void BeginImplicitTransactionBlock(void);
extern void EndImplicitTransactionBlock(void);
extern void ReleaseSavepoint(const char *name);
extern void DefineSavepoint(const char *name);
extern void RollbackToSavepoint(const char *name);
extern void BeginInternalSubTransaction(const char *name);
extern void ReleaseCurrentSubTransaction(void);
extern void RollbackAndReleaseCurrentSubTransaction(void);
extern bool IsSubTransaction(void);
extern Size EstimateTransactionStateSpace(void);
extern void SerializeTransactionState(Size maxsize, char *start_address);
extern void StartParallelWorkerTransaction(char *tstatespace);
extern void EndParallelWorkerTransaction(void);
extern bool IsTransactionBlock(void);
extern bool IsTransactionOrTransactionBlock(void);
extern char TransactionBlockStatusCode(void);
extern void AbortOutOfAnyTransaction(void);
extern void PreventInTransactionBlock(bool isTopLevel, const char *stmtType);
extern void RequireTransactionBlock(bool isTopLevel, const char *stmtType);
extern void WarnNoTransactionBlock(bool isTopLevel, const char *stmtType);
extern bool IsInTransactionBlock(bool isTopLevel);
extern void RegisterXactCallback(XactCallback callback, void *arg);
extern void UnregisterXactCallback(XactCallback callback, void *arg);
extern void RegisterSubXactCallback(SubXactCallback callback, void *arg);
extern void UnregisterSubXactCallback(SubXactCallback callback, void *arg);
 
extern bool IsSubxactTopXidLogPending(void);
extern void MarkSubxactTopXidLogged(void);
 
extern int  xactGetCommittedChildren(TransactionId **ptr);
 
extern XLogRecPtr XactLogCommitRecord(TimestampTz commit_time,
                                      int nsubxacts, TransactionId *subxacts,
                                      int nrels, RelFileLocator *rels,
                                      int ndroppedstats,
                                      xl_xact_stats_item *droppedstats,
                                      int nmsgs, SharedInvalidationMessage *msgs,
                                      bool relcacheInval,
                                      int xactflags,
                                      TransactionId twophase_xid,
                                      const char *twophase_gid);
 
extern XLogRecPtr XactLogAbortRecord(TimestampTz abort_time,
                                     int nsubxacts, TransactionId *subxacts,
                                     int nrels, RelFileLocator *rels,
                                     int ndroppedstats,
                                     xl_xact_stats_item *droppedstats,
                                     int xactflags, TransactionId twophase_xid,
                                     const char *twophase_gid);
extern void xact_redo(XLogReaderState *record);
 
/* xactdesc.c */
extern void xact_desc(StringInfo buf, XLogReaderState *record);
extern const char *xact_identify(uint8 info);
 
/* also in xactdesc.c, so they can be shared between front/backend code */
extern void ParseCommitRecord(uint8 info, xl_xact_commit *xlrec, xl_xact_parsed_commit *parsed);
extern void ParseAbortRecord(uint8 info, xl_xact_abort *xlrec, xl_xact_parsed_abort *parsed);
extern void ParsePrepareRecord(uint8 info, xl_xact_prepare *xlrec, xl_xact_parsed_prepare *parsed);
 
extern void EnterParallelMode(void);
extern void ExitParallelMode(void);
extern bool IsInParallelMode(void);
 
#endif                          /* XACT_H */