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/xlog.c | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'src/backend/access/transam/xlog.c') diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index 1b7c2f23a41..b540ee293b6 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -4469,6 +4469,17 @@ LocalProcessControlFile(bool reset) ReadControlFile(); } +/* + * Get the wal_level from the control file. For a standby, this value should be + * considered as its active wal_level, because it may be different from what + * was originally configured on standby. + */ +WalLevel +GetActiveWalLevelOnStandby(void) +{ + return ControlFile->wal_level; +} + /* * Initialization of shared memory for XLOG */ -- cgit v1.2.3