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Commit 5174206

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alvherrealvherre
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Fix thinko in lock mode enum
Commit 0e5680f contained a thinko mixing LOCKMODE with LockTupleMode. This caused misbehavior in the case where a tuple is marked with a multixact with at most a FOR SHARE lock, and another transaction tries to acquire a FOR NO KEY EXCLUSIVE lock; this case should block but doesn't. Include a new isolation tester spec file to explicitely try all the tuple lock combinations; without the fix it shows the problem: starting permutation: s1_begin s1_lcksvpt s1_tuplock2 s2_tuplock3 s1_commit step s1_begin: BEGIN; step s1_lcksvpt: SELECT * FROM multixact_conflict FOR KEY SHARE; SAVEPOINT foo; a 1 step s1_tuplock2: SELECT * FROM multixact_conflict FOR SHARE; a 1 step s2_tuplock3: SELECT * FROM multixact_conflict FOR NO KEY UPDATE; a 1 step s1_commit: COMMIT; With the fixed code, step s2_tuplock3 blocks until session 1 commits, which is the correct behavior. All other cases behave correctly. Backpatch to 9.3, like the commit that introduced the problem.
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‎src/backend/access/heap/heapam.c

Lines changed: 4 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -6111,6 +6111,7 @@ DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
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int nmembers;
61126112
MultiXactMember *members;
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bool result = false;
6114+
LOCKMODE wanted = tupleLockExtraInfo[lockmode].hwlock;
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allow_old = !(infomask & HEAP_LOCK_MASK) && HEAP_XMAX_IS_LOCKED_ONLY(infomask);
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nmembers = GetMultiXactIdMembers(multi, &members, allow_old);
@@ -6121,11 +6122,12 @@ DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
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for (i = 0; i < nmembers; i++)
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{
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TransactionId memxid;
6124-
LockTupleMode memlockmode;
6125+
LOCKMODE memlockmode;
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memlockmode = LOCKMODE_from_mxstatus(members[i].status);
6128+
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/* ignore members that don't conflict with the lock we want */
6128-
if (!DoLockModesConflict(memlockmode, lockmode))
6130+
if (!DoLockModesConflict(memlockmode, wanted))
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continue;
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/* ignore members from current xact */

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