From a39ffddc1c525fa4e39fd08657c6dae95a20043f Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Tue, 18 Jun 2024 11:00:36 +0900
Subject: [PATCH 1/4] Add redo LSN to pgstats file

This is used in the startup process to check that the file we are
loading is the one referring to the latest checkpoint.

Bump PGSTAT_FILE_FORMAT_ID.
---
 src/include/pgstat.h                |  5 +++--
 src/backend/access/transam/xlog.c   |  2 +-
 src/backend/utils/activity/pgstat.c | 26 +++++++++++++++++++-------
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 2136239710..dbc3430b18 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -11,6 +11,7 @@
 #ifndef PGSTAT_H
 #define PGSTAT_H
 
+#include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "portability/instr_time.h"
 #include "postmaster/pgarch.h"	/* for MAX_XFN_CHARS */
@@ -235,7 +236,7 @@ typedef struct PgStat_TableXactStatus
  * ------------------------------------------------------------
  */
 
-#define PGSTAT_FILE_FORMAT_ID	0x01A5BCAC
+#define PGSTAT_FILE_FORMAT_ID	0x01A5BCAD
 
 typedef struct PgStat_ArchiverStats
 {
@@ -466,7 +467,7 @@ extern Size StatsShmemSize(void);
 extern void StatsShmemInit(void);
 
 /* Functions called during server startup / shutdown */
-extern void pgstat_restore_stats(void);
+extern void pgstat_restore_stats(XLogRecPtr redo);
 extern void pgstat_discard_stats(void);
 extern void pgstat_before_server_shutdown(int code, Datum arg);
 
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 330e058c5f..96b458da42 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5641,7 +5641,7 @@ StartupXLOG(void)
 	if (didCrash)
 		pgstat_discard_stats();
 	else
-		pgstat_restore_stats();
+		pgstat_restore_stats(checkPoint.redo);
 
 	lastFullPageWrites = checkPoint.fullPageWrites;
 
diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c
index dcc2ad8d95..824f742bde 100644
--- a/src/backend/utils/activity/pgstat.c
+++ b/src/backend/utils/activity/pgstat.c
@@ -94,6 +94,7 @@
 #include <unistd.h>
 
 #include "access/xact.h"
+#include "access/xlog.h"
 #include "lib/dshash.h"
 #include "pgstat.h"
 #include "port/atomics.h"
@@ -162,8 +163,8 @@ typedef struct PgStat_SnapshotEntry
  * ----------
  */
 
-static void pgstat_write_statsfile(void);
-static void pgstat_read_statsfile(void);
+static void pgstat_write_statsfile(XLogRecPtr redo);
+static void pgstat_read_statsfile(XLogRecPtr redo);
 
 static void pgstat_reset_after_failure(void);
 
@@ -404,9 +405,9 @@ static const PgStat_KindInfo pgstat_kind_infos[PGSTAT_NUM_KINDS] = {
  * Should only be called by the startup process or in single user mode.
  */
 void
-pgstat_restore_stats(void)
+pgstat_restore_stats(XLogRecPtr redo)
 {
-	pgstat_read_statsfile();
+	pgstat_read_statsfile(redo);
 }
 
 /*
@@ -482,7 +483,7 @@ pgstat_before_server_shutdown(int code, Datum arg)
 	if (code == 0)
 	{
 		pgStatLocal.shmem->is_shutdown = true;
-		pgstat_write_statsfile();
+		pgstat_write_statsfile(GetRedoRecPtr());
 	}
 }
 
@@ -1305,7 +1306,7 @@ write_chunk(FILE *fpout, void *ptr, size_t len)
  * stats so locking is not required.
  */
 static void
-pgstat_write_statsfile(void)
+pgstat_write_statsfile(XLogRecPtr redo)
 {
 	FILE	   *fpout;
 	int32		format_id;
@@ -1340,6 +1341,9 @@ pgstat_write_statsfile(void)
 	format_id = PGSTAT_FILE_FORMAT_ID;
 	write_chunk_s(fpout, &format_id);
 
+	/* Write the redo LSN, used to cross check the file loaded */
+	write_chunk_s(fpout, &redo);
+
 	/*
 	 * XXX: The following could now be generalized to just iterate over
 	 * pgstat_kind_infos instead of knowing about the different kinds of
@@ -1480,13 +1484,14 @@ read_chunk(FILE *fpin, void *ptr, size_t len)
  * stats so locking is not required.
  */
 static void
-pgstat_read_statsfile(void)
+pgstat_read_statsfile(XLogRecPtr redo)
 {
 	FILE	   *fpin;
 	int32		format_id;
 	bool		found;
 	const char *statfile = PGSTAT_STAT_PERMANENT_FILENAME;
 	PgStat_ShmemControl *shmem = pgStatLocal.shmem;
+	XLogRecPtr	file_redo;
 
 	/* shouldn't be called from postmaster */
 	Assert(IsUnderPostmaster || !IsPostmasterEnvironment);
@@ -1520,6 +1525,13 @@ pgstat_read_statsfile(void)
 		format_id != PGSTAT_FILE_FORMAT_ID)
 		goto error;
 
+	/*
+	 * Read the redo LSN stored in the file.
+	 */
+	if (!read_chunk_s(fpin, &file_redo) ||
+		file_redo != redo)
+		goto error;
+
 	/*
 	 * XXX: The following could now be generalized to just iterate over
 	 * pgstat_kind_infos instead of knowing about the different kinds of
-- 
2.45.1