v14-0001-Rework-GetMultiXactInfo.patch

From dbe13b3d61c03f5d8d6773021e87c626ab04b3b0 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 29 Dec 2025 11:39:56 +0900
Subject: [PATCH v14 1/3] Rework GetMultiXactInfo()

This routine returned a number of offsets as a MultiXactOffset, but it
is not actually an offset, just a number to define their range.  This
was confusing.

This type confusion comes from the original implementation of
MultiXactMemberFreezeThreshold().
---
 src/include/access/multixact.h         |  2 +-
 src/backend/access/transam/multixact.c | 16 ++++++++--------
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/include/access/multixact.h b/src/include/access/multixact.h
index 6433fe163641..d22abbb72512 100644
--- a/src/include/access/multixact.h
+++ b/src/include/access/multixact.h
@@ -109,7 +109,7 @@ extern bool MultiXactIdIsRunning(MultiXactId multi, bool isLockOnly);
 extern void MultiXactIdSetOldestMember(void);
 extern int	GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members,
 								  bool from_pgupgrade, bool isLockOnly);
-extern void GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *members,
+extern void GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *nextOffset,
 							 MultiXactId *oldestMultiXactId,
 							 MultiXactOffset *oldestOffset);
 extern bool MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2);
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index 34956a5a6634..0d6f594e2a06 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -2461,25 +2461,23 @@ find_multixact_start(MultiXactId multi, MultiXactOffset *result)
  *
  * Returns information about the current MultiXact state, as of:
  * multixacts: Number of MultiXacts (nextMultiXactId - oldestMultiXactId)
- * members: Number of member entries (nextOffset - oldestOffset)
+ * nextOffset: Next-to-be-assigned offset
  * oldestMultiXactId: Oldest MultiXact ID still in use
  * oldestOffset: Oldest offset still in use
  */
 void
-GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *members,
+GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *nextOffset,
 				 MultiXactId *oldestMultiXactId, MultiXactOffset *oldestOffset)
 {
-	MultiXactOffset nextOffset;
 	MultiXactId nextMultiXactId;
 
 	LWLockAcquire(MultiXactGenLock, LW_SHARED);
-	nextOffset = MultiXactState->nextOffset;
+	*nextOffset = MultiXactState->nextOffset;
 	*oldestMultiXactId = MultiXactState->oldestMultiXactId;
 	nextMultiXactId = MultiXactState->nextMXact;
 	*oldestOffset = MultiXactState->oldestOffset;
 	LWLockRelease(MultiXactGenLock);
 
-	*members = nextOffset - *oldestOffset;
 	*multixacts = nextMultiXactId - *oldestMultiXactId;
 }
 
@@ -2514,16 +2512,18 @@ GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *members,
 int
 MultiXactMemberFreezeThreshold(void)
 {
-	MultiXactOffset members;
 	uint32		multixacts;
 	uint32		victim_multixacts;
 	double		fraction;
 	int			result;
 	MultiXactId oldestMultiXactId;
 	MultiXactOffset oldestOffset;
+	MultiXactOffset nextOffset;
+	uint64		members;
 
-	/* Read the current offsets and members usage. */
-	GetMultiXactInfo(&multixacts, &members, &oldestMultiXactId, &oldestOffset);
+	/* Read the current offsets and multixact usage. */
+	GetMultiXactInfo(&multixacts, &nextOffset, &oldestMultiXactId, &oldestOffset);
+	members = nextOffset - oldestOffset;
 
 	/* If member space utilization is low, no special action is required. */
 	if (members <= MULTIXACT_MEMBER_LOW_THRESHOLD)
-- 
2.51.0