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Allow logical decoding on standbys

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Unsurprisingly, this requires wal_level = logical to be set on the primary and
standby. The infrastructure added in 26669757b6a ensures that slots are
invalidated if the primary's wal_level is lowered.

Creating a slot on a standby waits for a xl_running_xact record to be
processed. If the primary is idle (and thus not emitting xl_running_xact
records), that can take a while.  To make that faster, this commit also
introduces the pg_log_standby_snapshot() function. By executing it on the
primary, completion of slot creation on the standby can be accelerated.

Note that logical decoding on a standby does not itself enforce that required
catalog rows are not removed. The user has to use physical replication slots +
hot_standby_feedback or other measures to prevent that. If catalog rows
required for a slot are removed, the slot is invalidated.

See 6af1793954e for an overall design of logical decoding on a standby.

Bumps catversion, for the addition of the pg_log_standby_snapshot() function.

Author: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Author: Andres Freund <andres@anarazel.de> (in an older version)
Author: Amit Khandekar <amitdkhan.pg@gmail.com> (in an older version)
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: FabrÌzio de Royes Mello <fabriziomello@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-By: Robert Haas <robertmhaas@gmail.com>
This commit is contained in:
Andres Freund
2023-04-08 02:20:01 -07:00
parent e101dfac3a
commit 0fdab27ad6
12 changed files with 203 additions and 62 deletions
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1
src/include/access/xlog.h
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@ -230,6 +230,7 @@ extern void XLOGShmemInit(void);
extern void BootStrapXLOG(void);
extern void InitializeWalConsistencyChecking(void);
extern void LocalProcessControlFile(bool reset);
extern WalLevel GetActiveWalLevelOnStandby(void);
extern void StartupXLOG(void);
extern void ShutdownXLOG(int code, Datum arg);
extern void CreateCheckPoint(int flags);

2
src/include/catalog/catversion.h
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@ -57,6 +57,6 @@
*/
/* yyyymmddN */
#define CATALOG_VERSION_NO 202304074
#define CATALOG_VERSION_NO 202304075
#endif

3
src/include/catalog/pg_proc.dat
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@ -6432,6 +6432,9 @@
{ oid => '2848', descr => 'switch to new wal file',
proname => 'pg_switch_wal', provolatile => 'v', prorettype => 'pg_lsn',
proargtypes => '', prosrc => 'pg_switch_wal' },
{ oid => '9658', descr => 'log details of the current snapshot to WAL',
proname => 'pg_log_standby_snapshot', provolatile => 'v', prorettype => 'pg_lsn',
proargtypes => '', prosrc => 'pg_log_standby_snapshot' },
{ oid => '3098', descr => 'create a named restore point',
proname => 'pg_create_restore_point', provolatile => 'v',
prorettype => 'pg_lsn', proargtypes => 'text',