From 41fb3f51cb74eca1ba959ccd2fb1c0d7fe0bf11b Mon Sep 17 00:00:00 2001 From: Amit Kapila Date: Fri, 1 Aug 2025 07:16:30 +0000 Subject: [PATCH] Fix a deadlock during ALTER SUBSCRIPTION ... DROP PUBLICATION. A deadlock can occur when the DDL command and the apply worker acquire catalog locks in different orders while dropping replication origins. The issue is rare in PG16 and higher branches because, in most cases, the tablesync worker performs the origin drop in those branches, and its locking sequence does not conflict with DDL operations. This patch ensures consistent lock acquisition to prevent such deadlocks. As per buildfarm. Reported-by: Alexander Lakhin Author: Ajin Cherian Reviewed-by: Hayato Kuroda Reviewed-by: vignesh C Reviewed-by: Amit Kapila Backpatch-through: 14, where it was introduced Discussion: https://postgr.es/m/bab95e12-6cc5-4ebb-80a8-3e41956aa297@gmail.com --- src/backend/catalog/pg_subscription.c | 33 ++++++++++++++++++--- src/backend/replication/logical/tablesync.c | 27 +++++++++++++++-- src/include/catalog/pg_subscription_rel.h | 2 ++ 3 files changed, 55 insertions(+), 7 deletions(-) diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c index 29fc4218cd4..941817c8271 100644 --- a/src/backend/catalog/pg_subscription.c +++ b/src/backend/catalog/pg_subscription.c @@ -281,8 +281,8 @@ AddSubscriptionRelState(Oid subid, Oid relid, char state, * Update the state of a subscription table. */ void -UpdateSubscriptionRelState(Oid subid, Oid relid, char state, - XLogRecPtr sublsn) +UpdateSubscriptionRelStateEx(Oid subid, Oid relid, char state, + XLogRecPtr sublsn, bool already_locked) { Relation rel; HeapTuple tup; @@ -290,9 +290,24 @@ UpdateSubscriptionRelState(Oid subid, Oid relid, char state, Datum values[Natts_pg_subscription_rel]; bool replaces[Natts_pg_subscription_rel]; - LockSharedObject(SubscriptionRelationId, subid, 0, AccessShareLock); + if (already_locked) + { +#ifdef USE_ASSERT_CHECKING + LOCKTAG tag; - rel = table_open(SubscriptionRelRelationId, RowExclusiveLock); + Assert(CheckRelationOidLockedByMe(SubscriptionRelRelationId, + RowExclusiveLock, true)); + SET_LOCKTAG_OBJECT(tag, InvalidOid, SubscriptionRelationId, subid, 0); + Assert(LockHeldByMe(&tag, AccessShareLock)); +#endif + + rel = table_open(SubscriptionRelRelationId, NoLock); + } + else + { + LockSharedObject(SubscriptionRelationId, subid, 0, AccessShareLock); + rel = table_open(SubscriptionRelRelationId, RowExclusiveLock); + } /* Try finding existing mapping. */ tup = SearchSysCacheCopy2(SUBSCRIPTIONRELMAP, @@ -326,6 +341,16 @@ UpdateSubscriptionRelState(Oid subid, Oid relid, char state, table_close(rel, NoLock); } +/* + * Update the state of a subscription table. + */ +void +UpdateSubscriptionRelState(Oid subid, Oid relid, char state, + XLogRecPtr sublsn) +{ + UpdateSubscriptionRelStateEx(subid, relid, state, sublsn, false); +} + /* * Get state of subscription table. * diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c index 26b71dee672..3e9de50ff12 100644 --- a/src/backend/replication/logical/tablesync.c +++ b/src/backend/replication/logical/tablesync.c @@ -366,6 +366,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn) static HTAB *last_start_times = NULL; ListCell *lc; bool started_tx = false; + Relation rel = NULL; Assert(!IsTransactionState()); @@ -463,7 +464,16 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn) * refresh for the subscription where we remove the table * state and its origin and by this time the origin might be * already removed. So passing missing_ok = true. + * + * Lock the subscription and origin in the same order as we + * are doing during DDL commands to avoid deadlocks. See + * AlterSubscription_refresh. */ + LockSharedObject(SubscriptionRelationId, MyLogicalRepWorker->subid, + 0, AccessShareLock); + if (!rel) + rel = table_open(SubscriptionRelRelationId, RowExclusiveLock); + ReplicationOriginNameForTablesync(MyLogicalRepWorker->subid, rstate->relid, originname, @@ -473,9 +483,9 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn) /* * Update the state to READY only after the origin cleanup. */ - UpdateSubscriptionRelState(MyLogicalRepWorker->subid, - rstate->relid, rstate->state, - rstate->lsn); + UpdateSubscriptionRelStateEx(MyLogicalRepWorker->subid, + rstate->relid, rstate->state, + rstate->lsn, true); } } else @@ -526,7 +536,14 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn) * This is required to avoid any undetected deadlocks * due to any existing lock as deadlock detector won't * be able to detect the waits on the latch. + * + * Also close any tables prior to the commit. */ + if (rel) + { + table_close(rel, NoLock); + rel = NULL; + } CommitTransactionCommand(); pgstat_report_stat(false); } @@ -586,6 +603,10 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn) } } + /* Close table if opened */ + if (rel) + table_close(rel, NoLock); + if (started_tx) { CommitTransactionCommand(); diff --git a/src/include/catalog/pg_subscription_rel.h b/src/include/catalog/pg_subscription_rel.h index ed94f57baa1..e0a1a4b8b4a 100644 --- a/src/include/catalog/pg_subscription_rel.h +++ b/src/include/catalog/pg_subscription_rel.h @@ -85,6 +85,8 @@ extern void AddSubscriptionRelState(Oid subid, Oid relid, char state, XLogRecPtr sublsn); extern void UpdateSubscriptionRelState(Oid subid, Oid relid, char state, XLogRecPtr sublsn); +extern void UpdateSubscriptionRelStateEx(Oid subid, Oid relid, char state, + XLogRecPtr sublsn, bool already_locked); extern char GetSubscriptionRelState(Oid subid, Oid relid, XLogRecPtr *sublsn); extern void RemoveSubscriptionRel(Oid subid, Oid relid);