From 8c75db3cfab921d495d7d97009f2cfef00f26d6f Mon Sep 17 00:00:00 2001 From: Dilip Kumar Date: Thu, 14 Aug 2025 07:19:49 +0000 Subject: [PATCH v4] Fix DROP SUBSCRIPTION deadlock with new database creation DROP SUBSCRIPTION previously acquired an AccessExclusiveLock on the pg_subscription catalog to prevent the replication launcher from starting a new worker. However, this caused a deadlock. New database creation also need to acquire an AccessShareLock on this same catalog during their initialization phase. This created a lock conflict where DROP SUBSCRIPTION would block this, while simultaneously waiting for a connection to complete for dropping the replication slot. This commit resolves the deadlock by having DROP SUBSCRIPTION acquire a less restrictive RowExclusiveLock on the catalog instead. To address the original concern of orphaned workers, a new check is implemented. The replication worker now takes a shared object lock on the subscription itself. If a worker starts for a subscription that no longer exists, it immediately detects this condition and exits. This ensures that no orphan workers are created without the need for an overly broad AccessExclusiveLock on the system catalog. --- src/backend/commands/subscriptioncmds.c | 8 +++++--- src/backend/replication/logical/worker.c | 7 +++++++ 2 files changed, 12 insertions(+), 3 deletions(-) diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c index 40356e97ed2..28ab74ece93 100644 --- a/src/backend/commands/subscriptioncmds.c +++ b/src/backend/commands/subscriptioncmds.c @@ -844,10 +844,12 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel) Form_pg_subscription form; /* - * Lock pg_subscription with AccessExclusiveLock to ensure that the - * launcher doesn't restart new worker during dropping the subscription + * The launcher may concurrently start a new worker for this subscription. + * During initialization, the worker checks for subscription validity and + * exits if the subscription has already been dropped. See + * InitializeLogRepWorker. */ - rel = table_open(SubscriptionRelationId, AccessExclusiveLock); + rel = table_open(SubscriptionRelationId, RowExclusiveLock); tup = SearchSysCache2(SUBSCRIPTIONNAME, MyDatabaseId, CStringGetDatum(stmt->subname)); diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c index a0e64301a94..b41738627ca 100644 --- a/src/backend/replication/logical/worker.c +++ b/src/backend/replication/logical/worker.c @@ -2070,6 +2070,13 @@ ApplyWorkerMain(Datum main_arg) StartTransactionCommand(); oldctx = MemoryContextSwitchTo(ApplyContext); + /* + * Lock the subscription to prevent it from being concurrently dropped, + * then re-verify its existence. After the initialization, the worker will + * be terminated gracefully if the subscription is dropped. + */ + LockSharedObject(SubscriptionRelationId, MyLogicalRepWorker->subid, 0, + AccessShareLock); MySubscription = GetSubscription(MyLogicalRepWorker->subid, true); if (!MySubscription) { -- 2.51.0.rc0.215.g125493bb4a-goog