Introduce compact WAL record for the common case of commit (non-DDL).

XLOG_XACT_COMMIT_COMPACT leaves out invalidation messages and relfilenodes,
saving considerable space for the vast majority of transaction commits.
XLOG_XACT_COMMIT keeps same definition as XLOG_PAGE_MAGIC 0xD067 and earlier.

Leonardo Francalanci and Simon Riggs

src/backend/access/transam/xact.c

@@ -962,25 +962,9 @@ RecordTransactionCommit(void)
 		/*
 		 * Begin commit critical section and insert the commit XLOG record.
 		 */
-		XLogRecData rdata[4];
-		int			lastrdata = 0;
-		xl_xact_commit xlrec;
-
 		/* Tell bufmgr and smgr to prepare for commit */
 		BufmgrCommit();
 
-		/*
-		 * Set flags required for recovery processing of commits.
-		 */
-		xlrec.xinfo = 0;
-		if (RelcacheInitFileInval)
-			xlrec.xinfo |= XACT_COMPLETION_UPDATE_RELCACHE_FILE;
-		if (forceSyncCommit)
-			xlrec.xinfo |= XACT_COMPLETION_FORCE_SYNC_COMMIT;
-
-		xlrec.dbId = MyDatabaseId;
-		xlrec.tsId = MyDatabaseTableSpace;
-
 		/*
 		 * Mark ourselves as within our "commit critical section".	This
 		 * forces any concurrent checkpoint to wait until we've updated
@@ -1002,43 +986,88 @@ RecordTransactionCommit(void)
 		MyProc->inCommit = true;
 
 		SetCurrentTransactionStopTimestamp();
-		xlrec.xact_time = xactStopTimestamp;
-		xlrec.nrels = nrels;
-		xlrec.nsubxacts = nchildren;
-		xlrec.nmsgs = nmsgs;
-		rdata[0].data = (char *) (&xlrec);
-		rdata[0].len = MinSizeOfXactCommit;
-		rdata[0].buffer = InvalidBuffer;
-		/* dump rels to delete */
-		if (nrels > 0)
-		{
-			rdata[0].next = &(rdata[1]);
-			rdata[1].data = (char *) rels;
-			rdata[1].len = nrels * sizeof(RelFileNode);
-			rdata[1].buffer = InvalidBuffer;
-			lastrdata = 1;
-		}
-		/* dump committed child Xids */
-		if (nchildren > 0)
-		{
-			rdata[lastrdata].next = &(rdata[2]);
-			rdata[2].data = (char *) children;
-			rdata[2].len = nchildren * sizeof(TransactionId);
-			rdata[2].buffer = InvalidBuffer;
-			lastrdata = 2;
-		}
-		/* dump shared cache invalidation messages */
-		if (nmsgs > 0)
-		{
-			rdata[lastrdata].next = &(rdata[3]);
-			rdata[3].data = (char *) invalMessages;
-			rdata[3].len = nmsgs * sizeof(SharedInvalidationMessage);
-			rdata[3].buffer = InvalidBuffer;
-			lastrdata = 3;
-		}
-		rdata[lastrdata].next = NULL;
 
-		(void) XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT, rdata);
+		/*
+		 * Do we need the long commit record? If not, use the compact format.
+		 */
+		if (nrels > 0 || nmsgs > 0 || RelcacheInitFileInval || forceSyncCommit)
+		{
+			XLogRecData rdata[4];
+			int			lastrdata = 0;
+			xl_xact_commit xlrec;
+			/*
+			 * Set flags required for recovery processing of commits.
+			 */
+			xlrec.xinfo = 0;
+			if (RelcacheInitFileInval)
+				xlrec.xinfo |= XACT_COMPLETION_UPDATE_RELCACHE_FILE;
+			if (forceSyncCommit)
+				xlrec.xinfo |= XACT_COMPLETION_FORCE_SYNC_COMMIT;
+
+			xlrec.dbId = MyDatabaseId;
+			xlrec.tsId = MyDatabaseTableSpace;
+
+			xlrec.xact_time = xactStopTimestamp;
+			xlrec.nrels = nrels;
+			xlrec.nsubxacts = nchildren;
+			xlrec.nmsgs = nmsgs;
+			rdata[0].data = (char *) (&xlrec);
+			rdata[0].len = MinSizeOfXactCommit;
+			rdata[0].buffer = InvalidBuffer;
+			/* dump rels to delete */
+			if (nrels > 0)
+			{
+				rdata[0].next = &(rdata[1]);
+				rdata[1].data = (char *) rels;
+				rdata[1].len = nrels * sizeof(RelFileNode);
+				rdata[1].buffer = InvalidBuffer;
+				lastrdata = 1;
+			}
+			/* dump committed child Xids */
+			if (nchildren > 0)
+			{
+				rdata[lastrdata].next = &(rdata[2]);
+				rdata[2].data = (char *) children;
+				rdata[2].len = nchildren * sizeof(TransactionId);
+				rdata[2].buffer = InvalidBuffer;
+				lastrdata = 2;
+			}
+			/* dump shared cache invalidation messages */
+			if (nmsgs > 0)
+			{
+				rdata[lastrdata].next = &(rdata[3]);
+				rdata[3].data = (char *) invalMessages;
+				rdata[3].len = nmsgs * sizeof(SharedInvalidationMessage);
+				rdata[3].buffer = InvalidBuffer;
+				lastrdata = 3;
+			}
+			rdata[lastrdata].next = NULL;
+
+			(void) XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT, rdata);
+		}
+		else
+		{
+			XLogRecData rdata[2];
+			int			lastrdata = 0;
+			xl_xact_commit_compact	xlrec;
+			xlrec.xact_time = xactStopTimestamp;
+			xlrec.nsubxacts = nchildren;
+			rdata[0].data = (char *) (&xlrec);
+			rdata[0].len = MinSizeOfXactCommitCompact;
+			rdata[0].buffer = InvalidBuffer;
+			/* dump committed child Xids */
+			if (nchildren > 0)
+			{
+				rdata[0].next = &(rdata[1]);
+				rdata[1].data = (char *) children;
+				rdata[1].len = nchildren * sizeof(TransactionId);
+				rdata[1].buffer = InvalidBuffer;
+				lastrdata = 1;
+			}
+			rdata[lastrdata].next = NULL;
+
+			(void) XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT_COMPACT, rdata);
+		}
 	}
 
 	/*
@@ -4441,19 +4470,17 @@ xactGetCommittedChildren(TransactionId **ptr)
  * actions for which the order of execution is critical.
  */
 static void
-xact_redo_commit(xl_xact_commit *xlrec, TransactionId xid, XLogRecPtr lsn)
+xact_redo_commit_internal(TransactionId xid, XLogRecPtr lsn,
+					TransactionId *sub_xids, int nsubxacts,
+					SharedInvalidationMessage *inval_msgs, int nmsgs,
+					RelFileNode *xnodes, int nrels,
+					Oid dbId, Oid tsId,
+					uint32 xinfo)
 {
-	TransactionId *sub_xids;
-	SharedInvalidationMessage *inval_msgs;
 	TransactionId max_xid;
 	int			i;
 
-	/* subxid array follows relfilenodes */
+	max_xid = TransactionIdLatest(xid, nsubxacts, sub_xids);
-	sub_xids = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
-	/* invalidation messages array follows subxids */
-	inval_msgs = (SharedInvalidationMessage *) &(sub_xids[xlrec->nsubxacts]);
-
-	max_xid = TransactionIdLatest(xid, xlrec->nsubxacts, sub_xids);
 
 	/*
 	 * Make sure nextXid is beyond any XID mentioned in the record.
@@ -4476,7 +4503,7 @@ xact_redo_commit(xl_xact_commit *xlrec, TransactionId xid, XLogRecPtr lsn)
 		/*
 		 * Mark the transaction committed in pg_clog.
 		 */
-		TransactionIdCommitTree(xid, xlrec->nsubxacts, sub_xids);
+		TransactionIdCommitTree(xid, nsubxacts, sub_xids);
 	}
 	else
 	{
@@ -4500,41 +4527,41 @@ xact_redo_commit(xl_xact_commit *xlrec, TransactionId xid, XLogRecPtr lsn)
 		 * bits set on changes made by transactions that haven't yet
 		 * recovered. It's unlikely but it's good to be safe.
 		 */
-		TransactionIdAsyncCommitTree(xid, xlrec->nsubxacts, sub_xids, lsn);
+		TransactionIdAsyncCommitTree(xid, nsubxacts, sub_xids, lsn);
 
 		/*
 		 * We must mark clog before we update the ProcArray.
 		 */
-		ExpireTreeKnownAssignedTransactionIds(xid, xlrec->nsubxacts, sub_xids, max_xid);
+		ExpireTreeKnownAssignedTransactionIds(xid, nsubxacts, sub_xids, max_xid);
 
 		/*
 		 * Send any cache invalidations attached to the commit. We must
 		 * maintain the same order of invalidation then release locks as
 		 * occurs in CommitTransaction().
 		 */
-		ProcessCommittedInvalidationMessages(inval_msgs, xlrec->nmsgs,
+		ProcessCommittedInvalidationMessages(inval_msgs, nmsgs,
-								  XactCompletionRelcacheInitFileInval(xlrec),
+								  XactCompletionRelcacheInitFileInval(xinfo),
-											 xlrec->dbId, xlrec->tsId);
+											 dbId, tsId);
 
 		/*
 		 * Release locks, if any. We do this for both two phase and normal one
 		 * phase transactions. In effect we are ignoring the prepare phase and
 		 * just going straight to lock release.
 		 */
-		StandbyReleaseLockTree(xid, xlrec->nsubxacts, sub_xids);
+		StandbyReleaseLockTree(xid, nsubxacts, sub_xids);
 	}
 
 	/* Make sure files supposed to be dropped are dropped */
-	for (i = 0; i < xlrec->nrels; i++)
+	for (i = 0; i < nrels; i++)
 	{
-		SMgrRelation srel = smgropen(xlrec->xnodes[i], InvalidBackendId);
+		SMgrRelation srel = smgropen(xnodes[i], InvalidBackendId);
 		ForkNumber	fork;
 
 		for (fork = 0; fork <= MAX_FORKNUM; fork++)
 		{
 			if (smgrexists(srel, fork))
 			{
-				XLogDropRelation(xlrec->xnodes[i], fork);
+				XLogDropRelation(xnodes[i], fork);
 				smgrdounlink(srel, fork, true);
 			}
 		}
@@ -4553,8 +4580,46 @@ xact_redo_commit(xl_xact_commit *xlrec, TransactionId xid, XLogRecPtr lsn)
 	 * to reduce that problem window, for any user that requested
 	 * ForceSyncCommit().
 	 */
-	if (XactCompletionForceSyncCommit(xlrec))
+	if (XactCompletionForceSyncCommit(xinfo))
 		XLogFlush(lsn);
+
+}
+/*
+ * Utility function to call xact_redo_commit_internal after breaking down xlrec
+ */
+static void
+xact_redo_commit(xl_xact_commit *xlrec,
+							TransactionId xid, XLogRecPtr lsn)
+{
+	TransactionId *subxacts;
+	SharedInvalidationMessage *inval_msgs;
+
+	/* subxid array follows relfilenodes */
+	subxacts = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
+	/* invalidation messages array follows subxids */
+	inval_msgs = (SharedInvalidationMessage *) &(subxacts[xlrec->nsubxacts]);
+
+	xact_redo_commit_internal(xid, lsn, subxacts, xlrec->nsubxacts,
+								inval_msgs, xlrec->nmsgs,
+								xlrec->xnodes, xlrec->nrels,
+								xlrec->dbId,
+								xlrec->tsId,
+								xlrec->xinfo);
+}
+
+/*
+ * Utility function to call xact_redo_commit_internal  for compact form of message.
+ */
+static void
+xact_redo_commit_compact(xl_xact_commit_compact *xlrec,
+							TransactionId xid, XLogRecPtr lsn)
+{
+	xact_redo_commit_internal(xid, lsn, xlrec->subxacts, xlrec->nsubxacts,
+								NULL, 0,		/* inval msgs */
+								NULL, 0,		/* relfilenodes */
+								InvalidOid,		/* dbId */
+								InvalidOid,		/* tsId */
+								0);				/* xinfo */
 }
 
 /*
@@ -4655,7 +4720,13 @@ xact_redo(XLogRecPtr lsn, XLogRecord *record)
 	/* Backup blocks are not used in xact records */
 	Assert(!(record->xl_info & XLR_BKP_BLOCK_MASK));
 
-	if (info == XLOG_XACT_COMMIT)
+	if (info == XLOG_XACT_COMMIT_COMPACT)
+	{
+		xl_xact_commit_compact *xlrec = (xl_xact_commit_compact *) XLogRecGetData(record);
+
+		xact_redo_commit_compact(xlrec, record->xl_xid, lsn);
+	}
+	else if (info == XLOG_XACT_COMMIT)
 	{
 		xl_xact_commit *xlrec = (xl_xact_commit *) XLogRecGetData(record);
 
@@ -4703,9 +4774,9 @@ static void
 xact_desc_commit(StringInfo buf, xl_xact_commit *xlrec)
 {
 	int			i;
-	TransactionId *xacts;
+	TransactionId *subxacts;
 
-	xacts = (TransactionId *) &xlrec->xnodes[xlrec->nrels];
+	subxacts = (TransactionId *) &xlrec->xnodes[xlrec->nrels];
 
 	appendStringInfoString(buf, timestamptz_to_str(xlrec->xact_time));
 
@@ -4724,15 +4795,15 @@ xact_desc_commit(StringInfo buf, xl_xact_commit *xlrec)
 	{
 		appendStringInfo(buf, "; subxacts:");
 		for (i = 0; i < xlrec->nsubxacts; i++)
-			appendStringInfo(buf, " %u", xacts[i]);
+			appendStringInfo(buf, " %u", subxacts[i]);
 	}
 	if (xlrec->nmsgs > 0)
 	{
 		SharedInvalidationMessage *msgs;
 
-		msgs = (SharedInvalidationMessage *) &xacts[xlrec->nsubxacts];
+		msgs = (SharedInvalidationMessage *) &subxacts[xlrec->nsubxacts];
 
-		if (XactCompletionRelcacheInitFileInval(xlrec))
+		if (XactCompletionRelcacheInitFileInval(xlrec->xinfo))
 			appendStringInfo(buf, "; relcache init file inval dbid %u tsid %u",
 							 xlrec->dbId, xlrec->tsId);
 
@@ -4758,6 +4829,21 @@ xact_desc_commit(StringInfo buf, xl_xact_commit *xlrec)
 	}
 }
 
+static void
+xact_desc_commit_compact(StringInfo buf, xl_xact_commit_compact *xlrec)
+{
+	int			i;
+
+	appendStringInfoString(buf, timestamptz_to_str(xlrec->xact_time));
+
+	if (xlrec->nsubxacts > 0)
+	{
+		appendStringInfo(buf, "; subxacts:");
+		for (i = 0; i < xlrec->nsubxacts; i++)
+			appendStringInfo(buf, " %u", xlrec->subxacts[i]);
+	}
+}
+
 static void
 xact_desc_abort(StringInfo buf, xl_xact_abort *xlrec)
 {
@@ -4802,7 +4888,14 @@ xact_desc(StringInfo buf, uint8 xl_info, char *rec)
 {
 	uint8		info = xl_info & ~XLR_INFO_MASK;
 
-	if (info == XLOG_XACT_COMMIT)
+	if (info == XLOG_XACT_COMMIT_COMPACT)
+	{
+		xl_xact_commit_compact *xlrec = (xl_xact_commit_compact *) rec;
+
+		appendStringInfo(buf, "commit: ");
+		xact_desc_commit_compact(buf, xlrec);
+	}
+	else if (info == XLOG_XACT_COMMIT)
 	{
 		xl_xact_commit *xlrec = (xl_xact_commit *) rec;
 

src/backend/access/transam/xlog.c

@@ -5593,7 +5593,14 @@ recoveryStopsHere(XLogRecord *record, bool *includeThis)
 	if (record->xl_rmid != RM_XACT_ID && record->xl_rmid != RM_XLOG_ID)
 		return false;
 	record_info = record->xl_info & ~XLR_INFO_MASK;
-	if (record->xl_rmid == RM_XACT_ID && record_info == XLOG_XACT_COMMIT)
+	if (record->xl_rmid == RM_XACT_ID && record_info == XLOG_XACT_COMMIT_COMPACT)
+	{
+		xl_xact_commit_compact *recordXactCommitData;
+
+		recordXactCommitData = (xl_xact_commit_compact *) XLogRecGetData(record);
+		recordXtime = recordXactCommitData->xact_time;
+	}
+	else if (record->xl_rmid == RM_XACT_ID && record_info == XLOG_XACT_COMMIT)
 	{
 		xl_xact_commit *recordXactCommitData;
 
@@ -5680,7 +5687,7 @@ recoveryStopsHere(XLogRecord *record, bool *includeThis)
 		recoveryStopTime = recordXtime;
 		recoveryStopAfter = *includeThis;
 
-		if (record_info == XLOG_XACT_COMMIT)
+		if (record_info == XLOG_XACT_COMMIT_COMPACT || record_info == XLOG_XACT_COMMIT)
 		{
 			if (recoveryStopAfter)
 				ereport(LOG,

src/include/access/xact.h

@@ -106,6 +106,7 @@ typedef void (*SubXactCallback) (SubXactEvent event, SubTransactionId mySubid,
 #define XLOG_XACT_COMMIT_PREPARED	0x30
 #define XLOG_XACT_ABORT_PREPARED	0x40
 #define XLOG_XACT_ASSIGNMENT		0x50
+#define XLOG_XACT_COMMIT_COMPACT	0x60
 
 typedef struct xl_xact_assignment
 {
@@ -116,6 +117,16 @@ typedef struct xl_xact_assignment
 
 #define MinSizeOfXactAssignment offsetof(xl_xact_assignment, xsub)
 
+typedef struct xl_xact_commit_compact
+{
+	TimestampTz xact_time;		/* time of commit */
+	int			nsubxacts;		/* number of subtransaction XIDs */
+	/* ARRAY OF COMMITTED SUBTRANSACTION XIDs FOLLOWS */
+	TransactionId subxacts[1];	/* VARIABLE LENGTH ARRAY */
+} xl_xact_commit_compact;
+
+#define MinSizeOfXactCommitCompact offsetof(xl_xact_commit_compact, subxacts)
+
 typedef struct xl_xact_commit
 {
 	TimestampTz xact_time;		/* time of commit */
@@ -145,8 +156,8 @@ typedef struct xl_xact_commit
 #define XACT_COMPLETION_FORCE_SYNC_COMMIT		0x02
 
 /* Access macros for above flags */
-#define XactCompletionRelcacheInitFileInval(xlrec)	((xlrec)->xinfo & XACT_COMPLETION_UPDATE_RELCACHE_FILE)
+#define XactCompletionRelcacheInitFileInval(xinfo)	(xinfo & XACT_COMPLETION_UPDATE_RELCACHE_FILE)
-#define XactCompletionForceSyncCommit(xlrec)		((xlrec)->xinfo & XACT_COMPLETION_FORCE_SYNC_COMMIT)
+#define XactCompletionForceSyncCommit(xinfo)		(xinfo & XACT_COMPLETION_FORCE_SYNC_COMMIT)
 
 typedef struct xl_xact_abort
 {

src/include/access/xlog_internal.h

@@ -71,7 +71,7 @@ typedef struct XLogContRecord
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD067	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD068	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {