Fix snapshot handling bug in recent BRIN fix

Commit a95e3d84c0e0 added ActiveSnapshot push+pop when processing
work-items (BRIN autosummarization), but forgot to handle the case of
a transaction failing during the run, which drops the snapshot untimely.
Fix by making the pop conditional on an element being actually there.

Author: Álvaro Herrera <alvherre@kurilemu.de>
Backpatch-through: 13
Discussion: https://postgr.es/m/202511041648.nofajnuddmwk@alvherre.pgsql

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index a967f5323d7d82ddef8391e3d36c252f625e2f06..d0931ee5c0fae6aa19d4f719e5ddd89bc0383bee 100644 (file)
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2625,7 +2625,8 @@ deleted:
 
                PushActiveSnapshot(GetTransactionSnapshot());
                perform_work_item(workitem);
-               PopActiveSnapshot();
+               if (ActiveSnapshotSet())        /* transaction could have aborted */
+                       PopActiveSnapshot();
 
                /*
                 * Check for config changes before acquiring lock for further jobs.