Rename ShmemVariableCache to TransamVariables

The old name was misleading: It's not a cache, the values kept in the
struct are the authoritative source.

Reviewed-by: Tristan Partin, Richard Guo
Discussion: https://www.postgresql.org/message-id/6537d63d-4bb5-46f8-9b5d-73a8ba4720ab@iki.fi

src/backend/access/transam/clog.c

@@ -758,12 +758,12 @@ ZeroCLOGPage(int64 pageno, bool writeXlog)
 
 /*
  * This must be called ONCE during postmaster or standalone-backend startup,
- * after StartupXLOG has initialized ShmemVariableCache->nextXid.
+ * after StartupXLOG has initialized TransamVariables->nextXid.
  */
 void
 StartupCLOG(void)
 {
-	TransactionId xid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
+	TransactionId xid = XidFromFullTransactionId(TransamVariables->nextXid);
 	int64		pageno = TransactionIdToPage(xid);
 
 	LWLockAcquire(XactSLRULock, LW_EXCLUSIVE);
@@ -782,7 +782,7 @@ StartupCLOG(void)
 void
 TrimCLOG(void)
 {
-	TransactionId xid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
+	TransactionId xid = XidFromFullTransactionId(TransamVariables->nextXid);
 	int64		pageno = TransactionIdToPage(xid);
 
 	LWLockAcquire(XactSLRULock, LW_EXCLUSIVE);

src/backend/access/transam/commit_ts.c

@@ -211,8 +211,8 @@ TransactionTreeSetCommitTsData(TransactionId xid, int nsubxids,
 	commitTsShared->dataLastCommit.nodeid = nodeid;
 
 	/* and move forwards our endpoint, if needed */
-	if (TransactionIdPrecedes(ShmemVariableCache->newestCommitTsXid, newestXact))
-		ShmemVariableCache->newestCommitTsXid = newestXact;
+	if (TransactionIdPrecedes(TransamVariables->newestCommitTsXid, newestXact))
+		TransamVariables->newestCommitTsXid = newestXact;
 	LWLockRelease(CommitTsLock);
 }
 
@@ -315,8 +315,8 @@ TransactionIdGetCommitTsData(TransactionId xid, TimestampTz *ts,
 		return *ts != 0;
 	}
 
-	oldestCommitTsXid = ShmemVariableCache->oldestCommitTsXid;
-	newestCommitTsXid = ShmemVariableCache->newestCommitTsXid;
+	oldestCommitTsXid = TransamVariables->oldestCommitTsXid;
+	newestCommitTsXid = TransamVariables->newestCommitTsXid;
 	/* neither is invalid, or both are */
 	Assert(TransactionIdIsValid(oldestCommitTsXid) == TransactionIdIsValid(newestCommitTsXid));
 	LWLockRelease(CommitTsLock);
@@ -593,7 +593,7 @@ ZeroCommitTsPage(int64 pageno, bool writeXlog)
 
 /*
  * This must be called ONCE during postmaster or standalone-backend startup,
- * after StartupXLOG has initialized ShmemVariableCache->nextXid.
+ * after StartupXLOG has initialized TransamVariables->nextXid.
  */
 void
 StartupCommitTs(void)
@@ -683,7 +683,7 @@ ActivateCommitTs(void)
 	}
 	LWLockRelease(CommitTsLock);
 
-	xid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
+	xid = XidFromFullTransactionId(TransamVariables->nextXid);
 	pageno = TransactionIdToCTsPage(xid);
 
 	/*
@@ -707,10 +707,10 @@ ActivateCommitTs(void)
 	 * Invalid temporarily.
 	 */
 	LWLockAcquire(CommitTsLock, LW_EXCLUSIVE);
-	if (ShmemVariableCache->oldestCommitTsXid == InvalidTransactionId)
+	if (TransamVariables->oldestCommitTsXid == InvalidTransactionId)
 	{
-		ShmemVariableCache->oldestCommitTsXid =
-			ShmemVariableCache->newestCommitTsXid = ReadNextTransactionId();
+		TransamVariables->oldestCommitTsXid =
+			TransamVariables->newestCommitTsXid = ReadNextTransactionId();
 	}
 	LWLockRelease(CommitTsLock);
 
@@ -759,8 +759,8 @@ DeactivateCommitTs(void)
 	TIMESTAMP_NOBEGIN(commitTsShared->dataLastCommit.time);
 	commitTsShared->dataLastCommit.nodeid = InvalidRepOriginId;
 
-	ShmemVariableCache->oldestCommitTsXid = InvalidTransactionId;
-	ShmemVariableCache->newestCommitTsXid = InvalidTransactionId;
+	TransamVariables->oldestCommitTsXid = InvalidTransactionId;
+	TransamVariables->newestCommitTsXid = InvalidTransactionId;
 
 	LWLockRelease(CommitTsLock);
 
@@ -874,18 +874,18 @@ SetCommitTsLimit(TransactionId oldestXact, TransactionId newestXact)
 	 * "future" or signal a disabled committs.
 	 */
 	LWLockAcquire(CommitTsLock, LW_EXCLUSIVE);
-	if (ShmemVariableCache->oldestCommitTsXid != InvalidTransactionId)
+	if (TransamVariables->oldestCommitTsXid != InvalidTransactionId)
 	{
-		if (TransactionIdPrecedes(ShmemVariableCache->oldestCommitTsXid, oldestXact))
-			ShmemVariableCache->oldestCommitTsXid = oldestXact;
-		if (TransactionIdPrecedes(newestXact, ShmemVariableCache->newestCommitTsXid))
-			ShmemVariableCache->newestCommitTsXid = newestXact;
+		if (TransactionIdPrecedes(TransamVariables->oldestCommitTsXid, oldestXact))
+			TransamVariables->oldestCommitTsXid = oldestXact;
+		if (TransactionIdPrecedes(newestXact, TransamVariables->newestCommitTsXid))
+			TransamVariables->newestCommitTsXid = newestXact;
 	}
 	else
 	{
-		Assert(ShmemVariableCache->newestCommitTsXid == InvalidTransactionId);
-		ShmemVariableCache->oldestCommitTsXid = oldestXact;
-		ShmemVariableCache->newestCommitTsXid = newestXact;
+		Assert(TransamVariables->newestCommitTsXid == InvalidTransactionId);
+		TransamVariables->oldestCommitTsXid = oldestXact;
+		TransamVariables->newestCommitTsXid = newestXact;
 	}
 	LWLockRelease(CommitTsLock);
 }
@@ -897,9 +897,9 @@ void
 AdvanceOldestCommitTsXid(TransactionId oldestXact)
 {
 	LWLockAcquire(CommitTsLock, LW_EXCLUSIVE);
-	if (ShmemVariableCache->oldestCommitTsXid != InvalidTransactionId &&
-		TransactionIdPrecedes(ShmemVariableCache->oldestCommitTsXid, oldestXact))
-		ShmemVariableCache->oldestCommitTsXid = oldestXact;
+	if (TransamVariables->oldestCommitTsXid != InvalidTransactionId &&
+		TransactionIdPrecedes(TransamVariables->oldestCommitTsXid, oldestXact))
+		TransamVariables->oldestCommitTsXid = oldestXact;
 	LWLockRelease(CommitTsLock);
 }
 

src/backend/access/transam/subtrans.c

@@ -250,7 +250,7 @@ ZeroSUBTRANSPage(int64 pageno)
 
 /*
  * This must be called ONCE during postmaster or standalone-backend startup,
- * after StartupXLOG has initialized ShmemVariableCache->nextXid.
+ * after StartupXLOG has initialized TransamVariables->nextXid.
  *
  * oldestActiveXID is the oldest XID of any prepared transaction, or nextXid
  * if there are none.
@@ -271,7 +271,7 @@ StartupSUBTRANS(TransactionId oldestActiveXID)
 	LWLockAcquire(SubtransSLRULock, LW_EXCLUSIVE);
 
 	startPage = TransactionIdToPage(oldestActiveXID);
-	nextXid = ShmemVariableCache->nextXid;
+	nextXid = TransamVariables->nextXid;
 	endPage = TransactionIdToPage(XidFromFullTransactionId(nextXid));
 
 	while (startPage != endPage)

src/backend/access/transam/twophase.c

@@ -958,7 +958,7 @@ AdjustToFullTransactionId(TransactionId xid)
 	Assert(TransactionIdIsValid(xid));
 
 	LWLockAcquire(XidGenLock, LW_SHARED);
-	nextFullXid = ShmemVariableCache->nextXid;
+	nextFullXid = TransamVariables->nextXid;
 	LWLockRelease(XidGenLock);
 
 	nextXid = XidFromFullTransactionId(nextFullXid);
@@ -1948,7 +1948,7 @@ restoreTwoPhaseData(void)
  *
  * Scan the shared memory entries of TwoPhaseState and determine the range
  * of valid XIDs present.  This is run during database startup, after we
- * have completed reading WAL.  ShmemVariableCache->nextXid has been set to
+ * have completed reading WAL.  TransamVariables->nextXid has been set to
  * one more than the highest XID for which evidence exists in WAL.
  *
  * We throw away any prepared xacts with main XID beyond nextXid --- if any
@@ -1967,7 +1967,7 @@ restoreTwoPhaseData(void)
  * backup should be rolled in.
  *
  * Our other responsibility is to determine and return the oldest valid XID
- * among the prepared xacts (if none, return ShmemVariableCache->nextXid).
+ * among the prepared xacts (if none, return TransamVariables->nextXid).
  * This is needed to synchronize pg_subtrans startup properly.
  *
  * If xids_p and nxids_p are not NULL, pointer to a palloc'd array of all
@@ -1977,7 +1977,7 @@ restoreTwoPhaseData(void)
 TransactionId
 PrescanPreparedTransactions(TransactionId **xids_p, int *nxids_p)
 {
-	FullTransactionId nextXid = ShmemVariableCache->nextXid;
+	FullTransactionId nextXid = TransamVariables->nextXid;
 	TransactionId origNextXid = XidFromFullTransactionId(nextXid);
 	TransactionId result = origNextXid;
 	TransactionId *xids = NULL;
@@ -2196,7 +2196,7 @@ RecoverPreparedTransactions(void)
  *
  * If setParent is true, set up subtransaction parent linkages.
  *
- * If setNextXid is true, set ShmemVariableCache->nextXid to the newest
+ * If setNextXid is true, set TransamVariables->nextXid to the newest
  * value scanned.
  */
 static char *
@@ -2205,7 +2205,7 @@ ProcessTwoPhaseBuffer(TransactionId xid,
 					  bool fromdisk,
 					  bool setParent, bool setNextXid)
 {
-	FullTransactionId nextXid = ShmemVariableCache->nextXid;
+	FullTransactionId nextXid = TransamVariables->nextXid;
 	TransactionId origNextXid = XidFromFullTransactionId(nextXid);
 	TransactionId *subxids;
 	char	   *buf;

src/backend/access/transam/varsup.c

@@ -30,17 +30,17 @@
 /* Number of OIDs to prefetch (preallocate) per XLOG write */
 #define VAR_OID_PREFETCH		8192
 
-/* pointer to "variable cache" in shared memory (set up by shmem.c) */
-VariableCache ShmemVariableCache = NULL;
+/* pointer to variables struct in shared memory */
+TransamVariablesData *TransamVariables = NULL;
 
 
 /*
- * Initialization of shared memory for ShmemVariableCache.
+ * Initialization of shared memory for TransamVariables.
  */
 Size
 VarsupShmemSize(void)
 {
-	return sizeof(VariableCacheData);
+	return sizeof(TransamVariablesData);
 }
 
 void
@@ -49,13 +49,13 @@ VarsupShmemInit(void)
 	bool		found;
 
 	/* Initialize our shared state struct */
-	ShmemVariableCache = ShmemInitStruct("ShmemVariableCache",
-										 sizeof(VariableCacheData),
-										 &found);
+	TransamVariables = ShmemInitStruct("TransamVariables",
+									   sizeof(TransamVariablesData),
+									   &found);
 	if (!IsUnderPostmaster)
 	{
 		Assert(!found);
-		memset(ShmemVariableCache, 0, sizeof(VariableCacheData));
+		memset(TransamVariables, 0, sizeof(TransamVariablesData));
 	}
 	else
 		Assert(found);
@@ -104,7 +104,7 @@ GetNewTransactionId(bool isSubXact)
 
 	LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
 
-	full_xid = ShmemVariableCache->nextXid;
+	full_xid = TransamVariables->nextXid;
 	xid = XidFromFullTransactionId(full_xid);
 
 	/*----------
@@ -120,7 +120,7 @@ GetNewTransactionId(bool isSubXact)
 	 * Note that this coding also appears in GetNewMultiXactId.
 	 *----------
 	 */
-	if (TransactionIdFollowsOrEquals(xid, ShmemVariableCache->xidVacLimit))
+	if (TransactionIdFollowsOrEquals(xid, TransamVariables->xidVacLimit))
 	{
 		/*
 		 * For safety's sake, we release XidGenLock while sending signals,
@@ -129,10 +129,10 @@ GetNewTransactionId(bool isSubXact)
 		 * possibility of deadlock while doing get_database_name(). First,
 		 * copy all the shared values we'll need in this path.
 		 */
-		TransactionId xidWarnLimit = ShmemVariableCache->xidWarnLimit;
-		TransactionId xidStopLimit = ShmemVariableCache->xidStopLimit;
-		TransactionId xidWrapLimit = ShmemVariableCache->xidWrapLimit;
-		Oid			oldest_datoid = ShmemVariableCache->oldestXidDB;
+		TransactionId xidWarnLimit = TransamVariables->xidWarnLimit;
+		TransactionId xidStopLimit = TransamVariables->xidStopLimit;
+		TransactionId xidWrapLimit = TransamVariables->xidWrapLimit;
+		Oid			oldest_datoid = TransamVariables->oldestXidDB;
 
 		LWLockRelease(XidGenLock);
 
@@ -188,7 +188,7 @@ GetNewTransactionId(bool isSubXact)
 
 		/* Re-acquire lock and start over */
 		LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
-		full_xid = ShmemVariableCache->nextXid;
+		full_xid = TransamVariables->nextXid;
 		xid = XidFromFullTransactionId(full_xid);
 	}
 
@@ -211,7 +211,7 @@ GetNewTransactionId(bool isSubXact)
 	 * want the next incoming transaction to try it again.  We cannot assign
 	 * more XIDs until there is CLOG space for them.
 	 */
-	FullTransactionIdAdvance(&ShmemVariableCache->nextXid);
+	FullTransactionIdAdvance(&TransamVariables->nextXid);
 
 	/*
 	 * We must store the new XID into the shared ProcArray before releasing
@@ -290,7 +290,7 @@ ReadNextFullTransactionId(void)
 	FullTransactionId fullXid;
 
 	LWLockAcquire(XidGenLock, LW_SHARED);
-	fullXid = ShmemVariableCache->nextXid;
+	fullXid = TransamVariables->nextXid;
 	LWLockRelease(XidGenLock);
 
 	return fullXid;
@@ -315,7 +315,7 @@ AdvanceNextFullTransactionIdPastXid(TransactionId xid)
 	Assert(AmStartupProcess() || !IsUnderPostmaster);
 
 	/* Fast return if this isn't an xid high enough to move the needle. */
-	next_xid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
+	next_xid = XidFromFullTransactionId(TransamVariables->nextXid);
 	if (!TransactionIdFollowsOrEquals(xid, next_xid))
 		return;
 
@@ -328,7 +328,7 @@ AdvanceNextFullTransactionIdPastXid(TransactionId xid)
 	 * point in the WAL stream.
 	 */
 	TransactionIdAdvance(xid);
-	epoch = EpochFromFullTransactionId(ShmemVariableCache->nextXid);
+	epoch = EpochFromFullTransactionId(TransamVariables->nextXid);
 	if (unlikely(xid < next_xid))
 		++epoch;
 	newNextFullXid = FullTransactionIdFromEpochAndXid(epoch, xid);
@@ -338,7 +338,7 @@ AdvanceNextFullTransactionIdPastXid(TransactionId xid)
 	 * concurrent readers.
 	 */
 	LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
-	ShmemVariableCache->nextXid = newNextFullXid;
+	TransamVariables->nextXid = newNextFullXid;
 	LWLockRelease(XidGenLock);
 }
 
@@ -355,10 +355,10 @@ void
 AdvanceOldestClogXid(TransactionId oldest_datfrozenxid)
 {
 	LWLockAcquire(XactTruncationLock, LW_EXCLUSIVE);
-	if (TransactionIdPrecedes(ShmemVariableCache->oldestClogXid,
+	if (TransactionIdPrecedes(TransamVariables->oldestClogXid,
 							  oldest_datfrozenxid))
 	{
-		ShmemVariableCache->oldestClogXid = oldest_datfrozenxid;
+		TransamVariables->oldestClogXid = oldest_datfrozenxid;
 	}
 	LWLockRelease(XactTruncationLock);
 }
@@ -441,13 +441,13 @@ SetTransactionIdLimit(TransactionId oldest_datfrozenxid, Oid oldest_datoid)
 
 	/* Grab lock for just long enough to set the new limit values */
 	LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
-	ShmemVariableCache->oldestXid = oldest_datfrozenxid;
-	ShmemVariableCache->xidVacLimit = xidVacLimit;
-	ShmemVariableCache->xidWarnLimit = xidWarnLimit;
-	ShmemVariableCache->xidStopLimit = xidStopLimit;
-	ShmemVariableCache->xidWrapLimit = xidWrapLimit;
-	ShmemVariableCache->oldestXidDB = oldest_datoid;
-	curXid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
+	TransamVariables->oldestXid = oldest_datfrozenxid;
+	TransamVariables->xidVacLimit = xidVacLimit;
+	TransamVariables->xidWarnLimit = xidWarnLimit;
+	TransamVariables->xidStopLimit = xidStopLimit;
+	TransamVariables->xidWrapLimit = xidWrapLimit;
+	TransamVariables->oldestXidDB = oldest_datoid;
+	curXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	LWLockRelease(XidGenLock);
 
 	/* Log the info */
@@ -523,10 +523,10 @@ ForceTransactionIdLimitUpdate(void)
 
 	/* Locking is probably not really necessary, but let's be careful */
 	LWLockAcquire(XidGenLock, LW_SHARED);
-	nextXid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
-	xidVacLimit = ShmemVariableCache->xidVacLimit;
-	oldestXid = ShmemVariableCache->oldestXid;
-	oldestXidDB = ShmemVariableCache->oldestXidDB;
+	nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
+	xidVacLimit = TransamVariables->xidVacLimit;
+	oldestXid = TransamVariables->oldestXid;
+	oldestXidDB = TransamVariables->oldestXidDB;
 	LWLockRelease(XidGenLock);
 
 	if (!TransactionIdIsNormal(oldestXid))
@@ -576,37 +576,37 @@ GetNewObjectId(void)
 	 * available for automatic assignment during initdb, while ensuring they
 	 * will never conflict with user-assigned OIDs.
 	 */
-	if (ShmemVariableCache->nextOid < ((Oid) FirstNormalObjectId))
+	if (TransamVariables->nextOid < ((Oid) FirstNormalObjectId))
 	{
 		if (IsPostmasterEnvironment)
 		{
 			/* wraparound, or first post-initdb assignment, in normal mode */
-			ShmemVariableCache->nextOid = FirstNormalObjectId;
-			ShmemVariableCache->oidCount = 0;
+			TransamVariables->nextOid = FirstNormalObjectId;
+			TransamVariables->oidCount = 0;
 		}
 		else
 		{
 			/* we may be bootstrapping, so don't enforce the full range */
-			if (ShmemVariableCache->nextOid < ((Oid) FirstGenbkiObjectId))
+			if (TransamVariables->nextOid < ((Oid) FirstGenbkiObjectId))
 			{
 				/* wraparound in standalone mode (unlikely but possible) */
-				ShmemVariableCache->nextOid = FirstNormalObjectId;
-				ShmemVariableCache->oidCount = 0;
+				TransamVariables->nextOid = FirstNormalObjectId;
+				TransamVariables->oidCount = 0;
 			}
 		}
 	}
 
 	/* If we run out of logged for use oids then we must log more */
-	if (ShmemVariableCache->oidCount == 0)
+	if (TransamVariables->oidCount == 0)
 	{
-		XLogPutNextOid(ShmemVariableCache->nextOid + VAR_OID_PREFETCH);
-		ShmemVariableCache->oidCount = VAR_OID_PREFETCH;
+		XLogPutNextOid(TransamVariables->nextOid + VAR_OID_PREFETCH);
+		TransamVariables->oidCount = VAR_OID_PREFETCH;
 	}
 
-	result = ShmemVariableCache->nextOid;
+	result = TransamVariables->nextOid;
 
-	(ShmemVariableCache->nextOid)++;
-	(ShmemVariableCache->oidCount)--;
+	(TransamVariables->nextOid)++;
+	(TransamVariables->oidCount)--;
 
 	LWLockRelease(OidGenLock);
 
@@ -629,12 +629,12 @@ SetNextObjectId(Oid nextOid)
 	/* Taking the lock is, therefore, just pro forma; but do it anyway */
 	LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
 
-	if (ShmemVariableCache->nextOid > nextOid)
+	if (TransamVariables->nextOid > nextOid)
 		elog(ERROR, "too late to advance OID counter to %u, it is now %u",
-			 nextOid, ShmemVariableCache->nextOid);
+			 nextOid, TransamVariables->nextOid);
 
-	ShmemVariableCache->nextOid = nextOid;
-	ShmemVariableCache->oidCount = 0;
+	TransamVariables->nextOid = nextOid;
+	TransamVariables->oidCount = 0;
 
 	LWLockRelease(OidGenLock);
 }
@@ -661,7 +661,7 @@ StopGeneratingPinnedObjectIds(void)
  * Assert that xid is between [oldestXid, nextXid], which is the range we
  * expect XIDs coming from tables etc to be in.
  *
- * As ShmemVariableCache->oldestXid could change just after this call without
+ * As TransamVariables->oldestXid could change just after this call without
  * further precautions, and as a wrapped-around xid could again fall within
  * the valid range, this assertion can only detect if something is definitely
  * wrong, but not establish correctness.
@@ -696,8 +696,8 @@ AssertTransactionIdInAllowableRange(TransactionId xid)
 	 * before we see the updated nextXid value.
 	 */
 	pg_memory_barrier();
-	oldest_xid = ShmemVariableCache->oldestXid;
-	next_xid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
+	oldest_xid = TransamVariables->oldestXid;
+	next_xid = XidFromFullTransactionId(TransamVariables->nextXid);
 
 	Assert(TransactionIdFollowsOrEquals(xid, oldest_xid) ||
 		   TransactionIdPrecedesOrEquals(xid, next_xid));

src/backend/access/transam/xlog.c

@@ -4819,9 +4819,9 @@ BootStrapXLOG(void)
 	checkPoint.time = (pg_time_t) time(NULL);
 	checkPoint.oldestActiveXid = InvalidTransactionId;
 
-	ShmemVariableCache->nextXid = checkPoint.nextXid;
-	ShmemVariableCache->nextOid = checkPoint.nextOid;
-	ShmemVariableCache->oidCount = 0;
+	TransamVariables->nextXid = checkPoint.nextXid;
+	TransamVariables->nextOid = checkPoint.nextOid;
+	TransamVariables->oidCount = 0;
 	MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
 	AdvanceOldestClogXid(checkPoint.oldestXid);
 	SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
@@ -5285,9 +5285,9 @@ StartupXLOG(void)
 	checkPoint = ControlFile->checkPointCopy;
 
 	/* initialize shared memory variables from the checkpoint record */
-	ShmemVariableCache->nextXid = checkPoint.nextXid;
-	ShmemVariableCache->nextOid = checkPoint.nextOid;
-	ShmemVariableCache->oidCount = 0;
+	TransamVariables->nextXid = checkPoint.nextXid;
+	TransamVariables->nextOid = checkPoint.nextOid;
+	TransamVariables->oidCount = 0;
 	MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
 	AdvanceOldestClogXid(checkPoint.oldestXid);
 	SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
@@ -5323,7 +5323,7 @@ StartupXLOG(void)
 	StartupReorderBuffer();
 
 	/*
-	 * Startup CLOG. This must be done after ShmemVariableCache->nextXid has
+	 * Startup CLOG. This must be done after TransamVariables->nextXid has
 	 * been initialized and before we accept connections or begin WAL replay.
 	 */
 	StartupCLOG();
@@ -5512,7 +5512,7 @@ StartupXLOG(void)
 			Assert(TransactionIdIsValid(oldestActiveXID));
 
 			/* Tell procarray about the range of xids it has to deal with */
-			ProcArrayInitRecovery(XidFromFullTransactionId(ShmemVariableCache->nextXid));
+			ProcArrayInitRecovery(XidFromFullTransactionId(TransamVariables->nextXid));
 
 			/*
 			 * Startup subtrans only.  CLOG, MultiXact and commit timestamp
@@ -5786,8 +5786,8 @@ StartupXLOG(void)
 
 	/* also initialize latestCompletedXid, to nextXid - 1 */
 	LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
-	ShmemVariableCache->latestCompletedXid = ShmemVariableCache->nextXid;
-	FullTransactionIdRetreat(&ShmemVariableCache->latestCompletedXid);
+	TransamVariables->latestCompletedXid = TransamVariables->nextXid;
+	FullTransactionIdRetreat(&TransamVariables->latestCompletedXid);
 	LWLockRelease(ProcArrayLock);
 
 	/*
@@ -6779,20 +6779,20 @@ CreateCheckPoint(int flags)
 	 * there.
 	 */
 	LWLockAcquire(XidGenLock, LW_SHARED);
-	checkPoint.nextXid = ShmemVariableCache->nextXid;
-	checkPoint.oldestXid = ShmemVariableCache->oldestXid;
-	checkPoint.oldestXidDB = ShmemVariableCache->oldestXidDB;
+	checkPoint.nextXid = TransamVariables->nextXid;
+	checkPoint.oldestXid = TransamVariables->oldestXid;
+	checkPoint.oldestXidDB = TransamVariables->oldestXidDB;
 	LWLockRelease(XidGenLock);
 
 	LWLockAcquire(CommitTsLock, LW_SHARED);
-	checkPoint.oldestCommitTsXid = ShmemVariableCache->oldestCommitTsXid;
-	checkPoint.newestCommitTsXid = ShmemVariableCache->newestCommitTsXid;
+	checkPoint.oldestCommitTsXid = TransamVariables->oldestCommitTsXid;
+	checkPoint.newestCommitTsXid = TransamVariables->newestCommitTsXid;
 	LWLockRelease(CommitTsLock);
 
 	LWLockAcquire(OidGenLock, LW_SHARED);
-	checkPoint.nextOid = ShmemVariableCache->nextOid;
+	checkPoint.nextOid = TransamVariables->nextOid;
 	if (!shutdown)
-		checkPoint.nextOid += ShmemVariableCache->oidCount;
+		checkPoint.nextOid += TransamVariables->oidCount;
 	LWLockRelease(OidGenLock);
 
 	MultiXactGetCheckptMulti(shutdown,
@@ -7884,16 +7884,16 @@ xlog_redo(XLogReaderState *record)
 		Oid			nextOid;
 
 		/*
-		 * We used to try to take the maximum of ShmemVariableCache->nextOid
-		 * and the recorded nextOid, but that fails if the OID counter wraps
+		 * We used to try to take the maximum of TransamVariables->nextOid and
+		 * the recorded nextOid, but that fails if the OID counter wraps
 		 * around.  Since no OID allocation should be happening during replay
 		 * anyway, better to just believe the record exactly.  We still take
 		 * OidGenLock while setting the variable, just in case.
 		 */
 		memcpy(&nextOid, XLogRecGetData(record), sizeof(Oid));
 		LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
-		ShmemVariableCache->nextOid = nextOid;
-		ShmemVariableCache->oidCount = 0;
+		TransamVariables->nextOid = nextOid;
+		TransamVariables->oidCount = 0;
 		LWLockRelease(OidGenLock);
 	}
 	else if (info == XLOG_CHECKPOINT_SHUTDOWN)
@@ -7904,11 +7904,11 @@ xlog_redo(XLogReaderState *record)
 		memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
 		/* In a SHUTDOWN checkpoint, believe the counters exactly */
 		LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
-		ShmemVariableCache->nextXid = checkPoint.nextXid;
+		TransamVariables->nextXid = checkPoint.nextXid;
 		LWLockRelease(XidGenLock);
 		LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
-		ShmemVariableCache->nextOid = checkPoint.nextOid;
-		ShmemVariableCache->oidCount = 0;
+		TransamVariables->nextOid = checkPoint.nextOid;
+		TransamVariables->oidCount = 0;
 		LWLockRelease(OidGenLock);
 		MultiXactSetNextMXact(checkPoint.nextMulti,
 							  checkPoint.nextMultiOffset);
@@ -8001,9 +8001,9 @@ xlog_redo(XLogReaderState *record)
 		memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
 		/* In an ONLINE checkpoint, treat the XID counter as a minimum */
 		LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
-		if (FullTransactionIdPrecedes(ShmemVariableCache->nextXid,
+		if (FullTransactionIdPrecedes(TransamVariables->nextXid,
 									  checkPoint.nextXid))
-			ShmemVariableCache->nextXid = checkPoint.nextXid;
+			TransamVariables->nextXid = checkPoint.nextXid;
 		LWLockRelease(XidGenLock);
 
 		/*
@@ -8028,7 +8028,7 @@ xlog_redo(XLogReaderState *record)
 		 */
 		MultiXactAdvanceOldest(checkPoint.oldestMulti,
 							   checkPoint.oldestMultiDB);
-		if (TransactionIdPrecedes(ShmemVariableCache->oldestXid,
+		if (TransactionIdPrecedes(TransamVariables->oldestXid,
 								  checkPoint.oldestXid))
 			SetTransactionIdLimit(checkPoint.oldestXid,
 								  checkPoint.oldestXidDB);

src/backend/access/transam/xlogreader.c

@@ -2182,8 +2182,8 @@ XLogRecGetFullXid(XLogReaderState *record)
 	Assert(AmStartupProcess() || !IsUnderPostmaster);
 
 	xid = XLogRecGetXid(record);
-	next_xid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
-	epoch = EpochFromFullTransactionId(ShmemVariableCache->nextXid);
+	next_xid = XidFromFullTransactionId(TransamVariables->nextXid);
+	epoch = EpochFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
 	 * If xid is numerically greater than next_xid, it has to be from the last

src/backend/access/transam/xlogrecovery.c

@@ -1869,7 +1869,7 @@ ApplyWalRecord(XLogReaderState *xlogreader, XLogRecord *record, TimeLineID *repl
 	error_context_stack = &errcallback;
 
 	/*
-	 * ShmemVariableCache->nextXid must be beyond record's xid.
+	 * TransamVariables->nextXid must be beyond record's xid.
 	 */
 	AdvanceNextFullTransactionIdPastXid(record->xl_xid);