Re: MultiXact bugs

Andres Freund <andres(at)2ndquadrant(dot)com> wrote:

> HeapTupleHeaderGetUpdateXid() ignores aborted updaters
> and returns InvalidTransactionId in that case, but
> HeapTupleSatisfiesVacuum() returns HEAPTUPLE_DELETE_IN_PROGRESS...

That sure *sounds* like it should cause a problem for this code in
CheckForSerializableConflictOut():

    htsvResult = HeapTupleSatisfiesVacuum(tuple, TransactionXmin, buffer);
    switch (htsvResult)
    {
        [ ... ]
        case HEAPTUPLE_DELETE_IN_PROGRESS:
            xid = HeapTupleHeaderGetUpdateXid(tuple->t_data);
            break;
        [ ... ]
    }
    Assert(TransactionIdIsValid(xid));

... however, I have not been able to trigger that Assert even with
gdb breakpoints at what I think are the right spots.  Any
suggestions?  How far back is it true that the above
HeapTupleSatisfiesVacuum() can return HEAPTUPLE_DELETE_IN_PROGRESS
but HeapTupleHeaderGetUpdateXid(tuple->t_data) on the exact same
tuple structure can return InvalidTransactionId?  Is there some
other condition (besides a ROLLBACK of an UPDATE on the tuple being
read) which needs to be met?  Is any particular timing necessary?

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company