Revert "Add redo LSN to pgstats files"

michaelpq · michaelpq · commit 5721e5453ebc · 2025-03-17T08:35:12.000+09:00
This reverts commit b860848, that was added as a prerequisite for the support of pgstats data flush across checkpoints, linking a pgstats file to a specific checkpoint redo LSN. As reported, this is proving to be currently problematic when going through a pg_upgrade, that does direct manipulations of the control file in the new cluster. The LSN stored in the pgstats file is not able to cope with any changes done in the control file by pg_upgrade yet, causing the pgstats file to be discarded when starting the new cluster after overriding its redo LSN (one is a `pg_resetwal -l` where the new cluster's start LSN is bumped by a hardcoded value of 8 segments, see copy_xact_xlog_xid). The least painful path going forward is likely going to be a refactor of the pgstats code so as it is possible to read and write some of its data with some routines in src/common/, so as pg_upgrade or pg_resetwal are able to update its data. The main point is that we are going to need a LSN in the stats file should we make it written at checkpoint time and not only as part of a shutdown sequence. It is too late to dive into these details for v18, so let's revert the change, and let's try to figure out all the details in the next release cycle. The pgstats file is currently only written as part of a shutdown sequence, and its contents are still lost on crash, same as older releases. Bump PGSTAT_FILE_FORMAT_ID. Reported-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/2563883.1741826489@sss.pgh.pa.us
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
@@ -5728,7 +5728,7 @@ StartupXLOG(void)
 	if (didCrash)
 		pgstat_discard_stats();
 	else
-		pgstat_restore_stats(checkPoint.redo);
+		pgstat_restore_stats();
 
 	lastFullPageWrites = checkPoint.fullPageWrites;
 
diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c
@@ -104,7 +104,6 @@
 #include <unistd.h>
 
 #include "access/xact.h"
-#include "access/xlog.h"
 #include "lib/dshash.h"
 #include "pgstat.h"
 #include "storage/fd.h"
@@ -181,8 +180,8 @@ typedef struct PgStat_SnapshotEntry
  * ----------
  */
 
-static void pgstat_write_statsfile(XLogRecPtr redo);
-static void pgstat_read_statsfile(XLogRecPtr redo);
+static void pgstat_write_statsfile(void);
+static void pgstat_read_statsfile(void);
 
 static void pgstat_init_snapshot_fixed(void);
 
@@ -503,9 +502,9 @@ static const PgStat_KindInfo **pgstat_kind_custom_infos = NULL;
  * Should only be called by the startup process or in single user mode.
  */
 void
-pgstat_restore_stats(XLogRecPtr redo)
+pgstat_restore_stats(void)
 {
-	pgstat_read_statsfile(redo);
+	pgstat_read_statsfile();
 }
 
 /*
@@ -581,7 +580,7 @@ pgstat_before_server_shutdown(int code, Datum arg)
 	if (code == 0)
 	{
 		pgStatLocal.shmem->is_shutdown = true;
-		pgstat_write_statsfile(GetRedoRecPtr());
+		pgstat_write_statsfile();
 	}
 }
 
@@ -1585,7 +1584,7 @@ write_chunk(FILE *fpout, void *ptr, size_t len)
  * stats so locking is not required.
  */
 static void
-pgstat_write_statsfile(XLogRecPtr redo)
+pgstat_write_statsfile(void)
 {
 	FILE	   *fpout;
 	int32		format_id;
@@ -1602,8 +1601,7 @@ pgstat_write_statsfile(XLogRecPtr redo)
 	/* we're shutting down, so it's ok to just override this */
 	pgstat_fetch_consistency = PGSTAT_FETCH_CONSISTENCY_NONE;
 
-	elog(DEBUG2, "writing stats file \"%s\" with redo %X/%X", statfile,
-		 LSN_FORMAT_ARGS(redo));
+	elog(DEBUG2, "writing stats file \"%s\"", statfile);
 
 	/*
 	 * Open the statistics temp file to write out the current values.
@@ -1624,9 +1622,6 @@ pgstat_write_statsfile(XLogRecPtr redo)
 	format_id = PGSTAT_FILE_FORMAT_ID;
 	write_chunk_s(fpout, &format_id);
 
-	/* Write the redo LSN, used to cross check the file read */
-	write_chunk_s(fpout, &redo);
-
 	/* Write various stats structs for fixed number of objects */
 	for (PgStat_Kind kind = PGSTAT_KIND_MIN; kind <= PGSTAT_KIND_MAX; kind++)
 	{
@@ -1773,20 +1768,18 @@ read_chunk(FILE *fpin, void *ptr, size_t len)
  * stats so locking is not required.
  */
 static void
-pgstat_read_statsfile(XLogRecPtr redo)
+pgstat_read_statsfile(void)
 {
 	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);
 
-	elog(DEBUG2, "reading stats file \"%s\" with redo %X/%X", statfile,
-		 LSN_FORMAT_ARGS(redo));
+	elog(DEBUG2, "reading stats file \"%s\"", statfile);
 
 	/*
 	 * Try to open the stats file. If it doesn't exist, the backends simply
@@ -1824,22 +1817,6 @@ pgstat_read_statsfile(XLogRecPtr redo)
 		goto error;
 	}
 
-	/*
-	 * Read the redo LSN stored in the file.
-	 */
-	if (!read_chunk_s(fpin, &file_redo))
-	{
-		elog(WARNING, "could not read redo LSN");
-		goto error;
-	}
-
-	if (file_redo != redo)
-	{
-		elog(WARNING, "found incorrect redo LSN %X/%X (expected %X/%X)",
-			 LSN_FORMAT_ARGS(file_redo), LSN_FORMAT_ARGS(redo));
-		goto error;
-	}
-
 	/*
 	 * We found an existing statistics file. Read it and put all the stats
 	 * data into place.
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
@@ -11,7 +11,6 @@
 #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 */
@@ -212,7 +211,7 @@ typedef struct PgStat_TableXactStatus
  * ------------------------------------------------------------
  */
 
-#define PGSTAT_FILE_FORMAT_ID	0x01A5BCB5
+#define PGSTAT_FILE_FORMAT_ID	0x01A5BCB6
 
 typedef struct PgStat_ArchiverStats
 {
@@ -514,7 +513,7 @@ extern Size StatsShmemSize(void);
 extern void StatsShmemInit(void);
 
 /* Functions called during server startup / shutdown */
-extern void pgstat_restore_stats(XLogRecPtr redo);
+extern void pgstat_restore_stats(void);
 extern void pgstat_discard_stats(void);
 extern void pgstat_before_server_shutdown(int code, Datum arg);
 
