From 0fdab27ad68a059a1663fa5ce48d76333f1bd74c Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Sat, 8 Apr 2023 02:20:01 -0700 Subject: Allow logical decoding on standbys MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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" Author: Andres Freund (in an older version) Author: Amit Khandekar (in an older version) Reviewed-by: Andres Freund Reviewed-by: FabrÌzio de Royes Mello Reviewed-by: Amit Kapila Reviewed-By: Robert Haas --- src/backend/access/transam/xlogfuncs.c | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) (limited to 'src/backend/access/transam/xlogfuncs.c') diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c index c07daa874f9..52f827a902d 100644 --- a/src/backend/access/transam/xlogfuncs.c +++ b/src/backend/access/transam/xlogfuncs.c @@ -31,6 +31,7 @@ #include "storage/fd.h" #include "storage/ipc.h" #include "storage/smgr.h" +#include "storage/standby.h" #include "utils/builtins.h" #include "utils/guc.h" #include "utils/memutils.h" @@ -196,6 +197,36 @@ pg_switch_wal(PG_FUNCTION_ARGS) PG_RETURN_LSN(switchpoint); } +/* + * pg_log_standby_snapshot: call LogStandbySnapshot() + * + * Permission checking for this function is managed through the normal + * GRANT system. + */ +Datum +pg_log_standby_snapshot(PG_FUNCTION_ARGS) +{ + XLogRecPtr recptr; + + if (RecoveryInProgress()) + ereport(ERROR, + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), + errmsg("recovery is in progress"), + errhint("pg_log_standby_snapshot() cannot be executed during recovery."))); + + if (!XLogStandbyInfoActive()) + ereport(ERROR, + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), + errmsg("pg_log_standby_snapshot() can only be used if wal_level >= replica"))); + + recptr = LogStandbySnapshot(); + + /* + * As a convenience, return the WAL location of the last inserted record + */ + PG_RETURN_LSN(recptr); +} + /* * pg_create_restore_point: a named point for restore * -- cgit v1.2.3