From 447aae13b0305780e87cac7b0dd669db6fab3d9d Mon Sep 17 00:00:00 2001 From: Alexander Korotkov Date: Wed, 5 Nov 2025 11:43:55 +0200 Subject: Implement WAIT FOR command MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit WAIT FOR is to be used on standby and specifies waiting for the specific WAL location to be replayed. This option is useful when the user makes some data changes on primary and needs a guarantee to see these changes are on standby. WAIT FOR needs to wait without any snapshot held. Otherwise, the snapshot could prevent the replay of WAL records, implying a kind of self-deadlock. This is why separate utility command seems appears to be the most robust way to implement this functionality. It's not possible to implement this as a function. Previous experience shows that stored procedures also have limitation in this aspect. Discussion: https://www.postgresql.org/message-id/flat/CAPpHfdsjtZLVzxjGT8rJHCYbM0D5dwkO+BBjcirozJ6nYbOW8Q@mail.gmail.com Discussion: https://www.postgresql.org/message-id/flat/CABPTF7UNft368x-RgOXkfj475OwEbp%2BVVO-wEXz7StgjD_%3D6sw%40mail.gmail.com Author: Kartyshov Ivan Author: Alexander Korotkov Author: Xuneng Zhou Reviewed-by: Michael Paquier Reviewed-by: Peter Eisentraut Reviewed-by: Dilip Kumar Reviewed-by: Amit Kapila Reviewed-by: Alexander Lakhin Reviewed-by: Bharath Rupireddy Reviewed-by: Euler Taveira Reviewed-by: Heikki Linnakangas Reviewed-by: Kyotaro Horiguchi Reviewed-by: jian he Reviewed-by: Álvaro Herrera Reviewed-by: Xuneng Zhou --- src/backend/tcop/pquery.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) (limited to 'src/backend/tcop/pquery.c') diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c index 74179139fa9..fde78c55160 100644 --- a/src/backend/tcop/pquery.c +++ b/src/backend/tcop/pquery.c @@ -1158,10 +1158,11 @@ PortalRunUtility(Portal portal, PlannedStmt *pstmt, MemoryContextSwitchTo(portal->portalContext); /* - * Some utility commands (e.g., VACUUM) pop the ActiveSnapshot stack from - * under us, so don't complain if it's now empty. Otherwise, our snapshot - * should be the top one; pop it. Note that this could be a different - * snapshot from the one we made above; see EnsurePortalSnapshotExists. + * Some utility commands (e.g., VACUUM, WAIT FOR) pop the ActiveSnapshot + * stack from under us, so don't complain if it's now empty. Otherwise, + * our snapshot should be the top one; pop it. Note that this could be a + * different snapshot from the one we made above; see + * EnsurePortalSnapshotExists. */ if (portal->portalSnapshot != NULL && ActiveSnapshotSet()) { @@ -1738,7 +1739,8 @@ PlannedStmtRequiresSnapshot(PlannedStmt *pstmt) IsA(utilityStmt, ListenStmt) || IsA(utilityStmt, NotifyStmt) || IsA(utilityStmt, UnlistenStmt) || - IsA(utilityStmt, CheckPointStmt)) + IsA(utilityStmt, CheckPointStmt) || + IsA(utilityStmt, WaitStmt)) return false; return true; -- cgit v1.2.3