Re: [COMMITTERS] pgsql: Fix traversal of half-frozen update chains

On Tue, Oct 17, 2017 at 12:23 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> On Tue, Oct 17, 2017 at 3:40 AM, Alvaro Herrera <alvherre@alvh.no-ip.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.

BTW, seems worth fixing this old comment above
heap_prepare_freeze_tuple() while you're at it:
* NB: It is not enough to set hint bits to indicate something is* committed/invalid -- they might not be set on a
standby,or after crash* recovery.  We really need to remove old xids.
 



-- 
Peter Geoghegan


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