Re: pgsql: Fix traversal of half-frozen update chains

On Tue, Oct 17, 2017 at 3:40 AM, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> Peter Geoghegan wrote:
>
>> Wouldn't this last "if" test, to cover the pg_upgrade case, be better
>> targeted by comparing *raw* xmin to FrozenTransactionId? You're using
>> the potentially distinct xmin value returned by
>> HeapTupleHeaderGetXmin() for the test here. I think we should be
>> directly targeting tuples frozen on or before 9.4 (prior to
>> pg_upgrade) instead.
>
> I also realized we can stop checking (i.e. don't compare xmin to
> frozenxid) if the XMIN_FROZEN bits are set -- because in that case the
> tuple cannot possibly come from 9.3 frozen. So I think this should do
> it.
>
> (New HeapTupleUpdateXmaxMatchesXmin() implementation)

Yeah, this is what I had in mind, too.

--
Peter Geoghegan