Remove all use of ThisTimeLineID global variable outside of xlog.c

All such code deals with this global variable in one of three ways.
Sometimes the same functions use it in more than one of these ways
at the same time.

First, sometimes it's an implicit argument to one or more functions
being called in xlog.c or elsewhere, and must be set to the
appropriate value before calling those functions lest they
misbehave. In those cases, it is now passed as an explicit argument
instead.

Second, sometimes it's used to obtain the current timeline after
the end of recovery, i.e. the timeline to which WAL is being
written and flushed. Such code now calls GetWALInsertionTimeLine()
or relies on the new out parameter added to GetFlushRecPtr().

Third, sometimes it's used during recovery to store the current
replay timeline. That can change, so such code must generally
update the value before each use. It can still do that, but must
now use a local variable instead.

The net effect of these changes is to reduce by a fair amount the
amount of code that is directly accessing this global variable.
That's good, because history has shown that we don't always think
clearly about which timeline ID it's supposed to contain at any
given point in time, or indeed, whether it has been or needs to
be initialized at any given point in the code.

Patch by me, reviewed and tested by Michael Paquier, Amul Sul, and
Álvaro Herrera.

Discussion: https://postgr.es/m/CA+TgmobfAAqhfWa1kaFBBFvX+5CjM=7TE=n4r4Q1o2bjbGYBpA@mail.gmail.com

Author: robertmhaas

src/backend/access/transam/twophase.c

@@ -1373,19 +1373,14 @@ ReadTwoPhaseFile(TransactionId xid, bool missing_ok)
  * twophase files and ReadTwoPhaseFile should be used instead.
  *
  * Note clearly that this function can access WAL during normal operation,
- * similarly to the way WALSender or Logical Decoding would do.  While
- * accessing WAL, read_local_xlog_page() may change ThisTimeLineID,
- * particularly if this routine is called for the end-of-recovery checkpoint
- * in the checkpointer itself, so save the current timeline number value
- * and restore it once done.
+ * similarly to the way WALSender or Logical Decoding would do.
  */
 static void
 XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
 {
 	XLogRecord *record;
 	XLogReaderState *xlogreader;
 	char	   *errormsg;
-	TimeLineID	save_currtli = ThisTimeLineID;
 
 	xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
 									XL_ROUTINE(.page_read = &read_local_xlog_page,
@@ -1401,13 +1396,6 @@ XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
 	XLogBeginRead(xlogreader, lsn);
 	record = XLogReadRecord(xlogreader, &errormsg);
 
-	/*
-	 * Restore immediately the timeline where it was previously, as
-	 * read_local_xlog_page() could have changed it if the record was read
-	 * while recovery was finishing or if the timeline has jumped in-between.
-	 */
-	ThisTimeLineID = save_currtli;
-
 	if (record == NULL)
 		ereport(ERROR,
 				(errcode_for_file_access(),

src/backend/access/transam/xlog.c

@@ -192,7 +192,7 @@ CheckpointStatsData CheckpointStats;
  * ThisTimeLineID will be same in all backends --- it identifies current
  * WAL timeline for the database system.
  */
-TimeLineID	ThisTimeLineID = 0;
+static TimeLineID	ThisTimeLineID = 0;
 
 static XLogRecPtr LastRec;
 
@@ -917,7 +917,8 @@ static void AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic);
 static bool XLogCheckpointNeeded(XLogSegNo new_segno);
 static void XLogWrite(XLogwrtRqst WriteRqst, bool flexible);
 static bool InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
-								   bool find_free, XLogSegNo max_segno);
+								   bool find_free, XLogSegNo max_segno,
+								   TimeLineID tli);
 static int	XLogFileRead(XLogSegNo segno, int emode, TimeLineID tli,
 						 XLogSource source, bool notfoundOk);
 static int	XLogFileReadAnyTLI(XLogSegNo segno, int emode, XLogSource source);
@@ -2518,7 +2519,7 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
 							wal_segment_size);
 
 			/* create/use new log file */
-			openLogFile = XLogFileInit(openLogSegNo);
+			openLogFile = XLogFileInit(openLogSegNo, ThisTimeLineID);
 			ReserveExternalFD();
 		}
 
@@ -2633,15 +2634,15 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
 			 */
 			if (finishing_seg)
 			{
-				issue_xlog_fsync(openLogFile, openLogSegNo);
+				issue_xlog_fsync(openLogFile, openLogSegNo, ThisTimeLineID);
 
 				/* signal that we need to wakeup walsenders later */
 				WalSndWakeupRequest();
 
 				LogwrtResult.Flush = LogwrtResult.Write;	/* end of page */
 
 				if (XLogArchivingActive())
-					XLogArchiveNotifySeg(openLogSegNo);
+					XLogArchiveNotifySeg(openLogSegNo, ThisTimeLineID);
 
 				XLogCtl->lastSegSwitchTime = (pg_time_t) time(NULL);
 				XLogCtl->lastSegSwitchLSN = LogwrtResult.Flush;
@@ -2704,7 +2705,7 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
 				ReserveExternalFD();
 			}
 
-			issue_xlog_fsync(openLogFile, openLogSegNo);
+			issue_xlog_fsync(openLogFile, openLogSegNo, ThisTimeLineID);
 		}
 
 		/* signal that we need to wakeup walsenders later */
@@ -3296,7 +3297,8 @@ XLogNeedsFlush(XLogRecPtr record)
  * succeed.  (This is weird, but it's efficient for the callers.)
  */
 static int
-XLogFileInitInternal(XLogSegNo logsegno, bool *added, char *path)
+XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
+					 bool *added, char *path)
 {
 	char		tmppath[MAXPGPATH];
 	PGAlignedXLogBlock zbuffer;
@@ -3305,7 +3307,9 @@ XLogFileInitInternal(XLogSegNo logsegno, bool *added, char *path)
 	int			fd;
 	int			save_errno;
 
-	XLogFilePath(path, ThisTimeLineID, logsegno, wal_segment_size);
+	Assert(logtli != 0);
+
+	XLogFilePath(path, logtli, logsegno, wal_segment_size);
 
 	/*
 	 * Try to use existent file (checkpoint maker may have created it already)
@@ -3449,7 +3453,8 @@ XLogFileInitInternal(XLogSegNo logsegno, bool *added, char *path)
 	 * CheckPointSegments.
 	 */
 	max_segno = logsegno + CheckPointSegments;
-	if (InstallXLogFileSegment(&installed_segno, tmppath, true, max_segno))
+	if (InstallXLogFileSegment(&installed_segno, tmppath, true, max_segno,
+							   logtli))
 	{
 		*added = true;
 		elog(DEBUG2, "done creating and filling new WAL file");
@@ -3481,13 +3486,15 @@ XLogFileInitInternal(XLogSegNo logsegno, bool *added, char *path)
  * in a critical section.
  */
 int
-XLogFileInit(XLogSegNo logsegno)
+XLogFileInit(XLogSegNo logsegno, TimeLineID logtli)
 {
 	bool		ignore_added;
 	char		path[MAXPGPATH];
 	int			fd;
 
-	fd = XLogFileInitInternal(logsegno, &ignore_added, path);
+	Assert(logtli != 0);
+
+	fd = XLogFileInitInternal(logsegno, logtli, &ignore_added, path);
 	if (fd >= 0)
 		return fd;
 
@@ -3629,7 +3636,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 	/*
 	 * Now move the segment into place with its final name.
 	 */
-	if (!InstallXLogFileSegment(&destsegno, tmppath, false, 0))
+	if (!InstallXLogFileSegment(&destsegno, tmppath, false, 0, ThisTimeLineID))
 		elog(ERROR, "InstallXLogFileSegment should not have failed");
 }
 
@@ -3653,18 +3660,22 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
  * free slot is found between *segno and max_segno. (Ignored when find_free
  * is false.)
  *
+ * tli: The timeline on which the new segment should be installed.
+ *
  * Returns true if the file was installed successfully.  false indicates that
  * max_segno limit was exceeded, the startup process has disabled this
  * function for now, or an error occurred while renaming the file into place.
  */
 static bool
 InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
-					   bool find_free, XLogSegNo max_segno)
+					   bool find_free, XLogSegNo max_segno, TimeLineID tli)
 {
 	char		path[MAXPGPATH];
 	struct stat stat_buf;
 
-	XLogFilePath(path, ThisTimeLineID, *segno, wal_segment_size);
+	Assert(tli != 0);
+
+	XLogFilePath(path, tli, *segno, wal_segment_size);
 
 	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
 	if (!XLogCtl->InstallXLogFileSegmentActive)
@@ -3690,7 +3701,7 @@ InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
 				return false;
 			}
 			(*segno)++;
-			XLogFilePath(path, ThisTimeLineID, *segno, wal_segment_size);
+			XLogFilePath(path, tli, *segno, wal_segment_size);
 		}
 	}
 
@@ -3987,7 +3998,7 @@ PreallocXlogFiles(XLogRecPtr endptr)
 	if (offset >= (uint32) (0.75 * wal_segment_size))
 	{
 		_logSegNo++;
-		lf = XLogFileInitInternal(_logSegNo, &added, path);
+		lf = XLogFileInitInternal(_logSegNo, ThisTimeLineID, &added, path);
 		if (lf >= 0)
 			close(lf);
 		if (added)
@@ -4266,7 +4277,7 @@ RemoveXlogFile(const char *segname, XLogSegNo recycleSegNo,
 		XLogCtl->InstallXLogFileSegmentActive &&	/* callee rechecks this */
 		lstat(path, &statbuf) == 0 && S_ISREG(statbuf.st_mode) &&
 		InstallXLogFileSegment(endlogSegNo, path,
-							   true, recycleSegNo))
+							   true, recycleSegNo, ThisTimeLineID))
 	{
 		ereport(DEBUG2,
 				(errmsg_internal("recycled write-ahead log file \"%s\"",
@@ -5401,7 +5412,7 @@ BootStrapXLOG(void)
 	record->xl_crc = crc;
 
 	/* Create first XLOG segment file */
-	openLogFile = XLogFileInit(1);
+	openLogFile = XLogFileInit(1, ThisTimeLineID);
 
 	/*
 	 * We needn't bother with Reserve/ReleaseExternalFD here, since we'll
@@ -5709,7 +5720,7 @@ exitArchiveRecovery(TimeLineID endTLI, XLogRecPtr endOfLog)
 		 */
 		int			fd;
 
-		fd = XLogFileInit(startLogSegNo);
+		fd = XLogFileInit(startLogSegNo, ThisTimeLineID);
 
 		if (close(fd) != 0)
 		{
@@ -8706,15 +8717,35 @@ GetInsertRecPtr(void)
  * position known to be fsync'd to disk.
  */
 XLogRecPtr
-GetFlushRecPtr(void)
+GetFlushRecPtr(TimeLineID *insertTLI)
 {
 	SpinLockAcquire(&XLogCtl->info_lck);
 	LogwrtResult = XLogCtl->LogwrtResult;
 	SpinLockRelease(&XLogCtl->info_lck);
 
+	/*
+	 * If we're writing and flushing WAL, the time line can't be changing,
+	 * so no lock is required.
+	 */
+	if (insertTLI)
+		*insertTLI = XLogCtl->ThisTimeLineID;
+
 	return LogwrtResult.Flush;
 }
 
+/*
+ * GetWALInsertionTimeLine -- Returns the current timeline of a system that
+ * is not in recovery.
+ */
+TimeLineID
+GetWALInsertionTimeLine(void)
+{
+	Assert(XLogCtl->SharedRecoveryState == RECOVERY_STATE_DONE);
+
+	/* Since the value can't be changing, no lock is required. */
+	return XLogCtl->ThisTimeLineID;
+}
+
 /*
  * GetLastImportantRecPtr -- Returns the LSN of the last important record
  * inserted. All records not explicitly marked as unimportant are considered
@@ -10849,11 +10880,13 @@ assign_xlog_sync_method(int new_sync_method, void *extra)
  * 'segno' is for error reporting purposes.
  */
 void
-issue_xlog_fsync(int fd, XLogSegNo segno)
+issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 {
 	char	   *msg = NULL;
 	instr_time	start;
 
+	Assert(tli != 0);
+
 	/*
 	 * Quick exit if fsync is disabled or write() has already synced the WAL
 	 * file.
@@ -10902,8 +10935,7 @@ issue_xlog_fsync(int fd, XLogSegNo segno)
 		char		xlogfname[MAXFNAMELEN];
 		int			save_errno = errno;
 
-		XLogFileName(xlogfname, ThisTimeLineID, segno,
-					 wal_segment_size);
+		XLogFileName(xlogfname, tli, segno, wal_segment_size);
 		errno = save_errno;
 		ereport(PANIC,
 				(errcode_for_file_access(),

src/backend/access/transam/xlogarchive.c

@@ -498,11 +498,13 @@ XLogArchiveNotify(const char *xlog)
  * Convenience routine to notify using segment number representation of filename
  */
 void
-XLogArchiveNotifySeg(XLogSegNo segno)
+XLogArchiveNotifySeg(XLogSegNo segno, TimeLineID tli)
 {
 	char		xlog[MAXFNAMELEN];
 
-	XLogFileName(xlog, ThisTimeLineID, segno, wal_segment_size);
+	Assert(tli != 0);
+
+	XLogFileName(xlog, tli, segno, wal_segment_size);
 	XLogArchiveNotify(xlog);
 }
 

src/backend/access/transam/xlogfuncs.c

@@ -382,7 +382,7 @@ pg_current_wal_flush_lsn(PG_FUNCTION_ARGS)
 				 errmsg("recovery is in progress"),
 				 errhint("WAL control functions cannot be executed during recovery.")));
 
-	current_recptr = GetFlushRecPtr();
+	current_recptr = GetFlushRecPtr(NULL);
 
 	PG_RETURN_LSN(current_recptr);
 }
@@ -469,7 +469,8 @@ pg_walfile_name_offset(PG_FUNCTION_ARGS)
 	 * xlogfilename
 	 */
 	XLByteToPrevSeg(locationpoint, xlogsegno, wal_segment_size);
-	XLogFileName(xlogfilename, ThisTimeLineID, xlogsegno, wal_segment_size);
+	XLogFileName(xlogfilename, GetWALInsertionTimeLine(), xlogsegno,
+				 wal_segment_size);
 
 	values[0] = CStringGetTextDatum(xlogfilename);
 	isnull[0] = false;
@@ -511,7 +512,8 @@ pg_walfile_name(PG_FUNCTION_ARGS)
 						 "pg_walfile_name()")));
 
 	XLByteToPrevSeg(locationpoint, xlogsegno, wal_segment_size);
-	XLogFileName(xlogfilename, ThisTimeLineID, xlogsegno, wal_segment_size);
+	XLogFileName(xlogfilename, GetWALInsertionTimeLine(), xlogsegno,
+				 wal_segment_size);
 
 	PG_RETURN_TEXT_P(cstring_to_text(xlogfilename));
 }