Andres Freund wrote:
> I have to say, it makes me really uncomfortable to take such
> shortcuts. In other branches we are doing liveliness checks with
> MultiXactIdIsRunning() et al. Why isn't that necessary here? And how
> likely is that this won't cause breakage somewhere down the line because
> somebody doesn't know of that subtlety?
I came up with the attached last night, which should do the right thing
in both cases.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
*** a/src/backend/access/transam/multixact.c
--- b/src/backend/access/transam/multixact.c
***************
*** 1275,1280 **** retry:
--- 1275,1313 ----
}
/*
+ * MultiXactHasRunningRemoteMembers
+ * Does the given multixact have still-live members from
+ * transactions other than our own?
+ */
+ bool
+ MultiXactHasRunningRemoteMembers(MultiXactId multi)
+ {
+ MultiXactMember *members;
+ int nmembers;
+ int i;
+
+ nmembers = GetMultiXactIdMembers(multi, &members, true);
+ if (nmembers <= 0)
+ return false;
+
+ for (i = 0; i < nmembers; i++)
+ {
+ /* not interested in our own members */
+ if (TransactionIdIsCurrentTransactionId(members[i].xid))
+ continue;
+
+ if (TransactionIdIsInProgress(members[i].xid))
+ {
+ pfree(members);
+ return true;
+ }
+ }
+
+ pfree(members);
+ return false;
+ }
+
+ /*
* mxactMemberComparator
* qsort comparison function for MultiXactMember
*
*** a/src/backend/utils/time/tqual.c
--- b/src/backend/utils/time/tqual.c
***************
*** 686,693 **** HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, CommandId curcid,
if (tuple->t_infomask & HEAP_XMAX_INVALID) /* xid invalid */
return HeapTupleMayBeUpdated;
! if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask)) /* not deleter */
! return HeapTupleMayBeUpdated;
if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
{
--- 686,721 ----
if (tuple->t_infomask & HEAP_XMAX_INVALID) /* xid invalid */
return HeapTupleMayBeUpdated;
! if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
! {
! TransactionId xmax;
!
! xmax = HeapTupleHeaderGetRawXmax(tuple);
!
! /*
! * Careful here: even though this tuple was created by our own
! * transaction, it might be locked by other transactions, if
! * the original version was key-share locked when we updated
! * it.
! */
!
! if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
! {
! if (MultiXactHasRunningRemoteMembers(xmax))
! return HeapTupleBeingUpdated;
! else
! return HeapTupleMayBeUpdated;
! }
!
! /* if locker is gone, all's well */
! if (!TransactionIdIsInProgress(xmax))
! return HeapTupleMayBeUpdated;
!
! if (!TransactionIdIsCurrentTransactionId(xmax))
! return HeapTupleBeingUpdated;
! else
! return HeapTupleMayBeUpdated;
! }
if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
{
***************
*** 700,706 **** HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, CommandId curcid,
--- 728,738 ----
/* updating subtransaction must have aborted */
if (!TransactionIdIsCurrentTransactionId(xmax))
+ {
+ if (MultiXactHasRunningRemoteMembers(xmax))
+ return HeapTupleBeingUpdated;
return HeapTupleMayBeUpdated;
+ }
else
{
if (HeapTupleHeaderGetCmax(tuple) >= curcid)
*** a/src/include/access/multixact.h
--- b/src/include/access/multixact.h
***************
*** 89,94 **** extern bool MultiXactIdIsRunning(MultiXactId multi);
--- 89,95 ----
extern void MultiXactIdSetOldestMember(void);
extern int GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **xids,
bool allow_old);
+ extern bool MultiXactHasRunningRemoteMembers(MultiXactId multi);
extern bool MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2);
extern bool MultiXactIdPrecedesOrEquals(MultiXactId multi1,
MultiXactId multi2);
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