Make logging about multixact wraparound protection less chatty.

The original messaging design, introduced in commit 068cfadf9, seems too
chatty now that some time has elapsed since the bug fix; most installations
will be in good shape and don't really need a reminder about this on every
postmaster start.

Hence, arrange to suppress the "wraparound protections are now enabled"
message during startup (specifically, during the TrimMultiXact() call).
The message will still appear if protection becomes effective at some
later point.

Discussion: https://postgr.es/m/17211.1489189214@sss.pgh.pa.us

src/backend/access/transam/multixact.c

@@ -363,7 +363,7 @@ static void ExtendMultiXactOffset(MultiXactId multi);
 static void ExtendMultiXactMember(MultiXactOffset offset, int nmembers);
 static bool MultiXactOffsetWouldWrap(MultiXactOffset boundary,
 						 MultiXactOffset start, uint32 distance);
-static bool SetOffsetVacuumLimit(void);
+static bool SetOffsetVacuumLimit(bool is_startup);
 static bool find_multixact_start(MultiXactId multi, MultiXactOffset *result);
 static void WriteMZeroPageXlogRec(int pageno, uint8 info);
 static void WriteMTruncateXlogRec(Oid oldestMultiDB,
@@ -2095,7 +2095,7 @@ TrimMultiXact(void)
 	LWLockRelease(MultiXactGenLock);
 
 	/* Now compute how far away the next members wraparound is. */
-	SetMultiXactIdLimit(oldestMXact, oldestMXactDB);
+	SetMultiXactIdLimit(oldestMXact, oldestMXactDB, true);
 }
 
 /*
@@ -2186,9 +2186,13 @@ MultiXactSetNextMXact(MultiXactId nextMulti,
  * Determine the last safe MultiXactId to allocate given the currently oldest
  * datminmxid (ie, the oldest MultiXactId that might exist in any database
  * of our cluster), and the OID of the (or a) database with that value.
+ *
+ * is_startup is true when we are just starting the cluster, false when we
+ * are updating state in a running cluster.  This only affects log messages.
  */
 void
-SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
+SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
+					bool is_startup)
 {
 	MultiXactId multiVacLimit;
 	MultiXactId multiWarnLimit;
@@ -2277,7 +2281,7 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
 	Assert(!InRecovery);
 
 	/* Set limits for offset vacuum. */
-	needs_offset_vacuum = SetOffsetVacuumLimit();
+	needs_offset_vacuum = SetOffsetVacuumLimit(is_startup);
 
 	/*
 	 * If past the autovacuum force point, immediately signal an autovac
@@ -2370,7 +2374,7 @@ MultiXactAdvanceOldest(MultiXactId oldestMulti, Oid oldestMultiDB)
 	Assert(InRecovery);
 
 	if (MultiXactIdPrecedes(MultiXactState->oldestMultiXactId, oldestMulti))
-		SetMultiXactIdLimit(oldestMulti, oldestMultiDB);
+		SetMultiXactIdLimit(oldestMulti, oldestMultiDB, false);
 }
 
 /*
@@ -2537,7 +2541,7 @@ GetOldestMultiXactId(void)
  * otherwise.
  */
 static bool
-SetOffsetVacuumLimit(void)
+SetOffsetVacuumLimit(bool is_startup)
 {
 	MultiXactId oldestMultiXactId;
 	MultiXactId nextMXact;
@@ -2619,9 +2623,10 @@ SetOffsetVacuumLimit(void)
 		/* always leave one segment before the wraparound point */
 		offsetStopLimit -= (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT);
 
-		if (!prevOldestOffsetKnown && IsUnderPostmaster)
+		if (!prevOldestOffsetKnown && !is_startup)
 			ereport(LOG,
 					(errmsg("MultiXact member wraparound protections are now enabled")));
+
 		ereport(DEBUG1,
 		(errmsg("MultiXact member stop limit is now %u based on MultiXact %u",
 				offsetStopLimit, oldestMultiXactId)));
@@ -3312,7 +3317,7 @@ multixact_redo(XLogReaderState *record)
 		 * Advance the horizon values, so they're current at the end of
 		 * recovery.
 		 */
-		SetMultiXactIdLimit(xlrec.endTruncOff, xlrec.oldestMultiDB);
+		SetMultiXactIdLimit(xlrec.endTruncOff, xlrec.oldestMultiDB, false);
 
 		PerformMembersTruncation(xlrec.startTruncMemb, xlrec.endTruncMemb);
 

src/backend/access/transam/xlog.c

@@ -4995,7 +4995,7 @@ BootStrapXLOG(void)
 	ShmemVariableCache->oidCount = 0;
 	MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
 	SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
-	SetMultiXactIdLimit(checkPoint.oldestMulti, checkPoint.oldestMultiDB);
+	SetMultiXactIdLimit(checkPoint.oldestMulti, checkPoint.oldestMultiDB, true);
 	SetCommitTsLimit(InvalidTransactionId, InvalidTransactionId);
 
 	/* Set up the XLOG page header */
@@ -6597,7 +6597,7 @@ StartupXLOG(void)
 	ShmemVariableCache->oidCount = 0;
 	MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
 	SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
-	SetMultiXactIdLimit(checkPoint.oldestMulti, checkPoint.oldestMultiDB);
+	SetMultiXactIdLimit(checkPoint.oldestMulti, checkPoint.oldestMultiDB, true);
 	SetCommitTsLimit(checkPoint.oldestCommitTsXid,
 					 checkPoint.newestCommitTsXid);
 	XLogCtl->ckptXidEpoch = checkPoint.nextXidEpoch;

src/backend/commands/vacuum.c

@@ -1205,7 +1205,7 @@ vac_truncate_clog(TransactionId frozenXID,
 	 * signalling twice?
 	 */
 	SetTransactionIdLimit(frozenXID, oldestxid_datoid);
-	SetMultiXactIdLimit(minMulti, minmulti_datoid);
+	SetMultiXactIdLimit(minMulti, minmulti_datoid, false);
 }
 
 

src/include/access/multixact.h

@@ -127,7 +127,8 @@ extern void StartupMultiXact(void);
 extern void TrimMultiXact(void);
 extern void ShutdownMultiXact(void);
 extern void SetMultiXactIdLimit(MultiXactId oldest_datminmxid,
-					Oid oldest_datoid);
+					Oid oldest_datoid,
+					bool is_startup);
 extern void MultiXactGetCheckptMulti(bool is_shutdown,
 						 MultiXactId *nextMulti,
 						 MultiXactOffset *nextMultiOffset,