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/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 XactCompletionForceSyncCommit(xlrec)		((xlrec)->xinfo & XACT_COMPLETION_FORCE_SYNC_COMMIT)
+#define XactCompletionRelcacheInitFileInval(xinfo)	(xinfo & XACT_COMPLETION_UPDATE_RELCACHE_FILE)
+#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
 {