From 99c8350040a14b38eeebf3e44d2b190fe1c44889 Mon Sep 17 00:00:00 2001 From: Shlok Kyal Date: Mon, 8 Sep 2025 21:04:42 +0530 Subject: [PATCH v4 1/2] Add stats related to slot sync skip When slot sync is performed, it can happen that it is skipped due to various reason. This patch adds stats for synced slots regarding this slot sync skip. This patch adds new columns slot_sync_skip_count, last_slot_sync_skip to view pg_stat_replication_slots and new column slot_sync_skip_reason to view pg_replication_slots. --- contrib/test_decoding/expected/stats.out | 12 ++-- doc/src/sgml/monitoring.sgml | 20 +++++++ doc/src/sgml/system-views.sgml | 8 +++ src/backend/catalog/system_views.sql | 5 +- src/backend/replication/logical/slotsync.c | 59 +++++++++++++++++++- src/backend/replication/slotfuncs.c | 26 ++++++++- src/backend/utils/activity/pgstat_replslot.c | 25 +++++++++ src/backend/utils/adt/pgstatfuncs.c | 18 ++++-- src/include/catalog/pg_proc.dat | 12 ++-- src/include/pgstat.h | 3 + src/include/replication/slot.h | 18 ++++++ src/test/regress/expected/rules.out | 9 ++- src/tools/pgindent/typedefs.list | 1 + 13 files changed, 193 insertions(+), 23 deletions(-) diff --git a/contrib/test_decoding/expected/stats.out b/contrib/test_decoding/expected/stats.out index de6dc416130..c1ff872c08c 100644 --- a/contrib/test_decoding/expected/stats.out +++ b/contrib/test_decoding/expected/stats.out @@ -78,17 +78,17 @@ SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, -- verify accessing/resetting stats for non-existent slot does something reasonable SELECT * FROM pg_stat_get_replication_slot('do-not-exist'); - slot_name | spill_txns | spill_count | spill_bytes | stream_txns | stream_count | stream_bytes | total_txns | total_bytes | stats_reset ---------------+------------+-------------+-------------+-------------+--------------+--------------+------------+-------------+------------- - do-not-exist | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | + slot_name | spill_txns | spill_count | spill_bytes | stream_txns | stream_count | stream_bytes | total_txns | total_bytes | slot_sync_skip_count | last_slot_sync_skip | stats_reset +--------------+------------+-------------+-------------+-------------+--------------+--------------+------------+-------------+----------------------+---------------------+------------- + do-not-exist | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | | (1 row) SELECT pg_stat_reset_replication_slot('do-not-exist'); ERROR: replication slot "do-not-exist" does not exist SELECT * FROM pg_stat_get_replication_slot('do-not-exist'); - slot_name | spill_txns | spill_count | spill_bytes | stream_txns | stream_count | stream_bytes | total_txns | total_bytes | stats_reset ---------------+------------+-------------+-------------+-------------+--------------+--------------+------------+-------------+------------- - do-not-exist | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | + slot_name | spill_txns | spill_count | spill_bytes | stream_txns | stream_count | stream_bytes | total_txns | total_bytes | slot_sync_skip_count | last_slot_sync_skip | stats_reset +--------------+------------+-------------+-------------+-------------+--------------+--------------+------------+-------------+----------------------+---------------------+------------- + do-not-exist | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | | (1 row) -- spilling the xact diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index 3f4a27a736e..65b1a8773f0 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -1644,6 +1644,26 @@ description | Waiting for a newly initialized WAL file to reach durable storage + + + slot_sync_skip_countbigint + + + Number of times the slot synchronization is skipped. + + + + + + + last_slot_sync_skiptimestamp with time zone + + + Time at which last slot synchronization was skipped. + + + + stats_reset timestamp with time zone diff --git a/doc/src/sgml/system-views.sgml b/doc/src/sgml/system-views.sgml index 4187191ea74..72e9b6de1e8 100644 --- a/doc/src/sgml/system-views.sgml +++ b/doc/src/sgml/system-views.sgml @@ -3036,6 +3036,14 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx + + + slot_sync_skip_reasontext + + + Reason of the last slot synchronization skip. + + diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql index c77fa0234bb..abca2f5f927 100644 --- a/src/backend/catalog/system_views.sql +++ b/src/backend/catalog/system_views.sql @@ -1046,7 +1046,8 @@ CREATE VIEW pg_replication_slots AS L.conflicting, L.invalidation_reason, L.failover, - L.synced + L.synced, + L.slot_sync_skip_reason FROM pg_get_replication_slots() AS L LEFT JOIN pg_database D ON (L.datoid = D.oid); @@ -1061,6 +1062,8 @@ CREATE VIEW pg_stat_replication_slots AS s.stream_bytes, s.total_txns, s.total_bytes, + s.slot_sync_skip_count, + s.last_slot_sync_skip, s.stats_reset FROM pg_replication_slots as r, LATERAL pg_stat_get_replication_slot(slot_name) as s diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c index 8c061d55bdb..6259fad894c 100644 --- a/src/backend/replication/logical/slotsync.c +++ b/src/backend/replication/logical/slotsync.c @@ -148,6 +148,24 @@ typedef struct RemoteSlot static void slotsync_failure_callback(int code, Datum arg); static void update_synced_slots_inactive_since(void); +/* Update slot sync skip stats */ +static void +update_slot_sync_skip_stats(ReplicationSlot *slot, SlotSyncSkipReason skip_reason) +{ + /* + * Update the slot sync related stats in pg_stat_replication_slot when a + * slot sync is skipped + */ + if (skip_reason != SS_SKIP_NONE) + pgstat_report_replslot_sync_skip(slot); + + /* Update the slot sync reason */ + SpinLockAcquire(&slot->mutex); + if (slot->slot_sync_skip_reason != skip_reason) + slot->slot_sync_skip_reason = skip_reason; + SpinLockRelease(&slot->mutex); +} + /* * If necessary, update the local synced slot's metadata based on the data * from the remote slot. @@ -218,6 +236,8 @@ update_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid, LSN_FORMAT_ARGS(slot->data.restart_lsn), slot->data.catalog_xmin)); + update_slot_sync_skip_stats(slot, SS_SKIP_REMOTE_BEHIND); + if (remote_slot_precedes) *remote_slot_precedes = true; @@ -337,6 +357,15 @@ update_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid, ReplicationSlotsComputeRequiredLSN(); } + /* + * If found_consistent_snapshot is not NULL and a consistent snapshot is + * found set the slot sync skip reason to none. Else, if consistent + * snapshot is not found the stats will be updated in the function + * update_and_persist_local_synced_slot + */ + if (!found_consistent_snapshot || *found_consistent_snapshot) + update_slot_sync_skip_stats(slot, SS_SKIP_NONE); + return updated_config || updated_xmin_or_lsn; } @@ -580,6 +609,9 @@ update_and_persist_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid) * current location when recreating the slot in the next cycle. It may * take more time to create such a slot. Therefore, we keep this slot * and attempt the synchronization in the next cycle. + * + * We do not need to update the slot sync skip stats here as it will + * be already updated in function update_local_synced_slot. */ return false; } @@ -595,11 +627,21 @@ update_and_persist_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid) errdetail("Synchronization could lead to data loss, because the standby could not build a consistent snapshot to decode WALs at LSN %X/%08X.", LSN_FORMAT_ARGS(slot->data.restart_lsn))); + /* + * If a consitent snapshot is not found, update the slot sync skip + * stats + */ + update_slot_sync_skip_stats(slot, SS_SKIP_NO_CONSISTENT_SNAPSHOT); + return false; } ReplicationSlotPersist(); + /* + * For the success case we do not update the slot sync skip stats here as + * it is already be updated in update_local_synced_slot. + */ ereport(LOG, errmsg("newly created replication slot \"%s\" is sync-ready now", remote_slot->name)); @@ -623,7 +665,7 @@ update_and_persist_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid) static bool synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid) { - ReplicationSlot *slot; + ReplicationSlot *slot = NULL; XLogRecPtr latestFlushPtr; bool slot_updated = false; @@ -634,6 +676,19 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid) latestFlushPtr = GetStandbyFlushRecPtr(NULL); if (remote_slot->confirmed_lsn > latestFlushPtr) { + /* If slot is present on the local, update the slot sync skip stats */ + if ((slot = SearchNamedReplicationSlot(remote_slot->name, true))) + { + bool synced; + + SpinLockAcquire(&slot->mutex); + synced = slot->data.synced; + SpinLockRelease(&slot->mutex); + + if (synced) + update_slot_sync_skip_stats(slot, SS_SKIP_MISSING_WAL_RECORD); + } + /* * Can get here only if GUC 'synchronized_standby_slots' on the * primary server was not configured correctly. @@ -650,7 +705,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid) } /* Search for the named slot */ - if ((slot = SearchNamedReplicationSlot(remote_slot->name, true))) + if (slot || (slot = SearchNamedReplicationSlot(remote_slot->name, true))) { bool synced; diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c index b8f21153e7b..4e03205c63b 100644 --- a/src/backend/replication/slotfuncs.c +++ b/src/backend/replication/slotfuncs.c @@ -228,6 +228,28 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS) PG_RETURN_VOID(); } +/* + * Map a SlotSyncSkipReason enum to a human-readable string + */ +static char * +GetSlotSyncSkipReason(SlotSyncSkipReason reason) +{ + switch (reason) + { + case SS_SKIP_NONE: + return "none"; + case SS_SKIP_REMOTE_BEHIND: + return "remote_behind"; + case SS_SKIP_MISSING_WAL_RECORD: + return "missing_wal_record"; + case SS_SKIP_NO_CONSISTENT_SNAPSHOT: + return "no_consistent_snapshot"; + } + + Assert(false); + return "none"; +} + /* * pg_get_replication_slots - SQL SRF showing all replication slots * that currently exist on the database cluster. @@ -235,7 +257,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS) Datum pg_get_replication_slots(PG_FUNCTION_ARGS) { -#define PG_GET_REPLICATION_SLOTS_COLS 20 +#define PG_GET_REPLICATION_SLOTS_COLS 21 ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo; XLogRecPtr currlsn; int slotno; @@ -443,6 +465,8 @@ pg_get_replication_slots(PG_FUNCTION_ARGS) values[i++] = BoolGetDatum(slot_contents.data.synced); + values[i++] = CStringGetTextDatum(GetSlotSyncSkipReason(slot_contents.slot_sync_skip_reason)); + Assert(i == PG_GET_REPLICATION_SLOTS_COLS); tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, diff --git a/src/backend/utils/activity/pgstat_replslot.c b/src/backend/utils/activity/pgstat_replslot.c index ccfb11c49bf..bf436472b8d 100644 --- a/src/backend/utils/activity/pgstat_replslot.c +++ b/src/backend/utils/activity/pgstat_replslot.c @@ -101,6 +101,31 @@ pgstat_report_replslot(ReplicationSlot *slot, const PgStat_StatReplSlotEntry *re pgstat_unlock_entry(entry_ref); } +/* + * Report replication slot sync skip statistics. + * + * We can rely on the stats for the slot to exist and to belong to this + * slot. We can only get here if pgstat_create_replslot() or + * pgstat_acquire_replslot() have already been called. + */ +void +pgstat_report_replslot_sync_skip(ReplicationSlot *slot) +{ + PgStat_EntryRef *entry_ref; + PgStatShared_ReplSlot *shstatent; + PgStat_StatReplSlotEntry *statent; + + entry_ref = pgstat_get_entry_ref_locked(PGSTAT_KIND_REPLSLOT, InvalidOid, + ReplicationSlotIndex(slot), false); + shstatent = (PgStatShared_ReplSlot *) entry_ref->shared_stats; + statent = &shstatent->stats; + + statent->slot_sync_skip_count += 1; + statent->last_slot_sync_skip = GetCurrentTimestamp(); + + pgstat_unlock_entry(entry_ref); +} + /* * Report replication slot creation. * diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c index c756c2bebaa..15500a77701 100644 --- a/src/backend/utils/adt/pgstatfuncs.c +++ b/src/backend/utils/adt/pgstatfuncs.c @@ -2100,7 +2100,7 @@ pg_stat_get_archiver(PG_FUNCTION_ARGS) Datum pg_stat_get_replication_slot(PG_FUNCTION_ARGS) { -#define PG_STAT_GET_REPLICATION_SLOT_COLS 10 +#define PG_STAT_GET_REPLICATION_SLOT_COLS 12 text *slotname_text = PG_GETARG_TEXT_P(0); NameData slotname; TupleDesc tupdesc; @@ -2129,7 +2129,11 @@ pg_stat_get_replication_slot(PG_FUNCTION_ARGS) INT8OID, -1, 0); TupleDescInitEntry(tupdesc, (AttrNumber) 9, "total_bytes", INT8OID, -1, 0); - TupleDescInitEntry(tupdesc, (AttrNumber) 10, "stats_reset", + TupleDescInitEntry(tupdesc, (AttrNumber) 10, "slot_sync_skip_count", + INT8OID, -1, 0); + TupleDescInitEntry(tupdesc, (AttrNumber) 11, "last_slot_sync_skip", + TIMESTAMPTZOID, -1, 0); + TupleDescInitEntry(tupdesc, (AttrNumber) 12, "stats_reset", TIMESTAMPTZOID, -1, 0); BlessTupleDesc(tupdesc); @@ -2154,11 +2158,17 @@ pg_stat_get_replication_slot(PG_FUNCTION_ARGS) values[6] = Int64GetDatum(slotent->stream_bytes); values[7] = Int64GetDatum(slotent->total_txns); values[8] = Int64GetDatum(slotent->total_bytes); + values[9] = Int64GetDatum(slotent->slot_sync_skip_count); + + if (slotent->last_slot_sync_skip == 0) + nulls[10] = true; + else + values[10] = TimestampTzGetDatum(slotent->last_slot_sync_skip); if (slotent->stat_reset_timestamp == 0) - nulls[9] = true; + nulls[11] = true; else - values[9] = TimestampTzGetDatum(slotent->stat_reset_timestamp); + values[11] = TimestampTzGetDatum(slotent->stat_reset_timestamp); /* Returns the record as Datum */ PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls))); diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat index 01eba3b5a19..649a6c0f78c 100644 --- a/src/include/catalog/pg_proc.dat +++ b/src/include/catalog/pg_proc.dat @@ -5687,9 +5687,9 @@ { oid => '6169', descr => 'statistics: information about replication slot', proname => 'pg_stat_get_replication_slot', provolatile => 's', proparallel => 'r', prorettype => 'record', proargtypes => 'text', - proallargtypes => '{text,text,int8,int8,int8,int8,int8,int8,int8,int8,timestamptz}', - proargmodes => '{i,o,o,o,o,o,o,o,o,o,o}', - proargnames => '{slot_name,slot_name,spill_txns,spill_count,spill_bytes,stream_txns,stream_count,stream_bytes,total_txns,total_bytes,stats_reset}', + proallargtypes => '{text,text,int8,int8,int8,int8,int8,int8,int8,int8,int8,timestamptz,timestamptz}', + proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o,o}', + proargnames => '{slot_name,slot_name,spill_txns,spill_count,spill_bytes,stream_txns,stream_count,stream_bytes,total_txns,total_bytes,slot_sync_skip_count,last_slot_sync_skip,stats_reset}', prosrc => 'pg_stat_get_replication_slot' }, { oid => '6230', descr => 'statistics: check if a stats object exists', @@ -11503,9 +11503,9 @@ proname => 'pg_get_replication_slots', prorows => '10', proisstrict => 'f', proretset => 't', provolatile => 's', prorettype => 'record', proargtypes => '', - proallargtypes => '{name,name,text,oid,bool,bool,int4,xid,xid,pg_lsn,pg_lsn,text,int8,bool,pg_lsn,timestamptz,bool,text,bool,bool}', - proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}', - proargnames => '{slot_name,plugin,slot_type,datoid,temporary,active,active_pid,xmin,catalog_xmin,restart_lsn,confirmed_flush_lsn,wal_status,safe_wal_size,two_phase,two_phase_at,inactive_since,conflicting,invalidation_reason,failover,synced}', + proallargtypes => '{name,name,text,oid,bool,bool,int4,xid,xid,pg_lsn,pg_lsn,text,int8,bool,pg_lsn,timestamptz,bool,text,bool,bool,text}', + proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}', + proargnames => '{slot_name,plugin,slot_type,datoid,temporary,active,active_pid,xmin,catalog_xmin,restart_lsn,confirmed_flush_lsn,wal_status,safe_wal_size,two_phase,two_phase_at,inactive_since,conflicting,invalidation_reason,failover,synced,slot_sync_skip_reason}', prosrc => 'pg_get_replication_slots' }, { oid => '3786', descr => 'set up a logical replication slot', proname => 'pg_create_logical_replication_slot', provolatile => 'v', diff --git a/src/include/pgstat.h b/src/include/pgstat.h index e4a59a30b8c..e9a506fa5bb 100644 --- a/src/include/pgstat.h +++ b/src/include/pgstat.h @@ -396,6 +396,8 @@ typedef struct PgStat_StatReplSlotEntry PgStat_Counter stream_bytes; PgStat_Counter total_txns; PgStat_Counter total_bytes; + PgStat_Counter slot_sync_skip_count; + TimestampTz last_slot_sync_skip; TimestampTz stat_reset_timestamp; } PgStat_StatReplSlotEntry; @@ -737,6 +739,7 @@ extern PgStat_TableStatus *find_tabstat_entry(Oid rel_id); extern void pgstat_reset_replslot(const char *name); struct ReplicationSlot; extern void pgstat_report_replslot(struct ReplicationSlot *slot, const PgStat_StatReplSlotEntry *repSlotStat); +extern void pgstat_report_replslot_sync_skip(struct ReplicationSlot *slot); extern void pgstat_create_replslot(struct ReplicationSlot *slot); extern void pgstat_acquire_replslot(struct ReplicationSlot *slot); extern void pgstat_drop_replslot(struct ReplicationSlot *slot); diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h index fe62162cde3..013f4bae942 100644 --- a/src/include/replication/slot.h +++ b/src/include/replication/slot.h @@ -71,6 +71,21 @@ typedef enum ReplicationSlotInvalidationCause /* Maximum number of invalidation causes */ #define RS_INVAL_MAX_CAUSES 4 +/* + * When slot sync worker is running or pg_sync_replication_slots is run, the + * slot sync can be skipped. This enum keeps a list of reasons of slot sync + * skip. + */ +typedef enum SlotSyncSkipReason +{ + SS_SKIP_NONE, /* No skip */ + SS_SKIP_MISSING_WAL_RECORD, /* Standby did not flush the wal coresponding + * to confirmed flush on remote slot */ + SS_SKIP_REMOTE_BEHIND, /* Remote slot is behind the local slot */ + SS_SKIP_NO_CONSISTENT_SNAPSHOT /* Standby could not build a consistent + * snapshot */ +} SlotSyncSkipReason; + /* * On-Disk data of a replication slot, preserved across restarts. */ @@ -249,6 +264,9 @@ typedef struct ReplicationSlot */ XLogRecPtr last_saved_restart_lsn; + /* The reason for last slot sync skip */ + SlotSyncSkipReason slot_sync_skip_reason; + } ReplicationSlot; #define SlotIsPhysical(slot) ((slot)->data.database == InvalidOid) diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out index 35e8aad7701..041d3328328 100644 --- a/src/test/regress/expected/rules.out +++ b/src/test/regress/expected/rules.out @@ -1499,8 +1499,9 @@ pg_replication_slots| SELECT l.slot_name, l.conflicting, l.invalidation_reason, l.failover, - l.synced - FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, temporary, active, active_pid, xmin, catalog_xmin, restart_lsn, confirmed_flush_lsn, wal_status, safe_wal_size, two_phase, two_phase_at, inactive_since, conflicting, invalidation_reason, failover, synced) + l.synced, + l.slot_sync_skip_reason + FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, temporary, active, active_pid, xmin, catalog_xmin, restart_lsn, confirmed_flush_lsn, wal_status, safe_wal_size, two_phase, two_phase_at, inactive_since, conflicting, invalidation_reason, failover, synced, slot_sync_skip_reason) LEFT JOIN pg_database d ON ((l.datoid = d.oid))); pg_roles| SELECT pg_authid.rolname, pg_authid.rolsuper, @@ -2140,9 +2141,11 @@ pg_stat_replication_slots| SELECT s.slot_name, s.stream_bytes, s.total_txns, s.total_bytes, + s.slot_sync_skip_count, + s.last_slot_sync_skip, s.stats_reset FROM pg_replication_slots r, - LATERAL pg_stat_get_replication_slot((r.slot_name)::text) s(slot_name, spill_txns, spill_count, spill_bytes, stream_txns, stream_count, stream_bytes, total_txns, total_bytes, stats_reset) + LATERAL pg_stat_get_replication_slot((r.slot_name)::text) s(slot_name, spill_txns, spill_count, spill_bytes, stream_txns, stream_count, stream_bytes, total_txns, total_bytes, slot_sync_skip_count, last_slot_sync_skip, stats_reset) WHERE (r.datoid IS NOT NULL); pg_stat_slru| SELECT name, blks_zeroed, diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list index 3c80d49b67e..3509f40875e 100644 --- a/src/tools/pgindent/typedefs.list +++ b/src/tools/pgindent/typedefs.list @@ -2788,6 +2788,7 @@ SlabSlot SlotInvalidationCauseMap SlotNumber SlotSyncCtxStruct +SlotSyncSkipReason SlruCtl SlruCtlData SlruErrorCause -- 2.34.1