Replace literal 0 with InvalidXLogRecPtr for XLogRecPtr assignments

Use the proper constant InvalidXLogRecPtr instead of literal 0 when
assigning XLogRecPtr variables and struct fields.

This improves code clarity by making it explicit that these are
invalid LSN values rather than ambiguous zero literals.

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/aRtd2dw8FO1nNX7k@ip-10-97-1-34.eu-west-3.compute.internal

src/backend/access/gist/gist.c

@@ -291,7 +291,7 @@ gistplacetopage(Relation rel, Size freespace, GISTSTATE *giststate,
 		SplitPageLayout *dist = NULL,
 				   *ptr;
 		BlockNumber oldrlink = InvalidBlockNumber;
-		GistNSN		oldnsn = 0;
+		GistNSN		oldnsn = InvalidXLogRecPtr;
 		SplitPageLayout rootpg;
 		bool		is_rootsplit;
 		int			npage;
@@ -654,7 +654,7 @@ gistdoinsert(Relation r, IndexTuple itup, Size freespace,
 
 	/* Start from the root */
 	firststack.blkno = GIST_ROOT_BLKNO;
-	firststack.lsn = 0;
+	firststack.lsn = InvalidXLogRecPtr;
 	firststack.retry_from_parent = false;
 	firststack.parent = NULL;
 	firststack.downlinkoffnum = InvalidOffsetNumber;

src/backend/access/transam/parallel.c

@@ -357,7 +357,7 @@ InitializeParallelDSM(ParallelContext *pcxt)
 	fps->stmt_ts = GetCurrentStatementStartTimestamp();
 	fps->serializable_xact_handle = ShareSerializableXact();
 	SpinLockInit(&fps->mutex);
-	fps->last_xlog_end = 0;
+	fps->last_xlog_end = InvalidXLogRecPtr;
 	shm_toc_insert(pcxt->toc, PARALLEL_KEY_FIXED, fps);
 
 	/* We can skip the rest of this if we're not budgeting for any workers. */
@@ -530,7 +530,7 @@ ReinitializeParallelDSM(ParallelContext *pcxt)
 
 	/* Reset a few bits of fixed parallel state to a clean state. */
 	fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED, false);
-	fps->last_xlog_end = 0;
+	fps->last_xlog_end = InvalidXLogRecPtr;
 
 	/* Recreate error queues (if they exist). */
 	if (pcxt->nworkers > 0)

src/backend/access/transam/xlog.c

@@ -2060,7 +2060,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli, bool opportunistic)
 					/* Have to write it ourselves */
 					TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_START();
 					WriteRqst.Write = OldPageRqstPtr;
-					WriteRqst.Flush = 0;
+					WriteRqst.Flush = InvalidXLogRecPtr;
 					XLogWrite(WriteRqst, tli, false);
 					LWLockRelease(WALWriteLock);
 					pgWalUsage.wal_buffers_full++;
@@ -3077,7 +3077,7 @@ XLogBackgroundFlush(void)
 	else
 	{
 		/* no flushing, this time round */
-		WriteRqst.Flush = 0;
+		WriteRqst.Flush = InvalidXLogRecPtr;
 	}
 
 #ifdef WAL_DEBUG
@@ -5207,7 +5207,7 @@ BootStrapXLOG(uint32 data_checksum_version)
 	/* Insert the initial checkpoint record */
 	recptr = ((char *) page + SizeOfXLogLongPHD);
 	record = (XLogRecord *) recptr;
-	record->xl_prev = 0;
+	record->xl_prev = InvalidXLogRecPtr;
 	record->xl_xid = InvalidTransactionId;
 	record->xl_tot_len = SizeOfXLogRecord + SizeOfXLogRecordDataHeaderShort + sizeof(checkPoint);
 	record->xl_info = XLOG_CHECKPOINT_SHUTDOWN;

src/backend/access/transam/xlogprefetcher.c

@@ -967,7 +967,7 @@ XLogPrefetcherBeginRead(XLogPrefetcher *prefetcher, XLogRecPtr recPtr)
 	/* Book-keeping to avoid readahead on first read. */
 	prefetcher->begin_ptr = recPtr;
 
-	prefetcher->no_readahead_until = 0;
+	prefetcher->no_readahead_until = InvalidXLogRecPtr;
 
 	/* This will forget about any queued up records in the decoder. */
 	XLogBeginRead(prefetcher->reader, recPtr);

src/backend/access/transam/xlogrecovery.c

@@ -261,7 +261,7 @@ static TimestampTz XLogReceiptTime = 0;
 static XLogSource XLogReceiptSource = XLOG_FROM_ANY;
 
 /* Local copy of WalRcv->flushedUpto */
-static XLogRecPtr flushedUpto = 0;
+static XLogRecPtr flushedUpto = InvalidXLogRecPtr;
 static TimeLineID receiveTLI = 0;
 
 /*
@@ -3918,7 +3918,7 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
 						RequestXLogStreaming(tli, ptr, PrimaryConnInfo,
 											 PrimarySlotName,
 											 wal_receiver_create_temp_slot);
-						flushedUpto = 0;
+						flushedUpto = InvalidXLogRecPtr;
 					}
 
 					/*
@@ -4096,7 +4096,7 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
 static int
 emode_for_corrupt_record(int emode, XLogRecPtr RecPtr)
 {
-	static XLogRecPtr lastComplaint = 0;
+	static XLogRecPtr lastComplaint = InvalidXLogRecPtr;
 
 	if (readSource == XLOG_FROM_PG_WAL && emode == LOG)
 	{

src/backend/replication/syncrep.c

@@ -355,7 +355,7 @@ SyncRepWaitForLSN(XLogRecPtr lsn, bool commit)
 	pg_read_barrier();
 	Assert(dlist_node_is_detached(&MyProc->syncRepLinks));
 	MyProc->syncRepState = SYNC_REP_NOT_WAITING;
-	MyProc->waitLSN = 0;
+	MyProc->waitLSN = InvalidXLogRecPtr;
 
 	/* reset ps display to remove the suffix */
 	if (update_process_title)
@@ -1027,7 +1027,7 @@ SyncRepQueueIsOrderedByLSN(int mode)
 
 	Assert(mode >= 0 && mode < NUM_SYNC_REP_WAIT_MODE);
 
-	lastLSN = 0;
+	lastLSN = InvalidXLogRecPtr;
 
 	dlist_foreach(iter, &WalSndCtl->SyncRepQueue[mode])
 	{

src/backend/replication/walreceiver.c

@@ -1122,8 +1122,8 @@ XLogWalRcvClose(XLogRecPtr recptr, TimeLineID tli)
 static void
 XLogWalRcvSendReply(bool force, bool requestReply)
 {
-	static XLogRecPtr writePtr = 0;
-	static XLogRecPtr flushPtr = 0;
+	static XLogRecPtr writePtr = InvalidXLogRecPtr;
+	static XLogRecPtr flushPtr = InvalidXLogRecPtr;
 	XLogRecPtr	applyPtr;
 	TimestampTz now;
 

src/backend/storage/lmgr/proc.c

@@ -509,7 +509,7 @@ InitProcess(void)
 	MyProc->recoveryConflictPending = false;
 
 	/* Initialize fields for sync rep */
-	MyProc->waitLSN = 0;
+	MyProc->waitLSN = InvalidXLogRecPtr;
 	MyProc->syncRepState = SYNC_REP_NOT_WAITING;
 	dlist_node_init(&MyProc->syncRepLinks);
 

src/bin/pg_resetwal/pg_resetwal.c

@@ -913,10 +913,10 @@ RewriteControlFile(void)
 
 	ControlFile.state = DB_SHUTDOWNED;
 	ControlFile.checkPoint = ControlFile.checkPointCopy.redo;
-	ControlFile.minRecoveryPoint = 0;
+	ControlFile.minRecoveryPoint = InvalidXLogRecPtr;
 	ControlFile.minRecoveryPointTLI = 0;
-	ControlFile.backupStartPoint = 0;
-	ControlFile.backupEndPoint = 0;
+	ControlFile.backupStartPoint = InvalidXLogRecPtr;
+	ControlFile.backupEndPoint = InvalidXLogRecPtr;
 	ControlFile.backupEndRequired = false;
 
 	/*
@@ -1147,7 +1147,7 @@ WriteEmptyXLOG(void)
 	/* Insert the initial checkpoint record */
 	recptr = (char *) page + SizeOfXLogLongPHD;
 	record = (XLogRecord *) recptr;
-	record->xl_prev = 0;
+	record->xl_prev = InvalidXLogRecPtr;
 	record->xl_xid = InvalidTransactionId;
 	record->xl_tot_len = SizeOfXLogRecord + SizeOfXLogRecordDataHeaderShort + sizeof(CheckPoint);
 	record->xl_info = XLOG_CHECKPOINT_SHUTDOWN;

src/bin/pg_rewind/pg_rewind.c

@@ -377,7 +377,7 @@ main(int argc, char **argv)
 	{
 		pg_log_info("source and target cluster are on the same timeline");
 		rewind_needed = false;
-		target_wal_endrec = 0;
+		target_wal_endrec = InvalidXLogRecPtr;
 	}
 	else
 	{