Add more debugging information when dropping twice pgstats entry

michaelpq · michaelpq · commit 2de059de2c2d · 2024-06-07T18:46:34.000+09:00
Floris Van Nee has reported a bug in the pgstats facility where a stats entry already dropped would get again dropped. This case should not happen, still the error generated did not offer any details about the stats entry getting dropped. This commit improves the error message generated to inform about the stats entry kind, database OID, object OID and refcount, which should help to debug more the problem reported. Bertrand Drouvot has been independently able to reach this error path while writing a new feature, and more details about the failure would have been helpful for debugging. Author: Andres Freund, Bertrand Drouvot Discussion: https://postgr.es/m/20240505160915.6boysum4f34siqct@awork3.anarazel.de Discussion: https://postgr.es/m/ZkM30paAD8Cr/Bix@ip-10-97-1-34.eu-west-3.compute.internal Backpatch-through: 15
diff --git a/src/backend/utils/activity/pgstat_shmem.c b/src/backend/utils/activity/pgstat_shmem.c
@@ -780,7 +780,11 @@ pgstat_drop_entry_internal(PgStatShared_HashEntry *shent,
 	 * backends to release their references.
 	 */
 	if (shent->dropped)
-		elog(ERROR, "can only drop stats once");
+		elog(ERROR,
+			 "trying to drop stats entry already dropped: kind=%s dboid=%u objoid=%u refcount=%u",
+			 pgstat_get_kind_info(shent->key.kind)->name,
+			 shent->key.dboid, shent->key.objoid,
+			 pg_atomic_read_u32(&shent->refcount));
 	shent->dropped = true;
 
 	/* release refcount marking entry as not dropped */
