From d851bef2d60ff9345249ff67c053e37fe4b364cc Mon Sep 17 00:00:00 2001 From: Simon Riggs Date: Mon, 5 Sep 2016 09:44:38 +0100 Subject: Dirty replication slots when using sql interface When pg_logical_slot_get_changes(...) sets confirmed_flush_lsn to the point at which replay stopped, it doesn't dirty the replication slot. So if the replay didn't cause restart_lsn or catalog_xmin to change as well, this change will not get written out to disk. Even on a clean shutdown. If Pg crashes or restarts, a subsequent pg_logical_slot_get_changes(...) call will see the same changes already replayed since it uses the slot's confirmed_flush_lsn as the start point for fetching changes. The caller can't specify a start LSN when using the SQL interface. Mark the slot as dirty after reading changes using the SQL interface so that users won't see repeated changes after a clean shutdown. Repeated changes still occur when using the walsender interface or after an unclean shutdown. Craig Ringer --- src/backend/replication/logical/logicalfuncs.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'src/backend/replication/logical/logicalfuncs.c') diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c index 4e4c8cdaeb2..9c7be2dc7b6 100644 --- a/src/backend/replication/logical/logicalfuncs.c +++ b/src/backend/replication/logical/logicalfuncs.c @@ -321,7 +321,22 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin * business..) */ if (ctx->reader->EndRecPtr != InvalidXLogRecPtr && confirm) + { LogicalConfirmReceivedLocation(ctx->reader->EndRecPtr); + /* + * If only the confirmed_flush_lsn has changed the slot won't get + * marked as dirty by the above. Callers on the walsender interface + * are expected to keep track of their own progress and don't need + * it written out. But SQL-interface users cannot specify their own + * start positions and it's harder for them to keep track of their + * progress, so we should make more of an effort to save it for them. + * + * Dirty the slot so it's written out at the next checkpoint. We'll + * still lose its position on crash, as documented, but it's better + * than always losing the position even on clean restart. + */ + ReplicationSlotMarkDirty(); + } /* free context, call shutdown callback */ FreeDecodingContext(ctx); -- cgit v1.2.3