From 563431ffb53d0b598f33d3378b7ba40338020ca6 Mon Sep 17 00:00:00 2001 From: Mikhail Litsarev Date: Tue, 20 Feb 2024 20:05:37 +0300 Subject: [PATCH 1/2] Introduce pg_is_standby_requested(). Introduce pg_is_standby_requested() function to distinguish a replica from a regular instance in point in time recovery mode. --- src/backend/access/transam/xlogfuncs.c | 14 ++++++++++ src/backend/access/transam/xlogrecovery.c | 33 +++++++++++++++++++++++ src/include/access/xlogrecovery.h | 1 + src/include/catalog/pg_proc.dat | 4 +++ 4 files changed, 52 insertions(+) diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c index 45452d937c7..3170c4ef343 100644 --- a/src/backend/access/transam/xlogfuncs.c +++ b/src/backend/access/transam/xlogfuncs.c @@ -753,3 +753,17 @@ pg_promote(PG_FUNCTION_ARGS) wait_seconds))); PG_RETURN_BOOL(false); } + +/* + * Returns bool with a current value of StandbyModeIsRequested flag + * to distinguish a replica from a regular instance in a + * Point In Time Recovery (PITR) mode. + * + * Returns true if standby.signal file is found at startup process + * false otherwise + */ +Datum +pg_is_standby_requested(PG_FUNCTION_ARGS) +{ + PG_RETURN_BOOL(StandbyModeIsRequested()); +} diff --git a/src/backend/access/transam/xlogrecovery.c b/src/backend/access/transam/xlogrecovery.c index 6318878356a..cbca4c5055d 100644 --- a/src/backend/access/transam/xlogrecovery.c +++ b/src/backend/access/transam/xlogrecovery.c @@ -321,6 +321,12 @@ typedef struct XLogRecoveryCtlData */ bool SharedPromoteIsTriggered; + /* + * SharedStandbyModeRequested indicates if we're in a standby mode at + * start, while recovery mode is on. Protected by info_lck. + */ + bool SharedStandbyModeRequested; + /* * recoveryWakeupLatch is used to wake up the startup process to continue * WAL replay, if it is waiting for WAL to arrive or promotion to be @@ -1070,7 +1076,16 @@ readRecoverySignalFile(void) ArchiveRecoveryRequested = true; } else + { + /* + * There is no need to use Spinlock here because only the startup + * process modifies the SharedStandbyModeRequested variable here and + * no other processes are reading it at that time. + */ + XLogRecoveryCtl->SharedStandbyModeRequested = StandbyModeRequested; return; + } + XLogRecoveryCtl->SharedStandbyModeRequested = StandbyModeRequested; /* * We don't support standby mode in standalone backends; that requires @@ -4555,6 +4570,24 @@ HotStandbyActiveInReplay(void) return LocalHotStandbyActive; } + +/* + * It reports wether a standby.signal file is in the data directory + * at startup. + * + * This works in any process that's connected to shared memory. + */ +bool +StandbyModeIsRequested(void) +{ + /* + * Spinlock is not needed here because SharedStandbyModeRequested variable + * can only be read after startup process is done and no other actions (in + * functions, in processes) change it then. + */ + return XLogRecoveryCtl->SharedStandbyModeRequested; +} + /* * Get latest redo apply position. * diff --git a/src/include/access/xlogrecovery.h b/src/include/access/xlogrecovery.h index 66affd2eac3..f85a2af6a23 100644 --- a/src/include/access/xlogrecovery.h +++ b/src/include/access/xlogrecovery.h @@ -145,6 +145,7 @@ extern TimestampTz GetLatestXTime(void); extern TimestampTz GetCurrentChunkReplayStartTime(void); extern XLogRecPtr GetCurrentReplayRecPtr(TimeLineID *replayEndTLI); +extern bool StandbyModeIsRequested(void); extern bool PromoteIsTriggered(void); extern bool CheckPromoteSignal(void); extern void WakeupRecovery(void); diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat index bb775ce7264..a2ac4160d8c 100644 --- a/src/include/catalog/pg_proc.dat +++ b/src/include/catalog/pg_proc.dat @@ -6494,6 +6494,10 @@ { oid => '3810', descr => 'true if server is in recovery', proname => 'pg_is_in_recovery', provolatile => 'v', prorettype => 'bool', proargtypes => '', prosrc => 'pg_is_in_recovery' }, +{ oid => '8439', + descr => 'Is StandbyMode requested at startup while being in recovery mode', + proname => 'pg_is_standby_requested', provolatile => 'v', prorettype => 'bool', + proargtypes => '', prosrc => 'pg_is_standby_requested' }, { oid => '3820', descr => 'current wal flush location', proname => 'pg_last_wal_receive_lsn', provolatile => 'v', -- 2.34.1 From 3d944423ed1c0f2a73e4a38a61ac545f0450a70d Mon Sep 17 00:00:00 2001 From: Mikhail Litsarev Date: Tue, 27 Feb 2024 14:08:42 +0300 Subject: [PATCH 2/2] Test pg_is_standby_requested() in different use-cases. Add tiny tests in src/test/recovery/t/004_timeline_switch.pl They validate: - master is not a replica - standby_1 is a replica - promoted replica in master mode - standby_2 remains a replica after switch to promoted master --- src/test/recovery/t/004_timeline_switch.pl | 23 ++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/src/test/recovery/t/004_timeline_switch.pl b/src/test/recovery/t/004_timeline_switch.pl index edaef918454..e3f320ab9ab 100644 --- a/src/test/recovery/t/004_timeline_switch.pl +++ b/src/test/recovery/t/004_timeline_switch.pl @@ -18,6 +18,11 @@ my $node_primary = PostgreSQL::Test::Cluster->new('primary'); $node_primary->init(allows_streaming => 1); $node_primary->start; +# Validate pg_is_standby_requested() for master +my $ret_mode_primary = $node_primary->safe_psql('postgres', + 'SELECT pg_is_standby_requested()'); +is($ret_mode_primary, 'f', "master is not a replica"); + # Take backup my $backup_name = 'my_backup'; $node_primary->backup($backup_name); @@ -32,6 +37,11 @@ $node_standby_2->init_from_backup($node_primary, $backup_name, has_streaming => 1); $node_standby_2->start; +# Validate pg_is_standby_requested() for replica node +my $ret_mode_standby_1 = $node_standby_1->safe_psql('postgres', + 'SELECT pg_is_standby_requested()'); +is($ret_mode_standby_1, 't', "node_standby_1 is a replica"); + # Create some content on primary $node_primary->safe_psql('postgres', "CREATE TABLE tab_int AS SELECT generate_series(1,1000) AS a"); @@ -50,6 +60,14 @@ $node_standby_1->psql( stdout => \$psql_out); is($psql_out, 't', "promotion of standby with pg_promote"); +# Validate pg_is_standby_requested() for master promoted from standby node. +# pg_is_standby_requested() returns true because standby.signal file +# was found while being a replica. +# Use it with pg_is_in_recovery() (returns false), for such use-cases. +my $ret_mode_1 = $node_standby_1->safe_psql('postgres', + 'SELECT pg_is_standby_requested()'); +is($ret_mode_1, 't', "node_standby_1 becomes a master"); + # Switch standby 2 to replay from standby 1 my $connstr_1 = $node_standby_1->connstr; $node_standby_2->append_conf( @@ -58,6 +76,11 @@ primary_conninfo='$connstr_1' )); $node_standby_2->restart; +# Validate pg_is_standby_requested() for second replica after restart +my $ret_mode_standby_2 = $node_standby_2->safe_psql('postgres', + 'SELECT pg_is_standby_requested()'); +is($ret_mode_standby_2, 't', "node_standby_2 remains a replica"); + # Insert some data in standby 1 and check its presence in standby 2 # to ensure that the timeline switch has been done. $node_standby_1->safe_psql('postgres', -- 2.34.1