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Fix replay of create database records on standby
Crash recovery on standby may encounter missing directories when replaying database-creation WAL records. Prior to this patch, the standby would fail to recover in such a case; however, the directories could be legitimately missing. Consider the following sequence of commands: CREATE DATABASE DROP DATABASE DROP TABLESPACE If, after replaying the last WAL record and removing the tablespace directory, the standby crashes and has to replay the create database record again, crash recovery must be able to continue. A fix for this problem was already attempted in 49d9cfc, but it was reverted because of design issues. This new version is based on Robert Haas' proposal: any missing tablespaces are created during recovery before reaching consistency. Tablespaces are created as real directories, and should be deleted by later replay. CheckRecoveryConsistency ensures they have disappeared. The problems detected by this new code are reported as PANIC, except when allow_in_place_tablespaces is set to ON, in which case they are WARNING. Apart from making tests possible, this gives users an escape hatch in case things don't go as planned. Author: Kyotaro Horiguchi <[email protected]> Author: Asim R Praveen <[email protected]> Author: Paul Guo <[email protected]> Reviewed-by: Anastasia Lubennikova <[email protected]> (older versions) Reviewed-by: Fujii Masao <[email protected]> (older versions) Reviewed-by: Michaël Paquier <[email protected]> Diagnosed-by: Paul Guo <[email protected]> Discussion: https://postgr.es/m/CAEET0ZGx9AvioViLf7nbR_8tH9-=27DN5xWJ2P9-ROH16e4JUA@mail.gmail.com
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4 files changed

+301
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lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 61 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -7991,6 +7991,59 @@ StartupXLOG(void)
79917991
RequestCheckpoint(CHECKPOINT_FORCE);
79927992
}
79937993

7994+
/*
7995+
* Verify that, in non-test mode, ./pg_tblspc doesn't contain any real
7996+
* directories.
7997+
*
7998+
* Replay of database creation XLOG records for databases that were later
7999+
* dropped can create fake directories in pg_tblspc. By the time consistency
8000+
* is reached these directories should have been removed; here we verify
8001+
* that this did indeed happen. This is to be called at the point where
8002+
* consistent state is reached.
8003+
*
8004+
* allow_in_place_tablespaces turns the PANIC into a WARNING, which is
8005+
* useful for testing purposes, and also allows for an escape hatch in case
8006+
* things go south.
8007+
*/
8008+
static void
8009+
CheckTablespaceDirectory(void)
8010+
{
8011+
DIR *dir;
8012+
struct dirent *de;
8013+
8014+
dir = AllocateDir("pg_tblspc");
8015+
while ((de = ReadDir(dir, "pg_tblspc")) != NULL)
8016+
{
8017+
char path[MAXPGPATH + 10];
8018+
#ifndef WIN32
8019+
struct stat st;
8020+
#endif
8021+
8022+
/* Skip entries of non-oid names */
8023+
if (strspn(de->d_name, "0123456789") != strlen(de->d_name))
8024+
continue;
8025+
8026+
snprintf(path, sizeof(path), "pg_tblspc/%s", de->d_name);
8027+
8028+
#ifndef WIN32
8029+
if (lstat(path, &st) < 0)
8030+
ereport(LOG,
8031+
(errcode_for_file_access(),
8032+
errmsg("could not stat file \"%s\": %m",
8033+
path)));
8034+
else if (!S_ISLNK(st.st_mode))
8035+
#else /* WIN32 */
8036+
if (!pgwin32_is_junction(path))
8037+
#endif
8038+
ereport(allow_in_place_tablespaces ? WARNING : PANIC,
8039+
(errcode(ERRCODE_DATA_CORRUPTED),
8040+
errmsg("unexpected directory entry \"%s\" found in %s",
8041+
de->d_name, "pg_tblspc/"),
8042+
errdetail("All directory entries in pg_tblspc/ should be symbolic links."),
8043+
errhint("Remove those directories, or set allow_in_place_tablespaces to ON transiently to let recovery complete.")));
8044+
}
8045+
}
8046+
79948047
/*
79958048
* Checks if recovery has reached a consistent state. When consistency is
79968049
* reached and we have a valid starting standby snapshot, tell postmaster
@@ -8061,6 +8114,14 @@ CheckRecoveryConsistency(void)
80618114
*/
80628115
XLogCheckInvalidPages();
80638116

8117+
/*
8118+
* Check that pg_tblspc doesn't contain any real directories. Replay
8119+
* of Database/CREATE_* records may have created ficticious tablespace
8120+
* directories that should have been removed by the time consistency
8121+
* was reached.
8122+
*/
8123+
CheckTablespaceDirectory();
8124+
80648125
reachedConsistency = true;
80658126
ereport(LOG,
80668127
(errmsg("consistent recovery state reached at %X/%X",

‎src/backend/commands/dbcommands.c

Lines changed: 68 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2070,6 +2070,45 @@ get_database_name(Oid dbid)
20702070
return result;
20712071
}
20722072

2073+
/*
2074+
* recovery_create_dbdir()
2075+
*
2076+
* During recovery, there's a case where we validly need to recover a missing
2077+
* tablespace directory so that recovery can continue. This happens when
2078+
* recovery wants to create a database but the holding tablespace has been
2079+
* removed before the server stopped. Since we expect that the directory will
2080+
* be gone before reaching recovery consistency, and we have no knowledge about
2081+
* the tablespace other than its OID here, we create a real directory under
2082+
* pg_tblspc here instead of restoring the symlink.
2083+
*
2084+
* If only_tblspc is true, then the requested directory must be in pg_tblspc/
2085+
*/
2086+
static void
2087+
recovery_create_dbdir(char *path, bool only_tblspc)
2088+
{
2089+
struct stat st;
2090+
2091+
Assert(RecoveryInProgress());
2092+
2093+
if (stat(path, &st) == 0)
2094+
return;
2095+
2096+
if (only_tblspc && strstr(path, "pg_tblspc/") == NULL)
2097+
elog(PANIC, "requested to created invalid directory: %s", path);
2098+
2099+
if (reachedConsistency && !allow_in_place_tablespaces)
2100+
ereport(PANIC,
2101+
(errmsg("missing directory \"%s\"", path)));
2102+
2103+
elog(reachedConsistency ? WARNING : DEBUG1,
2104+
"creating missing directory: %s", path);
2105+
2106+
if (pg_mkdir_p(path, S_IRWXU) != 0)
2107+
ereport(PANIC,
2108+
(errmsg("could not create missing directory \"%s\": %m", path)));
2109+
}
2110+
2111+
20732112
/*
20742113
* DATABASE resource manager's routines
20752114
*/
@@ -2086,6 +2125,7 @@ dbase_redo(XLogReaderState *record)
20862125
xl_dbase_create_rec *xlrec = (xl_dbase_create_rec *) XLogRecGetData(record);
20872126
char *src_path;
20882127
char *dst_path;
2128+
char *parent_path;
20892129
struct stat st;
20902130

20912131
src_path = GetDatabasePath(xlrec->src_db_id, xlrec->src_tablespace_id);
@@ -2105,6 +2145,34 @@ dbase_redo(XLogReaderState *record)
21052145
dst_path)));
21062146
}
21072147

2148+
/*
2149+
* If the parent of the target path doesn't exist, create it now. This
2150+
* enables us to create the target underneath later. Note that if
2151+
* the database dir is not in a tablespace, the parent will always
2152+
* exist, so this never runs in that case.
2153+
*/
2154+
parent_path = pstrdup(dst_path);
2155+
get_parent_directory(parent_path);
2156+
if (stat(parent_path, &st) < 0)
2157+
{
2158+
if (errno != ENOENT)
2159+
ereport(FATAL,
2160+
(errmsg("could not stat directory \"%s\": %m",
2161+
dst_path)));
2162+
2163+
recovery_create_dbdir(parent_path, true);
2164+
}
2165+
pfree(parent_path);
2166+
2167+
/*
2168+
* There's a case where the copy source directory is missing for the
2169+
* same reason above. Create the emtpy source directory so that
2170+
* copydir below doesn't fail. The directory will be dropped soon by
2171+
* recovery.
2172+
*/
2173+
if (stat(src_path, &st) < 0 && errno == ENOENT)
2174+
recovery_create_dbdir(src_path, false);
2175+
21082176
/*
21092177
* Force dirty buffers out to disk, to ensure source database is
21102178
* up-to-date for the copy.

‎src/backend/commands/tablespace.c

Lines changed: 9 additions & 31 deletions
Original file line numberDiff line numberDiff line change
@@ -154,8 +154,6 @@ TablespaceCreateDbspace(Oid spcNode, Oid dbNode, bool isRedo)
154154
/* Directory creation failed? */
155155
if (mkdir(dir, S_IRWXU) < 0)
156156
{
157-
char *parentdir;
158-
159157
/* Failure other than not exists or not in WAL replay? */
160158
if (errno != ENOENT || !isRedo)
161159
ereport(ERROR,
@@ -164,36 +162,16 @@ TablespaceCreateDbspace(Oid spcNode, Oid dbNode, bool isRedo)
164162
dir)));
165163

166164
/*
167-
* Parent directories are missing during WAL replay, so
168-
* continue by creating simple parent directories rather
169-
* than a symlink.
165+
* During WAL replay, it's conceivable that several levels
166+
* of directories are missing if tablespaces are dropped
167+
* further ahead of the WAL stream than we're currently
168+
* replaying. An easy way forward is to create them as
169+
* plain directories and hope they are removed by further
170+
* WAL replay if necessary. If this also fails, there is
171+
* trouble we cannot get out of, so just report that and
172+
* bail out.
170173
*/
171-
172-
/* create two parents up if not exist */
173-
parentdir = pstrdup(dir);
174-
get_parent_directory(parentdir);
175-
get_parent_directory(parentdir);
176-
/* Can't create parent and it doesn't already exist? */
177-
if (mkdir(parentdir, S_IRWXU) < 0 && errno != EEXIST)
178-
ereport(ERROR,
179-
(errcode_for_file_access(),
180-
errmsg("could not create directory \"%s\": %m",
181-
parentdir)));
182-
pfree(parentdir);
183-
184-
/* create one parent up if not exist */
185-
parentdir = pstrdup(dir);
186-
get_parent_directory(parentdir);
187-
/* Can't create parent and it doesn't already exist? */
188-
if (mkdir(parentdir, S_IRWXU) < 0 && errno != EEXIST)
189-
ereport(ERROR,
190-
(errcode_for_file_access(),
191-
errmsg("could not create directory \"%s\": %m",
192-
parentdir)));
193-
pfree(parentdir);
194-
195-
/* Create database directory */
196-
if (mkdir(dir, S_IRWXU) < 0)
174+
if (pg_mkdir_p(dir, S_IRWXU) < 0)
197175
ereport(ERROR,
198176
(errcode_for_file_access(),
199177
errmsg("could not create directory \"%s\": %m",

‎src/test/recovery/t/033_replay_tsp_drops.pl

Lines changed: 163 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,163 @@
1+
2+
# Copyright (c) 2021-2022, PostgreSQL Global Development Group
3+
4+
# Test replay of tablespace/database creation/drop
5+
6+
use strict;
7+
use warnings;
8+
9+
use PostgreSQL::Test::Cluster;
10+
use PostgreSQL::Test::Utils;
11+
use Test::More;
12+
13+
sub test_tablespace
14+
{
15+
my $node_primary = PostgreSQL::Test::Cluster->new("primary1");
16+
$node_primary->init(allows_streaming => 1);
17+
$node_primary->start;
18+
$node_primary->psql(
19+
'postgres',
20+
qq[
21+
SET allow_in_place_tablespaces=on;
22+
CREATE TABLESPACE dropme_ts1 LOCATION '';
23+
CREATE TABLESPACE dropme_ts2 LOCATION '';
24+
CREATE TABLESPACE source_ts LOCATION '';
25+
CREATE TABLESPACE target_ts LOCATION '';
26+
CREATE DATABASE template_db IS_TEMPLATE = true;
27+
]);
28+
my $backup_name = 'my_backup';
29+
$node_primary->backup($backup_name);
30+
31+
my $node_standby = PostgreSQL::Test::Cluster->new("standby2");
32+
$node_standby->init_from_backup($node_primary, $backup_name,
33+
has_streaming => 1);
34+
$node_standby->append_conf('postgresql.conf',
35+
"allow_in_place_tablespaces = on");
36+
$node_standby->start;
37+
38+
# Make sure connection is made
39+
$node_primary->poll_query_until('postgres',
40+
'SELECT count(*) = 1 FROM pg_stat_replication');
41+
42+
$node_standby->safe_psql('postgres', 'CHECKPOINT');
43+
44+
# Do immediate shutdown just after a sequence of CREAT DATABASE / DROP
45+
# DATABASE / DROP TABLESPACE. This causes CREATE DATABASE WAL records
46+
# to be applied to already-removed directories.
47+
my $query = q[
48+
CREATE DATABASE dropme_db1 WITH TABLESPACE dropme_ts1;
49+
CREATE TABLE t (a int) TABLESPACE dropme_ts2;
50+
CREATE DATABASE dropme_db2 WITH TABLESPACE dropme_ts2;
51+
CREATE DATABASE moveme_db TABLESPACE source_ts;
52+
ALTER DATABASE moveme_db SET TABLESPACE target_ts;
53+
CREATE DATABASE newdb TEMPLATE template_db;
54+
ALTER DATABASE template_db IS_TEMPLATE = false;
55+
DROP DATABASE dropme_db1;
56+
DROP TABLE t;
57+
DROP DATABASE dropme_db2; DROP TABLESPACE dropme_ts2;
58+
DROP TABLESPACE source_ts;
59+
DROP DATABASE template_db;
60+
];
61+
62+
$node_primary->safe_psql('postgres', $query);
63+
$node_primary->wait_for_catchup($node_standby, 'replay',
64+
$node_primary->lsn('write'));
65+
66+
# show "create missing directory" log message
67+
$node_standby->safe_psql('postgres',
68+
"ALTER SYSTEM SET log_min_messages TO debug1;");
69+
$node_standby->stop('immediate');
70+
# Should restart ignoring directory creation error.
71+
is($node_standby->start(fail_ok => 1), 1, "standby node started");
72+
$node_standby->stop('immediate');
73+
}
74+
75+
test_tablespace();
76+
77+
# Ensure that a missing tablespace directory during create database
78+
# replay immediately causes panic if the standby has already reached
79+
# consistent state (archive recovery is in progress).
80+
81+
my $node_primary = PostgreSQL::Test::Cluster->new('primary2');
82+
$node_primary->init(allows_streaming => 1);
83+
$node_primary->start;
84+
85+
# Create tablespace
86+
$node_primary->safe_psql(
87+
'postgres', q[
88+
SET allow_in_place_tablespaces=on;
89+
CREATE TABLESPACE ts1 LOCATION ''
90+
]);
91+
$node_primary->safe_psql('postgres',
92+
"CREATE DATABASE db1 WITH TABLESPACE ts1");
93+
94+
# Take backup
95+
my $backup_name = 'my_backup';
96+
$node_primary->backup($backup_name);
97+
my $node_standby = PostgreSQL::Test::Cluster->new('standby3');
98+
$node_standby->init_from_backup($node_primary, $backup_name,
99+
has_streaming => 1);
100+
$node_standby->append_conf('postgresql.conf',
101+
"allow_in_place_tablespaces = on");
102+
$node_standby->start;
103+
104+
# Make sure standby reached consistency and starts accepting connections
105+
$node_standby->poll_query_until('postgres', 'SELECT 1', '1');
106+
107+
# Remove standby tablespace directory so it will be missing when
108+
# replay resumes.
109+
my $tspoid = $node_standby->safe_psql('postgres',
110+
"SELECT oid FROM pg_tablespace WHERE spcname = 'ts1';");
111+
my $tspdir = $node_standby->data_dir . "/pg_tblspc/$tspoid";
112+
File::Path::rmtree($tspdir);
113+
114+
my $logstart = get_log_size($node_standby);
115+
116+
# Create a database in the tablespace and a table in default tablespace
117+
$node_primary->safe_psql(
118+
'postgres',
119+
q[
120+
CREATE TABLE should_not_replay_insertion(a int);
121+
CREATE DATABASE db2 WITH TABLESPACE ts1;
122+
INSERT INTO should_not_replay_insertion VALUES (1);
123+
]);
124+
125+
# Standby should fail and should not silently skip replaying the wal
126+
# In this test, PANIC turns into WARNING by allow_in_place_tablespaces.
127+
# Check the log messages instead of confirming standby failure.
128+
my $max_attempts = $PostgreSQL::Test::Utils::timeout_default;
129+
while ($max_attempts-- >= 0)
130+
{
131+
last
132+
if (
133+
find_in_log(
134+
$node_standby, "WARNING: creating missing directory: pg_tblspc/",
135+
$logstart));
136+
sleep 1;
137+
}
138+
ok($max_attempts > 0, "invalid directory creation is detected");
139+
140+
done_testing();
141+
142+
143+
# return the size of logfile of $node in bytes
144+
sub get_log_size
145+
{
146+
my ($node) = @_;
147+
148+
return (stat $node->logfile)[7];
149+
}
150+
151+
# find $pat in logfile of $node after $off-th byte
152+
sub find_in_log
153+
{
154+
my ($node, $pat, $off) = @_;
155+
156+
$off = 0 unless defined $off;
157+
my $log = PostgreSQL::Test::Utils::slurp_file($node->logfile);
158+
return 0 if (length($log) <= $off);
159+
160+
$log = substr($log, $off);
161+
162+
return $log =~ m/$pat/;
163+
}

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