WAL-logging facility for pgstats kinds

From 55a3c446c44f32204a070ca33c6ac01a16a2da3d Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 27 Dec 2024 11:54:45 +0900
Subject: [PATCH v2 2/4] Move information about pgstats kinds into its own
 header

This information is split into its own header as it will be used by a
follow-up patch, to be used in some frontend and backend code.
---
 src/include/pgstat.h            | 57 +-------------------------
 src/include/utils/pgstat_kind.h | 72 +++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+), 56 deletions(-)
 create mode 100644 src/include/utils/pgstat_kind.h

diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 75a41e8ff3..601b8075d5 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -18,6 +18,7 @@
 #include "replication/conflict.h"
 #include "utils/backend_progress.h" /* for backward compatibility */
 #include "utils/backend_status.h"	/* for backward compatibility */
+#include "utils/pgstat_kind.h"
 #include "utils/relcache.h"
 #include "utils/wait_event.h"	/* for backward compatibility */
 
@@ -33,62 +34,6 @@
 /* Default directory to store temporary statistics data in */
 #define PG_STAT_TMP_DIR		"pg_stat_tmp"
 
-/* The types of statistics entries */
-#define PgStat_Kind uint32
-
-/* Range of IDs allowed, for built-in and custom kinds */
-#define PGSTAT_KIND_MIN	1		/* Minimum ID allowed */
-#define PGSTAT_KIND_MAX	256		/* Maximum ID allowed */
-
-/* use 0 for INVALID, to catch zero-initialized data */
-#define PGSTAT_KIND_INVALID 0
-
-/* stats for variable-numbered objects */
-#define PGSTAT_KIND_DATABASE	1	/* database-wide statistics */
-#define PGSTAT_KIND_RELATION	2	/* per-table statistics */
-#define PGSTAT_KIND_FUNCTION	3	/* per-function statistics */
-#define PGSTAT_KIND_REPLSLOT	4	/* per-slot statistics */
-#define PGSTAT_KIND_SUBSCRIPTION	5	/* per-subscription statistics */
-#define PGSTAT_KIND_BACKEND	6	/* per-backend statistics */
-
-/* stats for fixed-numbered objects */
-#define PGSTAT_KIND_ARCHIVER	7
-#define PGSTAT_KIND_BGWRITER	8
-#define PGSTAT_KIND_CHECKPOINTER	9
-#define PGSTAT_KIND_IO	10
-#define PGSTAT_KIND_SLRU	11
-#define PGSTAT_KIND_WAL	12
-
-#define PGSTAT_KIND_BUILTIN_MIN PGSTAT_KIND_DATABASE
-#define PGSTAT_KIND_BUILTIN_MAX PGSTAT_KIND_WAL
-#define PGSTAT_KIND_BUILTIN_SIZE (PGSTAT_KIND_BUILTIN_MAX + 1)
-
-/* Custom stats kinds */
-
-/* Range of IDs allowed for custom stats kinds */
-#define PGSTAT_KIND_CUSTOM_MIN	128
-#define PGSTAT_KIND_CUSTOM_MAX	PGSTAT_KIND_MAX
-#define PGSTAT_KIND_CUSTOM_SIZE	(PGSTAT_KIND_CUSTOM_MAX - PGSTAT_KIND_CUSTOM_MIN + 1)
-
-/*
- * PgStat_Kind to use for extensions that require an ID, but are still in
- * development and have not reserved their own unique kind ID yet. See:
- * https://wiki.postgresql.org/wiki/CustomCumulativeStats
- */
-#define PGSTAT_KIND_EXPERIMENTAL	128
-
-static inline bool
-pgstat_is_kind_builtin(PgStat_Kind kind)
-{
-	return kind >= PGSTAT_KIND_BUILTIN_MIN && kind <= PGSTAT_KIND_BUILTIN_MAX;
-}
-
-static inline bool
-pgstat_is_kind_custom(PgStat_Kind kind)
-{
-	return kind >= PGSTAT_KIND_CUSTOM_MIN && kind <= PGSTAT_KIND_CUSTOM_MAX;
-}
-
 /* Values for track_functions GUC variable --- order is significant! */
 typedef enum TrackFunctionsLevel
 {
diff --git a/src/include/utils/pgstat_kind.h b/src/include/utils/pgstat_kind.h
new file mode 100644
index 0000000000..526fa04e8f
--- /dev/null
+++ b/src/include/utils/pgstat_kind.h
@@ -0,0 +1,72 @@
+/* ----------
+ *	pgstat_kind.h
+ *
+ *	Definitions related to the statistics kinds for the PostgreSQL
+ *	cumulative statistics system.  Can be included in backend or
+ *	frontend code.
+ *
+ *	Copyright (c) 2001-2024, PostgreSQL Global Development Group
+ *
+ *	src/include/utils/pgstat_kind.h
+ * ----------
+ */
+#ifndef PGSTAT_KIND_H
+#define PGSTAT_KIND_H
+
+/* The types of statistics entries */
+#define PgStat_Kind uint32
+
+/* Range of IDs allowed, for built-in and custom kinds */
+#define PGSTAT_KIND_MIN	1		/* Minimum ID allowed */
+#define PGSTAT_KIND_MAX	256		/* Maximum ID allowed */
+
+/* use 0 for INVALID, to catch zero-initialized data */
+#define PGSTAT_KIND_INVALID 0
+
+/* stats for variable-numbered objects */
+#define PGSTAT_KIND_DATABASE	1	/* database-wide statistics */
+#define PGSTAT_KIND_RELATION	2	/* per-table statistics */
+#define PGSTAT_KIND_FUNCTION	3	/* per-function statistics */
+#define PGSTAT_KIND_REPLSLOT	4	/* per-slot statistics */
+#define PGSTAT_KIND_SUBSCRIPTION	5	/* per-subscription statistics */
+#define PGSTAT_KIND_BACKEND	6	/* per-backend statistics */
+
+/* stats for fixed-numbered objects */
+#define PGSTAT_KIND_ARCHIVER	7
+#define PGSTAT_KIND_BGWRITER	8
+#define PGSTAT_KIND_CHECKPOINTER	9
+#define PGSTAT_KIND_IO	10
+#define PGSTAT_KIND_SLRU	11
+#define PGSTAT_KIND_WAL	12
+
+#define PGSTAT_KIND_BUILTIN_MIN PGSTAT_KIND_DATABASE
+#define PGSTAT_KIND_BUILTIN_MAX PGSTAT_KIND_WAL
+#define PGSTAT_KIND_BUILTIN_SIZE (PGSTAT_KIND_BUILTIN_MAX + 1)
+
+/* Custom stats kinds */
+
+/* Range of IDs allowed for custom stats kinds */
+#define PGSTAT_KIND_CUSTOM_MIN	128
+#define PGSTAT_KIND_CUSTOM_MAX	PGSTAT_KIND_MAX
+#define PGSTAT_KIND_CUSTOM_SIZE	(PGSTAT_KIND_CUSTOM_MAX - PGSTAT_KIND_CUSTOM_MIN + 1)
+
+/*
+ * PgStat_Kind to use for extensions that require an ID, but are still in
+ * development and have not reserved their own unique kind ID yet. See:
+ * https://wiki.postgresql.org/wiki/CustomCumulativeStats
+ */
+#define PGSTAT_KIND_EXPERIMENTAL	128
+
+static inline bool
+pgstat_is_kind_builtin(PgStat_Kind kind)
+{
+	return kind >= PGSTAT_KIND_BUILTIN_MIN && kind <= PGSTAT_KIND_BUILTIN_MAX;
+}
+
+static inline bool
+pgstat_is_kind_custom(PgStat_Kind kind)
+{
+	return kind >= PGSTAT_KIND_CUSTOM_MIN && kind <= PGSTAT_KIND_CUSTOM_MAX;
+}
+
+#endif							/* PGSTAT_KIND_H */
-- 
2.45.2

From 2fd2b76238618e62e37eb011c0fe145162602a9d Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 27 Dec 2024 12:03:34 +0900
Subject: [PATCH v2 3/4] Add RMGR and WAL-logging API for pgstats

This commit adds a new facility in the backend that offers to pgstats
kinds the possibility to WAL-log data that need to be persisted across
restarts:
- A new callback called redo_cb can be defined by a pgstats_kind.
- pgstat_xlog.c includes one API able to register some payload data and
its size.  Stats kinds doing WAL-logging require a definition of
redo_cb.
- pg_waldump is able to show the data logged, as hexadedimal data.

This facility has applications for in-core and custom stats kinds, with
one primary case being the possibility to WAL-log some statistics
related to relations so as these are not lost post-crash.  This is left
as future work.
---
 src/include/access/rmgrlist.h            |  1 +
 src/include/utils/pgstat_internal.h      |  8 +++
 src/include/utils/pgstat_xlog.h          | 41 +++++++++++++
 src/backend/access/rmgrdesc/Makefile     |  1 +
 src/backend/access/rmgrdesc/meson.build  |  1 +
 src/backend/access/rmgrdesc/pgstatdesc.c | 48 +++++++++++++++
 src/backend/access/transam/rmgr.c        |  1 +
 src/backend/utils/activity/Makefile      |  1 +
 src/backend/utils/activity/meson.build   |  1 +
 src/backend/utils/activity/pgstat_xlog.c | 77 ++++++++++++++++++++++++
 src/bin/pg_waldump/.gitignore            |  1 +
 src/bin/pg_waldump/rmgrdesc.c            |  1 +
 src/bin/pg_waldump/t/001_basic.pl        |  3 +-
 src/tools/pgindent/typedefs.list         |  1 +
 14 files changed, 185 insertions(+), 1 deletion(-)
 create mode 100644 src/include/utils/pgstat_xlog.h
 create mode 100644 src/backend/access/rmgrdesc/pgstatdesc.c
 create mode 100644 src/backend/utils/activity/pgstat_xlog.c

diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index 78e6b908c6..abf9393bbe 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -47,3 +47,4 @@ PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_i
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL, NULL, NULL)
 PG_RMGR(RM_GENERIC_ID, "Generic", generic_redo, generic_desc, generic_identify, NULL, NULL, generic_mask, NULL)
 PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL, NULL, logicalmsg_decode)
+PG_RMGR(RM_PGSTAT_ID, "PgStat", pgstat_redo, pgstat_desc, pgstat_identify, NULL, NULL, NULL, NULL)
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 811ed9b005..47d7f8988e 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -258,6 +258,14 @@ typedef struct PgStat_KindInfo
 	 */
 	void		(*init_backend_cb) (void);
 
+	/*
+	 * Perform custom actions when replaying WAL related to a statistics kind.
+	 *
+	 * "data" is a pointer to the stats information that can be used by the
+	 * stats kind at redo.
+	 */
+	void		(*redo_cb) (void *data, size_t data_size);
+
 	/*
 	 * For variable-numbered stats: flush pending stats. Required if pending
 	 * data is used.  See flush_fixed_cb for fixed-numbered stats.
diff --git a/src/include/utils/pgstat_xlog.h b/src/include/utils/pgstat_xlog.h
new file mode 100644
index 0000000000..25b7a78dd5
--- /dev/null
+++ b/src/include/utils/pgstat_xlog.h
@@ -0,0 +1,41 @@
+/* ----------
+ * pgstat_xlog.h
+ *	  Exports from utils/activity/pgstat_xlog.c
+ *
+ * Copyright (c) 2001-2024, PostgreSQL Global Development Group
+ *
+ * src/include/utils/pgstat_xlog.h
+ * ----------
+ */
+#ifndef PGSTAT_XLOG_H
+#define PGSTAT_XLOG_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+#include "utils/pgstat_kind.h"
+
+/*
+ * Generic WAL record for pgstat data.
+ */
+typedef struct xl_pgstat_data
+{
+	PgStat_Kind stats_kind;
+	size_t		data_size;		/* size of the data */
+	/* data payload, worth data_size */
+	char		data[FLEXIBLE_ARRAY_MEMBER];
+} xl_pgstat_data;
+
+#define SizeOfPgStatData    (offsetof(xl_pgstat_data, data))
+
+extern XLogRecPtr pgstat_xlog_data(PgStat_Kind stats_kind,
+								   const void *data,
+								   size_t data_size);
+
+/* RMGR API */
+#define XLOG_PGSTAT_DATA	0x00
+extern void pgstat_redo(XLogReaderState *record);
+extern void pgstat_desc(StringInfo buf, XLogReaderState *record);
+extern const char *pgstat_identify(uint8 info);
+
+#endif							/* PGSTAT_XLOG_H */
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index cd95eec37f..3979d22946 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -21,6 +21,7 @@ OBJS = \
 	logicalmsgdesc.o \
 	mxactdesc.o \
 	nbtdesc.o \
+	pgstatdesc.o \
 	relmapdesc.o \
 	replorigindesc.o \
 	rmgrdesc_utils.o \
diff --git a/src/backend/access/rmgrdesc/meson.build b/src/backend/access/rmgrdesc/meson.build
index e8b7a65fc7..951dacbd72 100644
--- a/src/backend/access/rmgrdesc/meson.build
+++ b/src/backend/access/rmgrdesc/meson.build
@@ -14,6 +14,7 @@ rmgr_desc_sources = files(
   'logicalmsgdesc.c',
   'mxactdesc.c',
   'nbtdesc.c',
+  'pgstatdesc.c',
   'relmapdesc.c',
   'replorigindesc.c',
   'rmgrdesc_utils.c',
diff --git a/src/backend/access/rmgrdesc/pgstatdesc.c b/src/backend/access/rmgrdesc/pgstatdesc.c
new file mode 100644
index 0000000000..0fc19d1e56
--- /dev/null
+++ b/src/backend/access/rmgrdesc/pgstatdesc.c
@@ -0,0 +1,48 @@
+/*-------------------------------------------------------------------------
+ *
+ * pgstatdesc.c
+ *	  rmgr descriptor routines for utils/activity/pgstat_xlog.c
+ *
+ * Portions Copyright (c) 2001-2024, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/pgstatdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "utils/pgstat_xlog.h"
+
+void
+pgstat_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_PGSTAT_DATA)
+	{
+		xl_pgstat_data *xlrec = (xl_pgstat_data *) rec;
+		char	   *sep = "";
+
+		appendStringInfo(buf, "stats kind \"%u\"; with data (%zu bytes): ",
+						 xlrec->stats_kind, xlrec->data_size);
+		/* Write data payload as a series of hex bytes */
+		for (int cnt = 0; cnt < xlrec->data_size; cnt++)
+		{
+			appendStringInfo(buf, "%s%02X", sep, (unsigned char) xlrec->data[cnt]);
+			sep = " ";
+		}
+	}
+}
+
+const char *
+pgstat_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_PGSTAT_DATA)
+		return "PGSTAT_DATA";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 1b7499726e..945843a78e 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -39,6 +39,7 @@
 #include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
+#include "utils/pgstat_xlog.h"
 #include "utils/relmapper.h"
 /* IWYU pragma: end_keep */
 
diff --git a/src/backend/utils/activity/Makefile b/src/backend/utils/activity/Makefile
index 24b64a2742..186108c60a 100644
--- a/src/backend/utils/activity/Makefile
+++ b/src/backend/utils/activity/Makefile
@@ -33,6 +33,7 @@ OBJS = \
 	pgstat_subscription.o \
 	pgstat_wal.o \
 	pgstat_xact.o \
+	pgstat_xlog.o \
 	wait_event.o \
 	wait_event_funcs.o
 
diff --git a/src/backend/utils/activity/meson.build b/src/backend/utils/activity/meson.build
index 380d3dd70c..a79e2d3731 100644
--- a/src/backend/utils/activity/meson.build
+++ b/src/backend/utils/activity/meson.build
@@ -18,6 +18,7 @@ backend_sources += files(
   'pgstat_subscription.c',
   'pgstat_wal.c',
   'pgstat_xact.c',
+  'pgstat_xlog.c',
 )
 
 # this includes a .c file with contents generated in ../../../include/activity,
diff --git a/src/backend/utils/activity/pgstat_xlog.c b/src/backend/utils/activity/pgstat_xlog.c
new file mode 100644
index 0000000000..397a49a33a
--- /dev/null
+++ b/src/backend/utils/activity/pgstat_xlog.c
@@ -0,0 +1,77 @@
+/* ----------
+ * pgstat_xlog.c
+ *	   WAL replay logic for cumulative statistics.
+ *
+ *
+ * Copyright (c) 2001-2024, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/activity/pgstat_xlog.c
+ * ----------
+ */
+
+#include "postgres.h"
+
+#include <unistd.h>
+
+#include "access/xlog.h"
+#include "access/xloginsert.h"
+#include "utils/pgstat_internal.h"
+#include "utils/pgstat_xlog.h"
+
+/*
+ * Write pgstats record data into WAL.
+ */
+XLogRecPtr
+pgstat_xlog_data(PgStat_Kind stats_kind, const void *data,
+				 size_t data_size)
+{
+	xl_pgstat_data xlrec;
+	XLogRecPtr	lsn;
+
+	xlrec.stats_kind = stats_kind;
+	xlrec.data_size = data_size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfPgStatData);
+	XLogRegisterData(data, data_size);
+
+	lsn = XLogInsert(RM_PGSTAT_ID, XLOG_PGSTAT_DATA);
+	return lsn;
+}
+
+/*
+ * Redo just passes down to the stats kind expected by this record
+ * data included in it.
+ */
+void
+pgstat_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+	xl_pgstat_data *xlrec;
+	PgStat_Kind stats_kind;
+	size_t		data_size;
+	void	   *data;
+	const PgStat_KindInfo *kind_info;
+
+	if (info != XLOG_PGSTAT_DATA)
+		elog(PANIC, "pgstat_redo: unknown op code %u", info);
+
+	xlrec = (xl_pgstat_data *) XLogRecGetData(record);
+
+	stats_kind = xlrec->stats_kind;
+	data_size = xlrec->data_size;
+	data = xlrec->data;
+
+	kind_info = pgstat_get_kind_info(stats_kind);
+
+	if (kind_info == NULL)
+		elog(FATAL, "pgstat_redo: invalid stats data found: kind=%u",
+			 stats_kind);
+
+	if (kind_info->redo_cb == NULL)
+		elog(FATAL, "pgstat_redo: no redo callback found: kind=%s",
+			 kind_info->name);
+
+	kind_info->redo_cb(data, data_size);
+}
diff --git a/src/bin/pg_waldump/.gitignore b/src/bin/pg_waldump/.gitignore
index ec51f41c76..e5089b322d 100644
--- a/src/bin/pg_waldump/.gitignore
+++ b/src/bin/pg_waldump/.gitignore
@@ -13,6 +13,7 @@
 /logicalmsgdesc.c
 /mxactdesc.c
 /nbtdesc.c
+/pgstatdesc.c
 /relmapdesc.c
 /replorigindesc.c
 /rmgrdesc_utils.c
diff --git a/src/bin/pg_waldump/rmgrdesc.c b/src/bin/pg_waldump/rmgrdesc.c
index 6b8c17bb4c..05b4f2acd1 100644
--- a/src/bin/pg_waldump/rmgrdesc.c
+++ b/src/bin/pg_waldump/rmgrdesc.c
@@ -30,6 +30,7 @@
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
+#include "utils/pgstat_xlog.h"
 #include "utils/relmapper.h"
 
 #define PG_RMGR(symname,name,redo,desc,identify,startup,cleanup,mask,decode) \
diff --git a/src/bin/pg_waldump/t/001_basic.pl b/src/bin/pg_waldump/t/001_basic.pl
index 578e473139..367ed6ab8c 100644
--- a/src/bin/pg_waldump/t/001_basic.pl
+++ b/src/bin/pg_waldump/t/001_basic.pl
@@ -73,7 +73,8 @@ BRIN
 CommitTs
 ReplicationOrigin
 Generic
-LogicalMessage$/,
+LogicalMessage
+PgStat$/,
 	'rmgr list');
 
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index e1c4f913f8..a5b1a2c998 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -4134,6 +4134,7 @@ xl_multixact_create
 xl_multixact_truncate
 xl_overwrite_contrecord
 xl_parameter_change
+xl_pgstat_data
 xl_relmap_update
 xl_replorigin_drop
 xl_replorigin_set
-- 
2.45.2

From 54537bbceab106b7a40aebdc815e6cd1ccd481cc Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 27 Dec 2024 12:05:33 +0900
Subject: [PATCH v2 4/4] injection_points: Add option and tests for WAL-logging

This serves as a template for WAL-logging related to pgstats, based on
the variable-numbered stats the module includes.  Some TAP tests are
added to check the backend facility.
---
 .../injection_points/injection_points.c       | 19 ++++++-
 .../injection_points/injection_stats.c        | 52 +++++++++++++++++++
 .../injection_points/injection_stats.h        |  3 +-
 .../modules/injection_points/t/001_stats.pl   | 22 ++++++++
 src/tools/pgindent/typedefs.list              |  1 +
 5 files changed, 95 insertions(+), 2 deletions(-)

diff --git a/src/test/modules/injection_points/injection_points.c b/src/test/modules/injection_points/injection_points.c
index 6bcde7b34e..a5180e97f5 100644
--- a/src/test/modules/injection_points/injection_points.c
+++ b/src/test/modules/injection_points/injection_points.c
@@ -104,7 +104,7 @@ extern PGDLLEXPORT void injection_wait(const char *name,
 static bool injection_point_local = false;
 
 /*
- * GUC variable
+ * GUC variables
  *
  * This GUC is useful to control if statistics should be enabled or not
  * during a test with injection points, like for example if a test relies
@@ -112,6 +112,12 @@ static bool injection_point_local = false;
  */
 bool		inj_stats_enabled = false;
 
+/*
+ * This GUC controls if statistics of injection points should be logged
+ * into WAL or not.
+ */
+bool		inj_stats_wal_enabled = false;
+
 /* Shared memory init callbacks */
 static shmem_request_hook_type prev_shmem_request_hook = NULL;
 static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
@@ -534,6 +540,17 @@ _PG_init(void)
 							 NULL,
 							 NULL);
 
+	DefineCustomBoolVariable("injection_points.log_stats",
+							 "Enables WAL-logging for injection points statistics.",
+							 NULL,
+							 &inj_stats_wal_enabled,
+							 false,
+							 PGC_POSTMASTER,
+							 0,
+							 NULL,
+							 NULL,
+							 NULL);
+
 	MarkGUCPrefixReserved("injection_points");
 
 	/* Shared memory initialization */
diff --git a/src/test/modules/injection_points/injection_stats.c b/src/test/modules/injection_points/injection_stats.c
index 21d5c10f39..c14655f70e 100644
--- a/src/test/modules/injection_points/injection_stats.c
+++ b/src/test/modules/injection_points/injection_stats.c
@@ -21,6 +21,7 @@
 #include "pgstat.h"
 #include "utils/builtins.h"
 #include "utils/pgstat_internal.h"
+#include "utils/pgstat_xlog.h"
 
 /* Structures for statistics of injection points */
 typedef struct PgStat_StatInjEntry
@@ -34,6 +35,14 @@ typedef struct PgStatShared_InjectionPoint
 	PgStat_StatInjEntry stats;
 } PgStatShared_InjectionPoint;
 
+/* Structure for data of injection points logged in WAL */
+typedef struct PgStat_StatInjRecord
+{
+	uint64		objid;			/* hash of the point name */
+	PgStat_StatInjEntry entry;	/* stats data */
+} PgStat_StatInjRecord;
+
+static void injection_stats_redo_cb(void *data, size_t data_size);
 static bool injection_stats_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
 
 static const PgStat_KindInfo injection_stats = {
@@ -48,6 +57,7 @@ static const PgStat_KindInfo injection_stats = {
 	.shared_data_off = offsetof(PgStatShared_InjectionPoint, stats),
 	.shared_data_len = sizeof(((PgStatShared_InjectionPoint *) 0)->stats),
 	.pending_size = sizeof(PgStat_StatInjEntry),
+	.redo_cb = injection_stats_redo_cb,
 	.flush_pending_cb = injection_stats_flush_cb,
 };
 
@@ -64,6 +74,31 @@ static const PgStat_KindInfo injection_stats = {
 /* Track if stats are loaded */
 static bool inj_stats_loaded = false;
 
+/*
+ * REDO callback for injection point stats.
+ */
+static void
+injection_stats_redo_cb(void *data, size_t data_size)
+{
+	PgStat_StatInjRecord *record_data = (PgStat_StatInjRecord *) data;
+	PgStat_StatInjEntry record_entry = record_data->entry;
+	PgStat_StatInjEntry *stat_entry;
+	PgStatShared_InjectionPoint *shstatent;
+	PgStat_EntryRef *entry_ref;
+
+	Assert(data_size == sizeof(PgStat_StatInjRecord));
+
+	/* create or fetch existing entry */
+	entry_ref = pgstat_prep_pending_entry(PGSTAT_KIND_INJECTION, InvalidOid,
+										  record_data->objid, NULL);
+
+	shstatent = (PgStatShared_InjectionPoint *) entry_ref->shared_stats;
+	stat_entry = &shstatent->stats;
+
+	/* Update the injection point statistics, overwriting any existing data */
+	*stat_entry = record_entry;
+}
+
 /*
  * Callback for stats handling
  */
@@ -72,6 +107,7 @@ injection_stats_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 {
 	PgStat_StatInjEntry *localent;
 	PgStatShared_InjectionPoint *shfuncent;
+	PgStat_StatInjRecord record_data = {0};
 
 	localent = (PgStat_StatInjEntry *) entry_ref->pending;
 	shfuncent = (PgStatShared_InjectionPoint *) entry_ref->shared_stats;
@@ -81,8 +117,24 @@ injection_stats_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 
 	shfuncent->stats.numcalls += localent->numcalls;
 
+	record_data.objid = entry_ref->shared_entry->key.objid;
+	record_data.entry = shfuncent->stats;
+
 	pgstat_unlock_entry(entry_ref);
 
+	/*
+	 * Store the data in WAL, if not in recovery and if the option is enabled.
+	 */
+	if (!RecoveryInProgress() && inj_stats_wal_enabled)
+	{
+		XLogRecPtr	lsn;
+
+		lsn = pgstat_xlog_data(PGSTAT_KIND_INJECTION, &record_data,
+							   sizeof(PgStat_StatInjRecord));
+
+		/* Force a flush, to ensure persistency */
+		XLogFlush(lsn);
+	}
 	return true;
 }
 
diff --git a/src/test/modules/injection_points/injection_stats.h b/src/test/modules/injection_points/injection_stats.h
index c48d533b4b..2583f3fe9c 100644
--- a/src/test/modules/injection_points/injection_stats.h
+++ b/src/test/modules/injection_points/injection_stats.h
@@ -15,8 +15,9 @@
 #ifndef INJECTION_STATS
 #define INJECTION_STATS
 
-/* GUC variable */
+/* GUC variables */
 extern bool inj_stats_enabled;
+extern bool inj_stats_wal_enabled;
 
 /* injection_stats.c */
 extern void pgstat_register_inj(void);
diff --git a/src/test/modules/injection_points/t/001_stats.pl b/src/test/modules/injection_points/t/001_stats.pl
index 36728f16fc..395c2e7cdb 100644
--- a/src/test/modules/injection_points/t/001_stats.pl
+++ b/src/test/modules/injection_points/t/001_stats.pl
@@ -75,4 +75,26 @@ $node->stop;
 $node->adjust_conf('postgresql.conf', 'shared_preload_libraries', "''");
 $node->start;
 
+# Stop the server and enable WAL, the stats are preserved after recovery.
+$node->stop;
+$node->append_conf(
+	'postgresql.conf', qq(
+shared_preload_libraries = 'injection_points'
+injection_points.log_stats = true
+));
+$node->start;
+
+# Two calls, both WAL-logged.
+$node->safe_psql('postgres',
+	"SELECT injection_points_attach('stats-wal-notice', 'notice');");
+$node->safe_psql('postgres',
+	"SELECT injection_points_run('stats-wal-notice');");
+$node->safe_psql('postgres',
+	"SELECT injection_points_run('stats-wal-notice');");
+$node->stop('immediate');
+$node->start;
+$numcalls = $node->safe_psql('postgres',
+	"SELECT injection_points_stats_numcalls('stats-wal-notice');");
+is($numcalls, '2', 'number of stats after crash with WAL-logging enabled');
+
 done_testing();
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index a5b1a2c998..47e3e07f5e 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2166,6 +2166,7 @@ PgStat_StatDBEntry
 PgStat_StatFuncEntry
 PgStat_StatInjEntry
 PgStat_StatInjFixedEntry
+PgStat_StatInjRecord
 PgStat_StatReplSlotEntry
 PgStat_StatSubEntry
 PgStat_StatTabEntry
-- 
2.45.2

From f5eb1b66f1883d2b2e23dfb20eedf8328b0a01f3 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 10 Jan 2025 13:18:27 +0900
Subject: [PATCH v3 2/4] Move information about pgstats kinds into its own
 header

This information is split into its own header as it will be used by a
follow-up patch, to be used in some frontend and backend code.
---
 src/include/pgstat.h            | 57 +-------------------------
 src/include/utils/pgstat_kind.h | 72 +++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+), 56 deletions(-)
 create mode 100644 src/include/utils/pgstat_kind.h

diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 6475889c58..81ad8e2b43 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -18,6 +18,7 @@
 #include "replication/conflict.h"
 #include "utils/backend_progress.h" /* for backward compatibility */
 #include "utils/backend_status.h"	/* for backward compatibility */
+#include "utils/pgstat_kind.h"
 #include "utils/relcache.h"
 #include "utils/wait_event.h"	/* for backward compatibility */
 
@@ -33,62 +34,6 @@
 /* Default directory to store temporary statistics data in */
 #define PG_STAT_TMP_DIR		"pg_stat_tmp"
 
-/* The types of statistics entries */
-#define PgStat_Kind uint32
-
-/* Range of IDs allowed, for built-in and custom kinds */
-#define PGSTAT_KIND_MIN	1		/* Minimum ID allowed */
-#define PGSTAT_KIND_MAX	256		/* Maximum ID allowed */
-
-/* use 0 for INVALID, to catch zero-initialized data */
-#define PGSTAT_KIND_INVALID 0
-
-/* stats for variable-numbered objects */
-#define PGSTAT_KIND_DATABASE	1	/* database-wide statistics */
-#define PGSTAT_KIND_RELATION	2	/* per-table statistics */
-#define PGSTAT_KIND_FUNCTION	3	/* per-function statistics */
-#define PGSTAT_KIND_REPLSLOT	4	/* per-slot statistics */
-#define PGSTAT_KIND_SUBSCRIPTION	5	/* per-subscription statistics */
-#define PGSTAT_KIND_BACKEND	6	/* per-backend statistics */
-
-/* stats for fixed-numbered objects */
-#define PGSTAT_KIND_ARCHIVER	7
-#define PGSTAT_KIND_BGWRITER	8
-#define PGSTAT_KIND_CHECKPOINTER	9
-#define PGSTAT_KIND_IO	10
-#define PGSTAT_KIND_SLRU	11
-#define PGSTAT_KIND_WAL	12
-
-#define PGSTAT_KIND_BUILTIN_MIN PGSTAT_KIND_DATABASE
-#define PGSTAT_KIND_BUILTIN_MAX PGSTAT_KIND_WAL
-#define PGSTAT_KIND_BUILTIN_SIZE (PGSTAT_KIND_BUILTIN_MAX + 1)
-
-/* Custom stats kinds */
-
-/* Range of IDs allowed for custom stats kinds */
-#define PGSTAT_KIND_CUSTOM_MIN	128
-#define PGSTAT_KIND_CUSTOM_MAX	PGSTAT_KIND_MAX
-#define PGSTAT_KIND_CUSTOM_SIZE	(PGSTAT_KIND_CUSTOM_MAX - PGSTAT_KIND_CUSTOM_MIN + 1)
-
-/*
- * PgStat_Kind to use for extensions that require an ID, but are still in
- * development and have not reserved their own unique kind ID yet. See:
- * https://wiki.postgresql.org/wiki/CustomCumulativeStats
- */
-#define PGSTAT_KIND_EXPERIMENTAL	128
-
-static inline bool
-pgstat_is_kind_builtin(PgStat_Kind kind)
-{
-	return kind >= PGSTAT_KIND_BUILTIN_MIN && kind <= PGSTAT_KIND_BUILTIN_MAX;
-}
-
-static inline bool
-pgstat_is_kind_custom(PgStat_Kind kind)
-{
-	return kind >= PGSTAT_KIND_CUSTOM_MIN && kind <= PGSTAT_KIND_CUSTOM_MAX;
-}
-
 /* Values for track_functions GUC variable --- order is significant! */
 typedef enum TrackFunctionsLevel
 {
diff --git a/src/include/utils/pgstat_kind.h b/src/include/utils/pgstat_kind.h
new file mode 100644
index 0000000000..f44169fd5a
--- /dev/null
+++ b/src/include/utils/pgstat_kind.h
@@ -0,0 +1,72 @@
+/* ----------
+ *	pgstat_kind.h
+ *
+ *	Definitions related to the statistics kinds for the PostgreSQL
+ *	cumulative statistics system.  Can be included in backend or
+ *	frontend code.
+ *
+ *	Copyright (c) 2001-2025, PostgreSQL Global Development Group
+ *
+ *	src/include/utils/pgstat_kind.h
+ * ----------
+ */
+#ifndef PGSTAT_KIND_H
+#define PGSTAT_KIND_H
+
+/* The types of statistics entries */
+#define PgStat_Kind uint32
+
+/* Range of IDs allowed, for built-in and custom kinds */
+#define PGSTAT_KIND_MIN	1		/* Minimum ID allowed */
+#define PGSTAT_KIND_MAX	256		/* Maximum ID allowed */
+
+/* use 0 for INVALID, to catch zero-initialized data */
+#define PGSTAT_KIND_INVALID 0
+
+/* stats for variable-numbered objects */
+#define PGSTAT_KIND_DATABASE	1	/* database-wide statistics */
+#define PGSTAT_KIND_RELATION	2	/* per-table statistics */
+#define PGSTAT_KIND_FUNCTION	3	/* per-function statistics */
+#define PGSTAT_KIND_REPLSLOT	4	/* per-slot statistics */
+#define PGSTAT_KIND_SUBSCRIPTION	5	/* per-subscription statistics */
+#define PGSTAT_KIND_BACKEND	6	/* per-backend statistics */
+
+/* stats for fixed-numbered objects */
+#define PGSTAT_KIND_ARCHIVER	7
+#define PGSTAT_KIND_BGWRITER	8
+#define PGSTAT_KIND_CHECKPOINTER	9
+#define PGSTAT_KIND_IO	10
+#define PGSTAT_KIND_SLRU	11
+#define PGSTAT_KIND_WAL	12
+
+#define PGSTAT_KIND_BUILTIN_MIN PGSTAT_KIND_DATABASE
+#define PGSTAT_KIND_BUILTIN_MAX PGSTAT_KIND_WAL
+#define PGSTAT_KIND_BUILTIN_SIZE (PGSTAT_KIND_BUILTIN_MAX + 1)
+
+/* Custom stats kinds */
+
+/* Range of IDs allowed for custom stats kinds */
+#define PGSTAT_KIND_CUSTOM_MIN	128
+#define PGSTAT_KIND_CUSTOM_MAX	PGSTAT_KIND_MAX
+#define PGSTAT_KIND_CUSTOM_SIZE	(PGSTAT_KIND_CUSTOM_MAX - PGSTAT_KIND_CUSTOM_MIN + 1)
+
+/*
+ * PgStat_Kind to use for extensions that require an ID, but are still in
+ * development and have not reserved their own unique kind ID yet. See:
+ * https://wiki.postgresql.org/wiki/CustomCumulativeStats
+ */
+#define PGSTAT_KIND_EXPERIMENTAL	128
+
+static inline bool
+pgstat_is_kind_builtin(PgStat_Kind kind)
+{
+	return kind >= PGSTAT_KIND_BUILTIN_MIN && kind <= PGSTAT_KIND_BUILTIN_MAX;
+}
+
+static inline bool
+pgstat_is_kind_custom(PgStat_Kind kind)
+{
+	return kind >= PGSTAT_KIND_CUSTOM_MIN && kind <= PGSTAT_KIND_CUSTOM_MAX;
+}
+
+#endif							/* PGSTAT_KIND_H */
-- 
2.47.1

From a67dcb96c093c427e6b7fb1eeb906e2d05c3796a Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 10 Jan 2025 13:26:46 +0900
Subject: [PATCH v3 3/4] Add RMGR and WAL-logging API for pgstats

This commit adds a new facility in the backend that offers to pgstats
kinds the possibility to WAL-log data that need to be persisted across
restarts:
- A new callback called redo_cb can be defined by a pgstats_kind.
- pgstat_xlog.c includes one API able to register some payload data and
its size.  Stats kinds doing WAL-logging require a definition of
redo_cb.
- pg_waldump is able to show the data logged, as hexadedimal data.

This facility has applications for in-core and custom stats kinds, with
one primary case being the possibility to WAL-log some statistics
related to relations so as these are not lost post-crash.  This is left
as future work.
---
 src/include/access/rmgrlist.h            |  1 +
 src/include/utils/pgstat_internal.h      |  8 +++
 src/include/utils/pgstat_xlog.h          | 41 ++++++++++++++
 src/backend/access/rmgrdesc/Makefile     |  1 +
 src/backend/access/rmgrdesc/meson.build  |  1 +
 src/backend/access/rmgrdesc/pgstatdesc.c | 49 ++++++++++++++++
 src/backend/access/transam/rmgr.c        |  1 +
 src/backend/utils/activity/Makefile      |  1 +
 src/backend/utils/activity/meson.build   |  1 +
 src/backend/utils/activity/pgstat_xlog.c | 72 ++++++++++++++++++++++++
 src/bin/pg_waldump/.gitignore            |  1 +
 src/bin/pg_waldump/rmgrdesc.c            |  1 +
 src/bin/pg_waldump/t/001_basic.pl        |  3 +-
 src/tools/pgindent/typedefs.list         |  1 +
 14 files changed, 181 insertions(+), 1 deletion(-)
 create mode 100644 src/include/utils/pgstat_xlog.h
 create mode 100644 src/backend/access/rmgrdesc/pgstatdesc.c
 create mode 100644 src/backend/utils/activity/pgstat_xlog.c

diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index 8e7fc9db87..409397cb21 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -47,3 +47,4 @@ PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_i
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL, NULL, NULL)
 PG_RMGR(RM_GENERIC_ID, "Generic", generic_redo, generic_desc, generic_identify, NULL, NULL, generic_mask, NULL)
 PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL, NULL, logicalmsg_decode)
+PG_RMGR(RM_PGSTAT_ID, "PgStat", pgstat_redo, pgstat_desc, pgstat_identify, NULL, NULL, NULL, NULL)
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 4bb8e5c53a..7a87d4e2f6 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -258,6 +258,14 @@ typedef struct PgStat_KindInfo
 	 */
 	void		(*init_backend_cb) (void);
 
+	/*
+	 * Perform custom actions when replaying WAL related to a statistics kind.
+	 *
+	 * "data" is a pointer to the stats information that can be used by the
+	 * stats kind at redo.
+	 */
+	void		(*redo_cb) (void *data, size_t data_size);
+
 	/*
 	 * For variable-numbered stats: flush pending stats. Required if pending
 	 * data is used.  See flush_fixed_cb for fixed-numbered stats.
diff --git a/src/include/utils/pgstat_xlog.h b/src/include/utils/pgstat_xlog.h
new file mode 100644
index 0000000000..8e229b4f12
--- /dev/null
+++ b/src/include/utils/pgstat_xlog.h
@@ -0,0 +1,41 @@
+/* ----------
+ * pgstat_xlog.h
+ *	  Exports from utils/activity/pgstat_xlog.c
+ *
+ * Copyright (c) 2001-2025, PostgreSQL Global Development Group
+ *
+ * src/include/utils/pgstat_xlog.h
+ * ----------
+ */
+#ifndef PGSTAT_XLOG_H
+#define PGSTAT_XLOG_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+#include "utils/pgstat_kind.h"
+
+/*
+ * Generic WAL record for pgstat data.
+ */
+typedef struct xl_pgstat_data
+{
+	PgStat_Kind stats_kind;
+	size_t		data_size;		/* size of the data */
+	/* stats data, worth data_size */
+	char		data[FLEXIBLE_ARRAY_MEMBER];
+} xl_pgstat_data;
+
+#define SizeOfPgStatData    (offsetof(xl_pgstat_data, data))
+
+extern XLogRecPtr pgstat_xlog_data(PgStat_Kind stats_kind,
+								   const void *data,
+								   size_t data_size);
+
+/* RMGR API */
+#define XLOG_PGSTAT_DATA	0x00
+extern void pgstat_redo(XLogReaderState *record);
+extern void pgstat_desc(StringInfo buf, XLogReaderState *record);
+extern const char *pgstat_identify(uint8 info);
+
+#endif							/* PGSTAT_XLOG_H */
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index cd95eec37f..3979d22946 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -21,6 +21,7 @@ OBJS = \
 	logicalmsgdesc.o \
 	mxactdesc.o \
 	nbtdesc.o \
+	pgstatdesc.o \
 	relmapdesc.o \
 	replorigindesc.o \
 	rmgrdesc_utils.o \
diff --git a/src/backend/access/rmgrdesc/meson.build b/src/backend/access/rmgrdesc/meson.build
index 96c98e800c..91c53e634c 100644
--- a/src/backend/access/rmgrdesc/meson.build
+++ b/src/backend/access/rmgrdesc/meson.build
@@ -14,6 +14,7 @@ rmgr_desc_sources = files(
   'logicalmsgdesc.c',
   'mxactdesc.c',
   'nbtdesc.c',
+  'pgstatdesc.c',
   'relmapdesc.c',
   'replorigindesc.c',
   'rmgrdesc_utils.c',
diff --git a/src/backend/access/rmgrdesc/pgstatdesc.c b/src/backend/access/rmgrdesc/pgstatdesc.c
new file mode 100644
index 0000000000..233f9f1994
--- /dev/null
+++ b/src/backend/access/rmgrdesc/pgstatdesc.c
@@ -0,0 +1,49 @@
+/*-------------------------------------------------------------------------
+ *
+ * pgstatdesc.c
+ *	  rmgr descriptor routines for utils/activity/pgstat_xlog.c
+ *
+ * Portions Copyright (c) 2001-2025, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/pgstatdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "utils/pgstat_xlog.h"
+
+void
+pgstat_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_PGSTAT_DATA)
+	{
+		xl_pgstat_data *xlrec = (xl_pgstat_data *) rec;
+		char	   *sep = "";
+
+		appendStringInfo(buf, "stats kind \"%u\"; with data (%zu bytes): ",
+						 xlrec->stats_kind, xlrec->data_size);
+
+		/* Write stats data as a series of hex bytes */
+		for (int cnt = 0; cnt < xlrec->data_size; cnt++)
+		{
+			appendStringInfo(buf, "%s%02X", sep, (unsigned char) xlrec->data[cnt]);
+			sep = " ";
+		}
+	}
+}
+
+const char *
+pgstat_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_PGSTAT_DATA)
+		return "PGSTAT_DATA";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 1b7499726e..945843a78e 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -39,6 +39,7 @@
 #include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
+#include "utils/pgstat_xlog.h"
 #include "utils/relmapper.h"
 /* IWYU pragma: end_keep */
 
diff --git a/src/backend/utils/activity/Makefile b/src/backend/utils/activity/Makefile
index 9c2443e1ec..fdbdd6bfe6 100644
--- a/src/backend/utils/activity/Makefile
+++ b/src/backend/utils/activity/Makefile
@@ -33,6 +33,7 @@ OBJS = \
 	pgstat_subscription.o \
 	pgstat_wal.o \
 	pgstat_xact.o \
+	pgstat_xlog.o \
 	wait_event.o \
 	wait_event_funcs.o
 
diff --git a/src/backend/utils/activity/meson.build b/src/backend/utils/activity/meson.build
index d8e56b49c2..533efef2cb 100644
--- a/src/backend/utils/activity/meson.build
+++ b/src/backend/utils/activity/meson.build
@@ -18,6 +18,7 @@ backend_sources += files(
   'pgstat_subscription.c',
   'pgstat_wal.c',
   'pgstat_xact.c',
+  'pgstat_xlog.c',
 )
 
 # this includes a .c file with contents generated in ../../../include/activity,
diff --git a/src/backend/utils/activity/pgstat_xlog.c b/src/backend/utils/activity/pgstat_xlog.c
new file mode 100644
index 0000000000..59a06cd9e1
--- /dev/null
+++ b/src/backend/utils/activity/pgstat_xlog.c
@@ -0,0 +1,72 @@
+/* ----------
+ * pgstat_xlog.c
+ *	   WAL replay logic for cumulative statistics.
+ *
+ *
+ * Copyright (c) 2001-2025, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/activity/pgstat_xlog.c
+ * ----------
+ */
+
+#include "postgres.h"
+
+#include <unistd.h>
+
+#include "access/xlog.h"
+#include "access/xloginsert.h"
+#include "utils/pgstat_internal.h"
+#include "utils/pgstat_xlog.h"
+
+/*
+ * Write pgstats record data into WAL.
+ */
+XLogRecPtr
+pgstat_xlog_data(PgStat_Kind stats_kind, const void *data,
+				 size_t data_size)
+{
+	xl_pgstat_data xlrec;
+	XLogRecPtr	lsn;
+
+	xlrec.stats_kind = stats_kind;
+	xlrec.data_size = data_size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfPgStatData);
+	XLogRegisterData(data, data_size);
+
+	lsn = XLogInsert(RM_PGSTAT_ID, XLOG_PGSTAT_DATA);
+	return lsn;
+}
+
+/*
+ * Redo just passes down to the stats kind expected by this record
+ * data included in it.
+ */
+void
+pgstat_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+	xl_pgstat_data *xlrec;
+	PgStat_Kind stats_kind;
+	const PgStat_KindInfo *kind_info;
+
+	if (info != XLOG_PGSTAT_DATA)
+		elog(PANIC, "pgstat_redo: unknown op code %u", info);
+
+	xlrec = (xl_pgstat_data *) XLogRecGetData(record);
+
+	stats_kind = xlrec->stats_kind;
+	kind_info = pgstat_get_kind_info(stats_kind);
+
+	if (kind_info == NULL)
+		elog(FATAL, "pgstat_redo: invalid stats kind found: kind=%u",
+			 stats_kind);
+
+	if (kind_info->redo_cb == NULL)
+		elog(FATAL, "pgstat_redo: no redo callback found: kind=%s",
+			 kind_info->name);
+
+	kind_info->redo_cb(xlrec->data, xlrec->data_size);
+}
diff --git a/src/bin/pg_waldump/.gitignore b/src/bin/pg_waldump/.gitignore
index ec51f41c76..e5089b322d 100644
--- a/src/bin/pg_waldump/.gitignore
+++ b/src/bin/pg_waldump/.gitignore
@@ -13,6 +13,7 @@
 /logicalmsgdesc.c
 /mxactdesc.c
 /nbtdesc.c
+/pgstatdesc.c
 /relmapdesc.c
 /replorigindesc.c
 /rmgrdesc_utils.c
diff --git a/src/bin/pg_waldump/rmgrdesc.c b/src/bin/pg_waldump/rmgrdesc.c
index 6b8c17bb4c..05b4f2acd1 100644
--- a/src/bin/pg_waldump/rmgrdesc.c
+++ b/src/bin/pg_waldump/rmgrdesc.c
@@ -30,6 +30,7 @@
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
+#include "utils/pgstat_xlog.h"
 #include "utils/relmapper.h"
 
 #define PG_RMGR(symname,name,redo,desc,identify,startup,cleanup,mask,decode) \
diff --git a/src/bin/pg_waldump/t/001_basic.pl b/src/bin/pg_waldump/t/001_basic.pl
index 8d574a410c..70256ecccb 100644
--- a/src/bin/pg_waldump/t/001_basic.pl
+++ b/src/bin/pg_waldump/t/001_basic.pl
@@ -73,7 +73,8 @@ BRIN
 CommitTs
 ReplicationOrigin
 Generic
-LogicalMessage$/,
+LogicalMessage
+PgStat$/,
 	'rmgr list');
 
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index eb93debe10..4db1e7cf4b 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -4135,6 +4135,7 @@ xl_multixact_create
 xl_multixact_truncate
 xl_overwrite_contrecord
 xl_parameter_change
+xl_pgstat_data
 xl_relmap_update
 xl_replorigin_drop
 xl_replorigin_set
-- 
2.47.1

From 00f4bc416b214b5d2f7d53ed5eedbd1209f43953 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 10 Jan 2025 13:36:28 +0900
Subject: [PATCH v3 4/4] injection_points: Add option and tests for WAL-logging

This serves as a template for WAL-logging related to pgstats, based on
the variable-numbered stats the module includes.  Some TAP tests are
added to check the backend facility.
---
 .../injection_points/injection_points.c       | 19 ++++++-
 .../injection_points/injection_stats.c        | 54 +++++++++++++++++++
 .../injection_points/injection_stats.h        |  3 +-
 .../modules/injection_points/t/001_stats.pl   | 22 ++++++++
 src/tools/pgindent/typedefs.list              |  1 +
 5 files changed, 97 insertions(+), 2 deletions(-)

diff --git a/src/test/modules/injection_points/injection_points.c b/src/test/modules/injection_points/injection_points.c
index ad528d7775..c7f0d6d242 100644
--- a/src/test/modules/injection_points/injection_points.c
+++ b/src/test/modules/injection_points/injection_points.c
@@ -104,7 +104,7 @@ extern PGDLLEXPORT void injection_wait(const char *name,
 static bool injection_point_local = false;
 
 /*
- * GUC variable
+ * GUC variables
  *
  * This GUC is useful to control if statistics should be enabled or not
  * during a test with injection points, like for example if a test relies
@@ -112,6 +112,12 @@ static bool injection_point_local = false;
  */
 bool		inj_stats_enabled = false;
 
+/*
+ * This GUC controls if statistics of injection points should be logged
+ * into WAL or not.
+ */
+bool		inj_stats_wal_enabled = false;
+
 /* Shared memory init callbacks */
 static shmem_request_hook_type prev_shmem_request_hook = NULL;
 static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
@@ -534,6 +540,17 @@ _PG_init(void)
 							 NULL,
 							 NULL);
 
+	DefineCustomBoolVariable("injection_points.log_stats",
+							 "Enables WAL-logging for injection points statistics.",
+							 NULL,
+							 &inj_stats_wal_enabled,
+							 false,
+							 PGC_POSTMASTER,
+							 0,
+							 NULL,
+							 NULL,
+							 NULL);
+
 	MarkGUCPrefixReserved("injection_points");
 
 	/* Shared memory initialization */
diff --git a/src/test/modules/injection_points/injection_stats.c b/src/test/modules/injection_points/injection_stats.c
index 5db62bca66..df52cb026e 100644
--- a/src/test/modules/injection_points/injection_stats.c
+++ b/src/test/modules/injection_points/injection_stats.c
@@ -21,6 +21,7 @@
 #include "pgstat.h"
 #include "utils/builtins.h"
 #include "utils/pgstat_internal.h"
+#include "utils/pgstat_xlog.h"
 
 /* Structures for statistics of injection points */
 typedef struct PgStat_StatInjEntry
@@ -34,6 +35,14 @@ typedef struct PgStatShared_InjectionPoint
 	PgStat_StatInjEntry stats;
 } PgStatShared_InjectionPoint;
 
+/* Structure for data of injection points logged in WAL */
+typedef struct PgStat_StatInjRecord
+{
+	uint64		objid;			/* hash of the point name */
+	PgStat_StatInjEntry entry;	/* stats data */
+} PgStat_StatInjRecord;
+
+static void injection_stats_redo_cb(void *data, size_t data_size);
 static bool injection_stats_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
 
 static const PgStat_KindInfo injection_stats = {
@@ -48,6 +57,7 @@ static const PgStat_KindInfo injection_stats = {
 	.shared_data_off = offsetof(PgStatShared_InjectionPoint, stats),
 	.shared_data_len = sizeof(((PgStatShared_InjectionPoint *) 0)->stats),
 	.pending_size = sizeof(PgStat_StatInjEntry),
+	.redo_cb = injection_stats_redo_cb,
 	.flush_pending_cb = injection_stats_flush_cb,
 };
 
@@ -64,6 +74,31 @@ static const PgStat_KindInfo injection_stats = {
 /* Track if stats are loaded */
 static bool inj_stats_loaded = false;
 
+/*
+ * REDO callback for injection point stats.
+ */
+static void
+injection_stats_redo_cb(void *data, size_t data_size)
+{
+	PgStat_StatInjRecord *record_data = (PgStat_StatInjRecord *) data;
+	PgStat_StatInjEntry record_entry = record_data->entry;
+	PgStat_StatInjEntry *stat_entry;
+	PgStatShared_InjectionPoint *shstatent;
+	PgStat_EntryRef *entry_ref;
+
+	Assert(data_size == sizeof(PgStat_StatInjRecord));
+
+	/* create or fetch existing entry */
+	entry_ref = pgstat_prep_pending_entry(PGSTAT_KIND_INJECTION, InvalidOid,
+										  record_data->objid, NULL);
+
+	shstatent = (PgStatShared_InjectionPoint *) entry_ref->shared_stats;
+	stat_entry = &shstatent->stats;
+
+	/* Update the injection point statistics, overwriting any existing data */
+	*stat_entry = record_entry;
+}
+
 /*
  * Callback for stats handling
  */
@@ -72,6 +107,9 @@ injection_stats_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 {
 	PgStat_StatInjEntry *localent;
 	PgStatShared_InjectionPoint *shfuncent;
+	PgStat_StatInjRecord record_data;
+
+	memset(&record_data, 0, sizeof(PgStat_StatInjRecord));
 
 	localent = (PgStat_StatInjEntry *) entry_ref->pending;
 	shfuncent = (PgStatShared_InjectionPoint *) entry_ref->shared_stats;
@@ -81,8 +119,24 @@ injection_stats_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 
 	shfuncent->stats.numcalls += localent->numcalls;
 
+	record_data.objid = entry_ref->shared_entry->key.objid;
+	record_data.entry = shfuncent->stats;
+
 	pgstat_unlock_entry(entry_ref);
 
+	/*
+	 * Store the data in WAL, if not in recovery and if the option is enabled.
+	 */
+	if (!RecoveryInProgress() && inj_stats_wal_enabled)
+	{
+		XLogRecPtr	lsn;
+
+		lsn = pgstat_xlog_data(PGSTAT_KIND_INJECTION, &record_data,
+							   sizeof(PgStat_StatInjRecord));
+
+		/* Force a flush, to ensure persistency */
+		XLogFlush(lsn);
+	}
 	return true;
 }
 
diff --git a/src/test/modules/injection_points/injection_stats.h b/src/test/modules/injection_points/injection_stats.h
index ba310c52c7..baa8bb506c 100644
--- a/src/test/modules/injection_points/injection_stats.h
+++ b/src/test/modules/injection_points/injection_stats.h
@@ -15,8 +15,9 @@
 #ifndef INJECTION_STATS
 #define INJECTION_STATS
 
-/* GUC variable */
+/* GUC variables */
 extern bool inj_stats_enabled;
+extern bool inj_stats_wal_enabled;
 
 /* injection_stats.c */
 extern void pgstat_register_inj(void);
diff --git a/src/test/modules/injection_points/t/001_stats.pl b/src/test/modules/injection_points/t/001_stats.pl
index d4539fe872..4b34dd0a5a 100644
--- a/src/test/modules/injection_points/t/001_stats.pl
+++ b/src/test/modules/injection_points/t/001_stats.pl
@@ -75,4 +75,26 @@ $node->stop;
 $node->adjust_conf('postgresql.conf', 'shared_preload_libraries', "''");
 $node->start;
 
+# Stop the server and enable WAL, the stats are preserved after recovery.
+$node->stop;
+$node->append_conf(
+	'postgresql.conf', qq(
+shared_preload_libraries = 'injection_points'
+injection_points.log_stats = true
+));
+$node->start;
+
+# Two calls, both WAL-logged.
+$node->safe_psql('postgres',
+	"SELECT injection_points_attach('stats-wal-notice', 'notice');");
+$node->safe_psql('postgres',
+	"SELECT injection_points_run('stats-wal-notice');");
+$node->safe_psql('postgres',
+	"SELECT injection_points_run('stats-wal-notice');");
+$node->stop('immediate');
+$node->start;
+$numcalls = $node->safe_psql('postgres',
+	"SELECT injection_points_stats_numcalls('stats-wal-notice');");
+is($numcalls, '2', 'number of stats after crash with WAL-logging enabled');
+
 done_testing();
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 4db1e7cf4b..303a06b3fb 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2167,6 +2167,7 @@ PgStat_StatDBEntry
 PgStat_StatFuncEntry
 PgStat_StatInjEntry
 PgStat_StatInjFixedEntry
+PgStat_StatInjRecord
 PgStat_StatReplSlotEntry
 PgStat_StatSubEntry
 PgStat_StatTabEntry
-- 
2.47.1

From 7d4aa6fc0e348065b46c31cbb21d7a4d2f21e5b2 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 10 Jan 2025 13:26:46 +0900
Subject: [PATCH v3 3/4] Add RMGR and WAL-logging API for pgstats

This commit adds a new facility in the backend that offers to pgstats
kinds the possibility to WAL-log data that need to be persisted across
restarts:
- A new callback called redo_cb can be defined by a pgstats_kind.
- pgstat_xlog.c includes one API able to register some payload data and
its size.  Stats kinds doing WAL-logging require a definition of
redo_cb.
- pg_waldump is able to show the data logged, as hexadedimal data.

This facility has applications for in-core and custom stats kinds, with
one primary case being the possibility to WAL-log some statistics
related to relations so as these are not lost post-crash.  This is left
as future work.
---
 src/include/access/rmgrlist.h            |  1 +
 src/include/utils/pgstat_internal.h      |  8 +++
 src/include/utils/pgstat_xlog.h          | 41 ++++++++++++++
 src/backend/access/rmgrdesc/Makefile     |  1 +
 src/backend/access/rmgrdesc/meson.build  |  1 +
 src/backend/access/rmgrdesc/pgstatdesc.c | 49 ++++++++++++++++
 src/backend/access/transam/rmgr.c        |  1 +
 src/backend/utils/activity/Makefile      |  1 +
 src/backend/utils/activity/meson.build   |  1 +
 src/backend/utils/activity/pgstat_xlog.c | 72 ++++++++++++++++++++++++
 src/bin/pg_waldump/.gitignore            |  1 +
 src/bin/pg_waldump/rmgrdesc.c            |  1 +
 src/bin/pg_waldump/t/001_basic.pl        |  3 +-
 src/tools/pgindent/typedefs.list         |  1 +
 14 files changed, 181 insertions(+), 1 deletion(-)
 create mode 100644 src/include/utils/pgstat_xlog.h
 create mode 100644 src/backend/access/rmgrdesc/pgstatdesc.c
 create mode 100644 src/backend/utils/activity/pgstat_xlog.c

diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index 8e7fc9db87..409397cb21 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -47,3 +47,4 @@ PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_i
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL, NULL, NULL)
 PG_RMGR(RM_GENERIC_ID, "Generic", generic_redo, generic_desc, generic_identify, NULL, NULL, generic_mask, NULL)
 PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL, NULL, logicalmsg_decode)
+PG_RMGR(RM_PGSTAT_ID, "PgStat", pgstat_redo, pgstat_desc, pgstat_identify, NULL, NULL, NULL, NULL)
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 4bb8e5c53a..7a87d4e2f6 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -258,6 +258,14 @@ typedef struct PgStat_KindInfo
 	 */
 	void		(*init_backend_cb) (void);
 
+	/*
+	 * Perform custom actions when replaying WAL related to a statistics kind.
+	 *
+	 * "data" is a pointer to the stats information that can be used by the
+	 * stats kind at redo.
+	 */
+	void		(*redo_cb) (void *data, size_t data_size);
+
 	/*
 	 * For variable-numbered stats: flush pending stats. Required if pending
 	 * data is used.  See flush_fixed_cb for fixed-numbered stats.
diff --git a/src/include/utils/pgstat_xlog.h b/src/include/utils/pgstat_xlog.h
new file mode 100644
index 0000000000..8e229b4f12
--- /dev/null
+++ b/src/include/utils/pgstat_xlog.h
@@ -0,0 +1,41 @@
+/* ----------
+ * pgstat_xlog.h
+ *	  Exports from utils/activity/pgstat_xlog.c
+ *
+ * Copyright (c) 2001-2025, PostgreSQL Global Development Group
+ *
+ * src/include/utils/pgstat_xlog.h
+ * ----------
+ */
+#ifndef PGSTAT_XLOG_H
+#define PGSTAT_XLOG_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+#include "utils/pgstat_kind.h"
+
+/*
+ * Generic WAL record for pgstat data.
+ */
+typedef struct xl_pgstat_data
+{
+	PgStat_Kind stats_kind;
+	size_t		data_size;		/* size of the data */
+	/* stats data, worth data_size */
+	char		data[FLEXIBLE_ARRAY_MEMBER];
+} xl_pgstat_data;
+
+#define SizeOfPgStatData    (offsetof(xl_pgstat_data, data))
+
+extern XLogRecPtr pgstat_xlog_data(PgStat_Kind stats_kind,
+								   const void *data,
+								   size_t data_size);
+
+/* RMGR API */
+#define XLOG_PGSTAT_DATA	0x00
+extern void pgstat_redo(XLogReaderState *record);
+extern void pgstat_desc(StringInfo buf, XLogReaderState *record);
+extern const char *pgstat_identify(uint8 info);
+
+#endif							/* PGSTAT_XLOG_H */
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index cd95eec37f..3979d22946 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -21,6 +21,7 @@ OBJS = \
 	logicalmsgdesc.o \
 	mxactdesc.o \
 	nbtdesc.o \
+	pgstatdesc.o \
 	relmapdesc.o \
 	replorigindesc.o \
 	rmgrdesc_utils.o \
diff --git a/src/backend/access/rmgrdesc/meson.build b/src/backend/access/rmgrdesc/meson.build
index 96c98e800c..91c53e634c 100644
--- a/src/backend/access/rmgrdesc/meson.build
+++ b/src/backend/access/rmgrdesc/meson.build
@@ -14,6 +14,7 @@ rmgr_desc_sources = files(
   'logicalmsgdesc.c',
   'mxactdesc.c',
   'nbtdesc.c',
+  'pgstatdesc.c',
   'relmapdesc.c',
   'replorigindesc.c',
   'rmgrdesc_utils.c',
diff --git a/src/backend/access/rmgrdesc/pgstatdesc.c b/src/backend/access/rmgrdesc/pgstatdesc.c
new file mode 100644
index 0000000000..233f9f1994
--- /dev/null
+++ b/src/backend/access/rmgrdesc/pgstatdesc.c
@@ -0,0 +1,49 @@
+/*-------------------------------------------------------------------------
+ *
+ * pgstatdesc.c
+ *	  rmgr descriptor routines for utils/activity/pgstat_xlog.c
+ *
+ * Portions Copyright (c) 2001-2025, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/pgstatdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "utils/pgstat_xlog.h"
+
+void
+pgstat_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_PGSTAT_DATA)
+	{
+		xl_pgstat_data *xlrec = (xl_pgstat_data *) rec;
+		char	   *sep = "";
+
+		appendStringInfo(buf, "stats kind \"%u\"; with data (%zu bytes): ",
+						 xlrec->stats_kind, xlrec->data_size);
+
+		/* Write stats data as a series of hex bytes */
+		for (int cnt = 0; cnt < xlrec->data_size; cnt++)
+		{
+			appendStringInfo(buf, "%s%02X", sep, (unsigned char) xlrec->data[cnt]);
+			sep = " ";
+		}
+	}
+}
+
+const char *
+pgstat_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_PGSTAT_DATA)
+		return "PGSTAT_DATA";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 1b7499726e..945843a78e 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -39,6 +39,7 @@
 #include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
+#include "utils/pgstat_xlog.h"
 #include "utils/relmapper.h"
 /* IWYU pragma: end_keep */
 
diff --git a/src/backend/utils/activity/Makefile b/src/backend/utils/activity/Makefile
index 9c2443e1ec..fdbdd6bfe6 100644
--- a/src/backend/utils/activity/Makefile
+++ b/src/backend/utils/activity/Makefile
@@ -33,6 +33,7 @@ OBJS = \
 	pgstat_subscription.o \
 	pgstat_wal.o \
 	pgstat_xact.o \
+	pgstat_xlog.o \
 	wait_event.o \
 	wait_event_funcs.o
 
diff --git a/src/backend/utils/activity/meson.build b/src/backend/utils/activity/meson.build
index d8e56b49c2..533efef2cb 100644
--- a/src/backend/utils/activity/meson.build
+++ b/src/backend/utils/activity/meson.build
@@ -18,6 +18,7 @@ backend_sources += files(
   'pgstat_subscription.c',
   'pgstat_wal.c',
   'pgstat_xact.c',
+  'pgstat_xlog.c',
 )
 
 # this includes a .c file with contents generated in ../../../include/activity,
diff --git a/src/backend/utils/activity/pgstat_xlog.c b/src/backend/utils/activity/pgstat_xlog.c
new file mode 100644
index 0000000000..59a06cd9e1
--- /dev/null
+++ b/src/backend/utils/activity/pgstat_xlog.c
@@ -0,0 +1,72 @@
+/* ----------
+ * pgstat_xlog.c
+ *	   WAL replay logic for cumulative statistics.
+ *
+ *
+ * Copyright (c) 2001-2025, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/activity/pgstat_xlog.c
+ * ----------
+ */
+
+#include "postgres.h"
+
+#include <unistd.h>
+
+#include "access/xlog.h"
+#include "access/xloginsert.h"
+#include "utils/pgstat_internal.h"
+#include "utils/pgstat_xlog.h"
+
+/*
+ * Write pgstats record data into WAL.
+ */
+XLogRecPtr
+pgstat_xlog_data(PgStat_Kind stats_kind, const void *data,
+				 size_t data_size)
+{
+	xl_pgstat_data xlrec;
+	XLogRecPtr	lsn;
+
+	xlrec.stats_kind = stats_kind;
+	xlrec.data_size = data_size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfPgStatData);
+	XLogRegisterData(data, data_size);
+
+	lsn = XLogInsert(RM_PGSTAT_ID, XLOG_PGSTAT_DATA);
+	return lsn;
+}
+
+/*
+ * Redo just passes down to the stats kind expected by this record
+ * data included in it.
+ */
+void
+pgstat_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+	xl_pgstat_data *xlrec;
+	PgStat_Kind stats_kind;
+	const PgStat_KindInfo *kind_info;
+
+	if (info != XLOG_PGSTAT_DATA)
+		elog(PANIC, "pgstat_redo: unknown op code %u", info);
+
+	xlrec = (xl_pgstat_data *) XLogRecGetData(record);
+
+	stats_kind = xlrec->stats_kind;
+	kind_info = pgstat_get_kind_info(stats_kind);
+
+	if (kind_info == NULL)
+		elog(FATAL, "pgstat_redo: invalid stats kind found: kind=%u",
+			 stats_kind);
+
+	if (kind_info->redo_cb == NULL)
+		elog(FATAL, "pgstat_redo: no redo callback found: kind=%s",
+			 kind_info->name);
+
+	kind_info->redo_cb(xlrec->data, xlrec->data_size);
+}
diff --git a/src/bin/pg_waldump/.gitignore b/src/bin/pg_waldump/.gitignore
index ec51f41c76..e5089b322d 100644
--- a/src/bin/pg_waldump/.gitignore
+++ b/src/bin/pg_waldump/.gitignore
@@ -13,6 +13,7 @@
 /logicalmsgdesc.c
 /mxactdesc.c
 /nbtdesc.c
+/pgstatdesc.c
 /relmapdesc.c
 /replorigindesc.c
 /rmgrdesc_utils.c
diff --git a/src/bin/pg_waldump/rmgrdesc.c b/src/bin/pg_waldump/rmgrdesc.c
index 6b8c17bb4c..05b4f2acd1 100644
--- a/src/bin/pg_waldump/rmgrdesc.c
+++ b/src/bin/pg_waldump/rmgrdesc.c
@@ -30,6 +30,7 @@
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
+#include "utils/pgstat_xlog.h"
 #include "utils/relmapper.h"
 
 #define PG_RMGR(symname,name,redo,desc,identify,startup,cleanup,mask,decode) \
diff --git a/src/bin/pg_waldump/t/001_basic.pl b/src/bin/pg_waldump/t/001_basic.pl
index 8d574a410c..70256ecccb 100644
--- a/src/bin/pg_waldump/t/001_basic.pl
+++ b/src/bin/pg_waldump/t/001_basic.pl
@@ -73,7 +73,8 @@ BRIN
 CommitTs
 ReplicationOrigin
 Generic
-LogicalMessage$/,
+LogicalMessage
+PgStat$/,
 	'rmgr list');
 
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index eb93debe10..4db1e7cf4b 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -4135,6 +4135,7 @@ xl_multixact_create
 xl_multixact_truncate
 xl_overwrite_contrecord
 xl_parameter_change
+xl_pgstat_data
 xl_relmap_update
 xl_replorigin_drop
 xl_replorigin_set
-- 
2.47.1

From 397540085a0f176806aa36d0c8c85f8a6dbbf938 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 10 Jan 2025 13:36:28 +0900
Subject: [PATCH v3 4/4] injection_points: Add option and tests for WAL-logging

This serves as a template for WAL-logging related to pgstats, based on
the variable-numbered stats the module includes.  Some TAP tests are
added to check the backend facility.
---
 .../injection_points/injection_points.c       | 19 ++++++-
 .../injection_points/injection_stats.c        | 54 +++++++++++++++++++
 .../injection_points/injection_stats.h        |  3 +-
 .../modules/injection_points/t/001_stats.pl   | 22 ++++++++
 src/tools/pgindent/typedefs.list              |  1 +
 5 files changed, 97 insertions(+), 2 deletions(-)

diff --git a/src/test/modules/injection_points/injection_points.c b/src/test/modules/injection_points/injection_points.c
index ad528d7775..c7f0d6d242 100644
--- a/src/test/modules/injection_points/injection_points.c
+++ b/src/test/modules/injection_points/injection_points.c
@@ -104,7 +104,7 @@ extern PGDLLEXPORT void injection_wait(const char *name,
 static bool injection_point_local = false;
 
 /*
- * GUC variable
+ * GUC variables
  *
  * This GUC is useful to control if statistics should be enabled or not
  * during a test with injection points, like for example if a test relies
@@ -112,6 +112,12 @@ static bool injection_point_local = false;
  */
 bool		inj_stats_enabled = false;
 
+/*
+ * This GUC controls if statistics of injection points should be logged
+ * into WAL or not.
+ */
+bool		inj_stats_wal_enabled = false;
+
 /* Shared memory init callbacks */
 static shmem_request_hook_type prev_shmem_request_hook = NULL;
 static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
@@ -534,6 +540,17 @@ _PG_init(void)
 							 NULL,
 							 NULL);
 
+	DefineCustomBoolVariable("injection_points.log_stats",
+							 "Enables WAL-logging for injection points statistics.",
+							 NULL,
+							 &inj_stats_wal_enabled,
+							 false,
+							 PGC_POSTMASTER,
+							 0,
+							 NULL,
+							 NULL,
+							 NULL);
+
 	MarkGUCPrefixReserved("injection_points");
 
 	/* Shared memory initialization */
diff --git a/src/test/modules/injection_points/injection_stats.c b/src/test/modules/injection_points/injection_stats.c
index 5db62bca66..df52cb026e 100644
--- a/src/test/modules/injection_points/injection_stats.c
+++ b/src/test/modules/injection_points/injection_stats.c
@@ -21,6 +21,7 @@
 #include "pgstat.h"
 #include "utils/builtins.h"
 #include "utils/pgstat_internal.h"
+#include "utils/pgstat_xlog.h"
 
 /* Structures for statistics of injection points */
 typedef struct PgStat_StatInjEntry
@@ -34,6 +35,14 @@ typedef struct PgStatShared_InjectionPoint
 	PgStat_StatInjEntry stats;
 } PgStatShared_InjectionPoint;
 
+/* Structure for data of injection points logged in WAL */
+typedef struct PgStat_StatInjRecord
+{
+	uint64		objid;			/* hash of the point name */
+	PgStat_StatInjEntry entry;	/* stats data */
+} PgStat_StatInjRecord;
+
+static void injection_stats_redo_cb(void *data, size_t data_size);
 static bool injection_stats_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
 
 static const PgStat_KindInfo injection_stats = {
@@ -48,6 +57,7 @@ static const PgStat_KindInfo injection_stats = {
 	.shared_data_off = offsetof(PgStatShared_InjectionPoint, stats),
 	.shared_data_len = sizeof(((PgStatShared_InjectionPoint *) 0)->stats),
 	.pending_size = sizeof(PgStat_StatInjEntry),
+	.redo_cb = injection_stats_redo_cb,
 	.flush_pending_cb = injection_stats_flush_cb,
 };
 
@@ -64,6 +74,31 @@ static const PgStat_KindInfo injection_stats = {
 /* Track if stats are loaded */
 static bool inj_stats_loaded = false;
 
+/*
+ * REDO callback for injection point stats.
+ */
+static void
+injection_stats_redo_cb(void *data, size_t data_size)
+{
+	PgStat_StatInjRecord *record_data = (PgStat_StatInjRecord *) data;
+	PgStat_StatInjEntry record_entry = record_data->entry;
+	PgStat_StatInjEntry *stat_entry;
+	PgStatShared_InjectionPoint *shstatent;
+	PgStat_EntryRef *entry_ref;
+
+	Assert(data_size == sizeof(PgStat_StatInjRecord));
+
+	/* create or fetch existing entry */
+	entry_ref = pgstat_prep_pending_entry(PGSTAT_KIND_INJECTION, InvalidOid,
+										  record_data->objid, NULL);
+
+	shstatent = (PgStatShared_InjectionPoint *) entry_ref->shared_stats;
+	stat_entry = &shstatent->stats;
+
+	/* Update the injection point statistics, overwriting any existing data */
+	*stat_entry = record_entry;
+}
+
 /*
  * Callback for stats handling
  */
@@ -72,6 +107,9 @@ injection_stats_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 {
 	PgStat_StatInjEntry *localent;
 	PgStatShared_InjectionPoint *shfuncent;
+	PgStat_StatInjRecord record_data;
+
+	memset(&record_data, 0, sizeof(PgStat_StatInjRecord));
 
 	localent = (PgStat_StatInjEntry *) entry_ref->pending;
 	shfuncent = (PgStatShared_InjectionPoint *) entry_ref->shared_stats;
@@ -81,8 +119,24 @@ injection_stats_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 
 	shfuncent->stats.numcalls += localent->numcalls;
 
+	record_data.objid = entry_ref->shared_entry->key.objid;
+	record_data.entry = shfuncent->stats;
+
 	pgstat_unlock_entry(entry_ref);
 
+	/*
+	 * Store the data in WAL, if not in recovery and if the option is enabled.
+	 */
+	if (!RecoveryInProgress() && inj_stats_wal_enabled)
+	{
+		XLogRecPtr	lsn;
+
+		lsn = pgstat_xlog_data(PGSTAT_KIND_INJECTION, &record_data,
+							   sizeof(PgStat_StatInjRecord));
+
+		/* Force a flush, to ensure persistency */
+		XLogFlush(lsn);
+	}
 	return true;
 }
 
diff --git a/src/test/modules/injection_points/injection_stats.h b/src/test/modules/injection_points/injection_stats.h
index ba310c52c7..baa8bb506c 100644
--- a/src/test/modules/injection_points/injection_stats.h
+++ b/src/test/modules/injection_points/injection_stats.h
@@ -15,8 +15,9 @@
 #ifndef INJECTION_STATS
 #define INJECTION_STATS
 
-/* GUC variable */
+/* GUC variables */
 extern bool inj_stats_enabled;
+extern bool inj_stats_wal_enabled;
 
 /* injection_stats.c */
 extern void pgstat_register_inj(void);
diff --git a/src/test/modules/injection_points/t/001_stats.pl b/src/test/modules/injection_points/t/001_stats.pl
index d4539fe872..4b34dd0a5a 100644
--- a/src/test/modules/injection_points/t/001_stats.pl
+++ b/src/test/modules/injection_points/t/001_stats.pl
@@ -75,4 +75,26 @@ $node->stop;
 $node->adjust_conf('postgresql.conf', 'shared_preload_libraries', "''");
 $node->start;
 
+# Stop the server and enable WAL, the stats are preserved after recovery.
+$node->stop;
+$node->append_conf(
+	'postgresql.conf', qq(
+shared_preload_libraries = 'injection_points'
+injection_points.log_stats = true
+));
+$node->start;
+
+# Two calls, both WAL-logged.
+$node->safe_psql('postgres',
+	"SELECT injection_points_attach('stats-wal-notice', 'notice');");
+$node->safe_psql('postgres',
+	"SELECT injection_points_run('stats-wal-notice');");
+$node->safe_psql('postgres',
+	"SELECT injection_points_run('stats-wal-notice');");
+$node->stop('immediate');
+$node->start;
+$numcalls = $node->safe_psql('postgres',
+	"SELECT injection_points_stats_numcalls('stats-wal-notice');");
+is($numcalls, '2', 'number of stats after crash with WAL-logging enabled');
+
 done_testing();
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 4db1e7cf4b..303a06b3fb 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2167,6 +2167,7 @@ PgStat_StatDBEntry
 PgStat_StatFuncEntry
 PgStat_StatInjEntry
 PgStat_StatInjFixedEntry
+PgStat_StatInjRecord
 PgStat_StatReplSlotEntry
 PgStat_StatSubEntry
 PgStat_StatTabEntry
-- 
2.47.1