v1-0002-Fix-the-mxid-and-mxoff-wraparound-issues-in-pg_up.patch

From dd5775184a729c2b5cfff40ff5ab55eed936d2fb Mon Sep 17 00:00:00 2001
From: Maxim Orlov <orlovmg@gmail.com>
Date: Fri, 20 Jun 2025 17:21:08 +0300
Subject: [PATCH v1 2/2] Fix the mxid and mxoff wraparound issues in
 pg_upgrade.

Per bags:
- BUG #18863: Multixact wraparound and pg_resetwal error "multitransaction ID (-m) must not be 0"
- BUG #18865: pg_resetwal error: multitransaction offset (-O) must not be -1
---
 src/bin/pg_resetwal/pg_resetwal.c |  5 +----
 src/bin/pg_upgrade/pg_upgrade.c   | 11 ++++++++++-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/bin/pg_resetwal/pg_resetwal.c b/src/bin/pg_resetwal/pg_resetwal.c
index e876f35f38..3b984eeae0 100644
--- a/src/bin/pg_resetwal/pg_resetwal.c
+++ b/src/bin/pg_resetwal/pg_resetwal.c
@@ -273,8 +273,6 @@ main(int argc, char *argv[])
 					pg_log_error_hint("Try \"%s --help\" for more information.", progname);
 					exit(1);
 				}
-				if (set_mxoff == -1)
-					pg_fatal("multitransaction offset (-O) must not be -1");
 				break;
 
 			case 'l':
@@ -463,8 +461,7 @@ main(int argc, char *argv[])
 		ControlFile.checkPointCopy.oldestMultiDB = InvalidOid;
 	}
 
-	if (set_mxoff != -1)
-		ControlFile.checkPointCopy.nextMultiOffset = set_mxoff;
+	ControlFile.checkPointCopy.nextMultiOffset = set_mxoff;
 
 	if (minXlogTli > ControlFile.checkPointCopy.ThisTimeLineID)
 	{
diff --git a/src/bin/pg_upgrade/pg_upgrade.c b/src/bin/pg_upgrade/pg_upgrade.c
index 536e49d261..0bfca6865e 100644
--- a/src/bin/pg_upgrade/pg_upgrade.c
+++ b/src/bin/pg_upgrade/pg_upgrade.c
@@ -793,6 +793,15 @@ copy_xact_xlog_xid(void)
 	if (old_cluster.controldata.cat_ver >= MULTIXACT_FORMATCHANGE_CAT_VER &&
 		new_cluster.controldata.cat_ver >= MULTIXACT_FORMATCHANGE_CAT_VER)
 	{
+		uint32	old_chkpnt_nxtmulti = old_cluster.controldata.chkpnt_nxtmulti;
+
+		/*
+		 * Beware of the possibility that chkpnt_nxtmulti is in the
+		 * wrapped-around state in old cluster.
+		 */
+		if (old_chkpnt_nxtmulti == 0)
+			old_chkpnt_nxtmulti = 1;	/* FirstMultiXactId */
+
 		copy_subdir_files("pg_multixact/offsets", "pg_multixact/offsets");
 		copy_subdir_files("pg_multixact/members", "pg_multixact/members");
 
@@ -806,7 +815,7 @@ copy_xact_xlog_xid(void)
 				  "\"%s/pg_resetwal\" -O %u -m %u,%u \"%s\"",
 				  new_cluster.bindir,
 				  old_cluster.controldata.chkpnt_nxtmxoff,
-				  old_cluster.controldata.chkpnt_nxtmulti,
+				  old_chkpnt_nxtmulti,
 				  old_cluster.controldata.chkpnt_oldstMulti,
 				  new_cluster.pgdata);
 		check_ok();
-- 
2.43.0