Fix incomplete backpatch of pg_multixact truncation changes to <= 9.2

alvherre · alvherre · commit 3d974e303da2 · 2013-12-02T13:28:10.000-03:00
The backpatch of a95335b to 9.2, 9.1 and 9.0 was incomplete, missing changes to xlog.c, primarily the call to TrimMultiXact(). Testing presumably didn't show a problem without these changes because TrimMultiXact() performs defense-in-depth work, which is not strictly necessary. It also missed moving StartupMultiXact() which would have been problematic if a restartpoing happened in exactly the wrong moment, causing a transient error. Andres Freund
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
@@ -5991,6 +5991,12 @@ StartupXLOG(void)
 	XLogCtl->ckptXidEpoch = checkPoint.nextXidEpoch;
 	XLogCtl->ckptXid = checkPoint.nextXid;
 
+	/*
+	 * Startup MultiXact.  We need to do this early because we need its state
+	 * initialized because we attempt truncation during restartpoints.
+	 */
+	StartupMultiXact();
+
 	/*
 	 * We must replay WAL entries using the same TimeLineID they were created
 	 * under, so temporarily adopt the TLI indicated by the checkpoint (see
@@ -6121,8 +6127,9 @@ StartupXLOG(void)
 			ProcArrayInitRecovery(ShmemVariableCache->nextXid);
 
 			/*
-			 * Startup commit log and subtrans only. Other SLRUs are not
-			 * maintained during recovery and need not be started yet.
+			 * Startup commit log and subtrans only. MultiXact has already
+			 * been started up and other SLRUs are not maintained during
+			 * recovery and need not be started yet.
 			 */
 			StartupCLOG();
 			StartupSUBTRANS(oldestActiveXID);
@@ -6593,7 +6600,7 @@ StartupXLOG(void)
 	/*
 	 * Perform end of recovery actions for any SLRUs that need it.
 	 */
-	StartupMultiXact();
+	TrimMultiXact();
 	TrimCLOG();
 
 	/* Reload shared-memory state for prepared transactions */
diff --git a/src/include/access/multixact.h b/src/include/access/multixact.h
@@ -59,6 +59,7 @@ extern Size MultiXactShmemSize(void);
 extern void MultiXactShmemInit(void);
 extern void BootStrapMultiXact(void);
 extern void StartupMultiXact(void);
+extern void TrimMultiXact(void);
 extern void ShutdownMultiXact(void);
 extern void MultiXactGetCheckptMulti(bool is_shutdown,
 						 MultiXactId *nextMulti,
