v20260316-0001-Add-proper-WAL-record-for-XLOG_CHECKPOINT_.patch

From 5a3e1f613dc8ae6977282c4f6028c33c01540984 Mon Sep 17 00:00:00 2001
From: Daniel Gustafsson <dgustafsson@postgresql.org>
Date: Thu, 12 Mar 2026 18:33:02 +0100
Subject: [PATCH v20260316 1/2] Add proper WAL record for XLOG_CHECKPOINT_REDO

XLOG_CHECKPOINT_REDO only contains the wal_level copied straight in
without an encapsulating record structure. While it works, it makes
future uses of XLOG_CHECKPOINT_REDO hard as there is nowhere to put
new data items.  This fix this was inspired by the online checksums
patch which adds data to this record, but this change has value on
its own.

Author: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/..
---
 src/backend/access/rmgrdesc/xlogdesc.c | 6 +++---
 src/backend/access/transam/xlog.c      | 8 +++++++-
 src/backend/postmaster/walsummarizer.c | 5 ++++-
 src/include/access/xlog_internal.h     | 6 ++++++
 src/tools/pgindent/typedefs.list       | 1 +
 5 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/src/backend/access/rmgrdesc/xlogdesc.c b/src/backend/access/rmgrdesc/xlogdesc.c
index 9044b952117..44194d3ea17 100644
--- a/src/backend/access/rmgrdesc/xlogdesc.c
+++ b/src/backend/access/rmgrdesc/xlogdesc.c
@@ -163,10 +163,10 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
 	}
 	else if (info == XLOG_CHECKPOINT_REDO)
 	{
-		int			wal_level;
+		xl_checkpoint_redo xlrec;
 
-		memcpy(&wal_level, rec, sizeof(int));
-		appendStringInfo(buf, "wal_level %s", get_wal_level_string(wal_level));
+		memcpy(&xlrec, rec, sizeof(xl_checkpoint_redo));
+		appendStringInfo(buf, "wal_level %s", get_wal_level_string(xlrec.wal_level));
 	}
 	else if (info == XLOG_LOGICAL_DECODING_STATUS_CHANGE)
 	{
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..2c1c6f88b74 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7179,9 +7179,15 @@ CreateCheckPoint(int flags)
 	 */
 	if (!shutdown)
 	{
+		xl_checkpoint_redo redo_rec;
+
+		WALInsertLockAcquire();
+		redo_rec.wal_level = wal_level;
+		WALInsertLockRelease();
+
 		/* Include WAL level in record for WAL summarizer's benefit. */
 		XLogBeginInsert();
-		XLogRegisterData(&wal_level, sizeof(wal_level));
+		XLogRegisterData(&redo_rec, sizeof(xl_checkpoint_redo));
 		(void) XLogInsert(RM_XLOG_ID, XLOG_CHECKPOINT_REDO);
 
 		/*
diff --git a/src/backend/postmaster/walsummarizer.c b/src/backend/postmaster/walsummarizer.c
index e1aa102f41d..bdc2236a8c1 100644
--- a/src/backend/postmaster/walsummarizer.c
+++ b/src/backend/postmaster/walsummarizer.c
@@ -1428,8 +1428,11 @@ SummarizeXlogRecord(XLogReaderState *xlogreader, bool *new_fast_forward)
 
 	if (info == XLOG_CHECKPOINT_REDO)
 	{
+		xl_checkpoint_redo xlrec;
+
 		/* Payload is wal_level at the time record was written. */
-		memcpy(&record_wal_level, XLogRecGetData(xlogreader), sizeof(int));
+		memcpy(&xlrec, XLogRecGetData(xlogreader), sizeof(xl_checkpoint_redo));
+		record_wal_level = xlrec.wal_level;
 	}
 	else if (info == XLOG_CHECKPOINT_SHUTDOWN)
 	{
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..faabba73ef2 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -303,6 +303,12 @@ typedef struct xl_end_of_recovery
 	int			wal_level;
 } xl_end_of_recovery;
 
+/* checkpoint redo */
+typedef struct xl_checkpoint_redo
+{
+	int			wal_level;
+} xl_checkpoint_redo;
+
 /*
  * The functions in xloginsert.c construct a chain of XLogRecData structs
  * to represent the final WAL record.
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 52f8603a7be..3e6a0aae828 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -4379,6 +4379,7 @@ xl_btree_split
 xl_btree_unlink_page
 xl_btree_update
 xl_btree_vacuum
+xl_checkpoint_redo
 xl_clog_truncate
 xl_commit_ts_truncate
 xl_dbase_create_file_copy_rec
-- 
2.39.3 (Apple Git-146)