From 475e235e051f8745bd55720370ba452a121d6b95 Mon Sep 17 00:00:00 2001 From: Shlok Kyal Date: Mon, 10 Mar 2025 10:53:35 +0530 Subject: [PATCH v7] Comment race condition in copy_replication_slot After copied slot is created there can be a race condition with function InvalidateObsoleteReplicationSlots, when the copied slot appear before source slot in array ReplicationSlotCtl->replication_slots. If just after slot creation, the source slot is invalidated due to some operation. The execution of InvalidateObsoleteReplicationSlots will wait for copy_replication_slot function to release the copied slot. Then the source slot will be invalidated. So, the copying of source slot is successful in this case. The wal_status of copied slot is set to lost immediately and hence will not have any harm. --- src/backend/replication/slotfuncs.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c index 16a35279037..2c710a9c180 100644 --- a/src/backend/replication/slotfuncs.c +++ b/src/backend/replication/slotfuncs.c @@ -756,7 +756,22 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot) plugin = NameStr(*(PG_GETARG_NAME(3))); } - /* Create new slot and acquire it */ + /* + * Create new slot and acquire it + * + * After slot is created there can be a race condition with function + * InvalidateObsoleteReplicationSlots, when the copied slot appear before + * source slot in array ReplicationSlotCtl->replication_slots. + * + * If just after slot creation, the source slot is invalidated due to + * some operation. The execution of InvalidateObsoleteReplicationSlots will + * wait for this function to release the copied slot. Then the source slot + * will be invalidated. So, the copying of source slot is successful in this + * case. + * + * The wal_status of copied slot is set to lost immediately and hence will + * not have any harm. + */ if (logical_slot) { /* -- 2.34.1