From 138b11e1a787f0d2b3fc913eec3c8d28527ee76c Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Thu, 11 Dec 2025 18:03:10 +0200
Subject: [PATCH v1 2/2] Fix the bug with priorXmax

---
 src/backend/access/heap/heapam.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index a69df8bd431..5fb81af8d4f 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -86,6 +86,7 @@ static void compute_new_xmax_infomask(TransactionId xmax, uint16 old_infomask,
 									  TransactionId *result_xmax, uint16 *result_infomask,
 									  uint16 *result_infomask2);
 static TM_Result heap_lock_updated_tuple(Relation rel, HeapTuple tuple,
+										 TransactionId priorXmax,
 										 const ItemPointerData *ctid, TransactionId xid,
 										 LockTupleMode mode);
 static void GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
@@ -4818,9 +4819,16 @@ l3:
 				 */
 				if (follow_updates && updated)
 				{
+					TransactionId updateXid;
 					TM_Result	res;
 
-					res = heap_lock_updated_tuple(relation, tuple, &t_ctid,
+					if (infomask & HEAP_XMAX_IS_MULTI)
+						updateXid = MultiXactIdGetUpdateXid(xwait, infomask);
+					else
+						updateXid = xwait;
+
+					res = heap_lock_updated_tuple(relation, tuple, updateXid,
+												  &t_ctid,
 												  GetCurrentTransactionId(),
 												  mode);
 					if (res != TM_Ok)
@@ -5065,9 +5073,16 @@ l3:
 			/* if there are updates, follow the update chain */
 			if (follow_updates && !HEAP_XMAX_IS_LOCKED_ONLY(infomask))
 			{
+				TransactionId updateXid;
 				TM_Result	res;
 
-				res = heap_lock_updated_tuple(relation, tuple, &t_ctid,
+				if (infomask & HEAP_XMAX_IS_MULTI)
+					updateXid = MultiXactIdGetUpdateXid(xwait, infomask);
+				else
+					updateXid = xwait;
+
+				res = heap_lock_updated_tuple(relation, tuple, updateXid,
+											  &t_ctid,
 											  GetCurrentTransactionId(),
 											  mode);
 				if (res != TM_Ok)
@@ -5721,7 +5736,8 @@ test_lockmode_for_conflict(MultiXactStatus status, TransactionId xid,
  * version as well.
  */
 static TM_Result
-heap_lock_updated_tuple_rec(Relation rel, const ItemPointerData *tid, TransactionId xid,
+heap_lock_updated_tuple_rec(Relation rel, TransactionId priorXmax,
+							const ItemPointerData *tid, TransactionId xid,
 							LockTupleMode mode)
 {
 	TM_Result	result;
@@ -5734,7 +5750,6 @@ heap_lock_updated_tuple_rec(Relation rel, const ItemPointerData *tid, Transactio
 				old_infomask2;
 	TransactionId xmax,
 				new_xmax;
-	TransactionId priorXmax = InvalidTransactionId;
 	bool		cleared_all_frozen = false;
 	bool		pinned_desired_page;
 	Buffer		vmbuffer = InvalidBuffer;
@@ -6066,7 +6081,8 @@ out_unlocked:
  * levels, because that would lead to a serializability failure.
  */
 static TM_Result
-heap_lock_updated_tuple(Relation rel, HeapTuple tuple, const ItemPointerData *ctid,
+heap_lock_updated_tuple(Relation rel, HeapTuple tuple, TransactionId priorXmax,
+						const ItemPointerData *ctid,
 						TransactionId xid, LockTupleMode mode)
 {
 	INJECTION_POINT("heap_lock_updated_tuple", NULL);
@@ -6089,7 +6105,7 @@ heap_lock_updated_tuple(Relation rel, HeapTuple tuple, const ItemPointerData *ct
 		 */
 		MultiXactIdSetOldestMember();
 
-		return heap_lock_updated_tuple_rec(rel, ctid, xid, mode);
+		return heap_lock_updated_tuple_rec(rel, priorXmax, ctid, xid, mode);
 	}
 
 	/* nothing to lock */
-- 
2.47.3