Fix CheckPointReplicationSlots() with max_replication_slots == 0

akorotkov · akorotkov · commit 7195c804bd12 · 2025-06-27T11:49:00.000+03:00
ca307d5 made CheckPointReplicationSlots() unconditionally call ReplicationSlotsComputeRequiredLSN(). It causes an assertion trap when max_replication_slots equals 0. This commit makes CheckPointReplicationSlots() call ReplicationSlotsComputeRequiredLSN() only when at least one slot gets its last_saved_restart_lsn updated. That avoids an assert trap and also saves some cycles when no one slot has last_saved_restart_lsn updated. Based on ideas from Dilip Kumar <dilipbalaut@gmail.com> and Hayato Kuroda <kuroda.hayato@fujitsu.com>. Reported-by: Zhijie Hou <houzj.fnst@fujitsu.com> Discussion: https://postgr.es/m/OS0PR01MB5716BB506AF934376FF3A8BB947BA%40OS0PR01MB5716.jpnprd01.prod.outlook.com
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
@@ -2079,6 +2079,7 @@ void
 CheckPointReplicationSlots(bool is_shutdown)
 {
 	int			i;
+	bool		last_saved_restart_lsn_updated = false;
 
 	elog(DEBUG1, "performing replication slot checkpoint");
 
@@ -2123,15 +2124,23 @@ CheckPointReplicationSlots(bool is_shutdown)
 			SpinLockRelease(&s->mutex);
 		}
 
+		/*
+		 * Track if we're going to update slot's last_saved_restart_lsn. We
+		 * need this to know if we need to recompute the required LSN.
+		 */
+		if (s->last_saved_restart_lsn != s->data.restart_lsn)
+			last_saved_restart_lsn_updated = true;
+
 		SaveSlotToPath(s, path, LOG);
 	}
 	LWLockRelease(ReplicationSlotAllocationLock);
 
 	/*
-	 * Recompute the required LSN as SaveSlotToPath() updated
-	 * last_saved_restart_lsn for slots.
+	 * Recompute the required LSN if SaveSlotToPath() updated
+	 * last_saved_restart_lsn for any slot.
 	 */
-	ReplicationSlotsComputeRequiredLSN();
+	if (last_saved_restart_lsn_updated)
+		ReplicationSlotsComputeRequiredLSN();
 }
 
 /*
