From b71a67d21df2028396a533097d74a828ed421f3f Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Mon, 1 Nov 2021 14:39:36 -0400
Subject: [PATCH] Demote ThisTimeLineID to a local variable.

Instead of a file-level global variable, it can now be made local
to StartupXLOG. The only other code that still accesses it is in
BootstrapXLOG, where we now just use a constant instead.
---
 src/backend/access/transam/xlog.c | 35 ++++++++++---------------------
 1 file changed, 11 insertions(+), 24 deletions(-)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8a650b875e..dcc215dcc2 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -88,6 +88,9 @@ extern uint32 bootstrap_data_checksum_version;
 #define RECOVERY_COMMAND_FILE	"recovery.conf"
 #define RECOVERY_COMMAND_DONE	"recovery.done"
 
+/* timeline ID to be used when bootstrapping */
+#define BootstrapTimeLineID		1
+
 /* User-settable parameters */
 int			max_wal_size_mb = 1024; /* 1 GB */
 int			min_wal_size_mb = 80;	/* 80 MB */
@@ -188,12 +191,6 @@ const struct config_enum_entry recovery_target_action_options[] = {
  */
 CheckpointStatsData CheckpointStats;
 
-/*
- * ThisTimeLineID will be same in all backends --- it identifies current
- * WAL timeline for the database system.
- */
-static TimeLineID	ThisTimeLineID = 0;
-
 static XLogRecPtr LastRec;
 
 /* Local copy of WalRcv->flushedUpto */
@@ -5368,9 +5365,6 @@ BootStrapXLOG(void)
 	sysidentifier |= ((uint64) tv.tv_usec) << 12;
 	sysidentifier |= getpid() & 0xFFF;
 
-	/* First timeline ID is always 1 */
-	ThisTimeLineID = 1;
-
 	/* page buffer must be aligned suitably for O_DIRECT */
 	buffer = (char *) palloc(XLOG_BLCKSZ + XLOG_BLCKSZ);
 	page = (XLogPageHeader) TYPEALIGN(XLOG_BLCKSZ, buffer);
@@ -5384,8 +5378,8 @@ BootStrapXLOG(void)
 	 * used, so that we can use 0/0 to mean "before any valid WAL segment".
 	 */
 	checkPoint.redo = wal_segment_size + SizeOfXLogLongPHD;
-	checkPoint.ThisTimeLineID = ThisTimeLineID;
-	checkPoint.PrevTimeLineID = ThisTimeLineID;
+	checkPoint.ThisTimeLineID = BootstrapTimeLineID;
+	checkPoint.PrevTimeLineID = BootstrapTimeLineID;
 	checkPoint.fullPageWrites = fullPageWrites;
 	checkPoint.nextXid =
 		FullTransactionIdFromEpochAndXid(0, FirstNormalTransactionId);
@@ -5413,7 +5407,7 @@ BootStrapXLOG(void)
 	/* Set up the XLOG page header */
 	page->xlp_magic = XLOG_PAGE_MAGIC;
 	page->xlp_info = XLP_LONG_HEADER;
-	page->xlp_tli = ThisTimeLineID;
+	page->xlp_tli = BootstrapTimeLineID;
 	page->xlp_pageaddr = wal_segment_size;
 	longpage = (XLogLongPageHeader) page;
 	longpage->xlp_sysid = sysidentifier;
@@ -5443,8 +5437,8 @@ BootStrapXLOG(void)
 	record->xl_crc = crc;
 
 	/* Create first XLOG segment file */
-	openLogTLI = ThisTimeLineID;
-	openLogFile = XLogFileInit(1, ThisTimeLineID);
+	openLogTLI = BootstrapTimeLineID;
+	openLogFile = XLogFileInit(1, BootstrapTimeLineID);
 
 	/*
 	 * We needn't bother with Reserve/ReleaseExternalFD here, since we'll
@@ -6681,7 +6675,8 @@ StartupXLOG(void)
 				checkPointLoc,
 				EndOfLog;
 	TimeLineID	EndOfLogTLI;
-	TimeLineID	PrevTimeLineID;
+	TimeLineID	ThisTimeLineID,
+				PrevTimeLineID;
 	XLogRecord *record;
 	TransactionId oldestActiveXID;
 	bool		backupEndRequired = false;
@@ -8661,21 +8656,13 @@ ReadCheckpointRecord(XLogReaderState *xlogreader, XLogRecPtr RecPtr,
 /*
  * This must be called in a backend process before creating WAL records
  * (except in a standalone backend, which does StartupXLOG instead).  We need
- * to initialize the local copies of ThisTimeLineID and RedoRecPtr.
- *
- * Note: before Postgres 8.0, we went to some effort to keep the postmaster
- * process's copies of ThisTimeLineID and RedoRecPtr valid too.  This was
- * unnecessary however, since the postmaster itself never touches XLOG anyway.
+ * to initialize the local copy of RedoRecPtr.
  */
 void
 InitXLOGAccess(void)
 {
 	XLogCtlInsert *Insert = &XLogCtl->Insert;
 
-	/* ThisTimeLineID doesn't change so we need no lock to copy it */
-	ThisTimeLineID = XLogCtl->ThisTimeLineID;
-	Assert(ThisTimeLineID != 0 || IsBootstrapProcessingMode());
-
 	/* set wal_segment_size */
 	wal_segment_size = ControlFile->xlog_seg_size;
 
-- 
2.39.5