Re: On conflict update & hint bits

On Sat, Oct 1, 2016 at 5:15 AM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> On Fri, Sep 30, 2016 at 5:33 PM, Konstantin Knizhnik
> <k(dot)knizhnik(at)postgrespro(dot)ru> wrote:
>> So the question is whether it is correct that ExecOnConflictUpdate tries to
>> access and update tuple without holding lock on the buffer?
>
> You're right -- this is a bug in Postgres.

(Thomas Munro and Kevin Grittner added to CC list.)

Attached is a revision of Thomas' patch to fix a related issue; it now
also fixes this no-buffer-lock-held issue. He posted his version of
this to a -general mailing list thread a week ago [1]. This was a
thread about spurious serialization failure with ON CONFLICT DO
NOTHING. I understand that Kevin is still not happy with the behavior
under SSI even with our fix, since serialization failures will still
occur more often than necessary (see other thread for details of what
I'm talking about).

I believe this patch to be a strict improvement on master, and I
suggest it be applied in advance of the deadline to get fixes in for
the next set of point releases. Note that this revision includes
Thomas' isolation test, which is completely unchanged. I still intend
to work with Kevin to do better than this under SSI, though that will
probably be for a future point release. The behavior proposed by my
fix here is the right thing for REPEATABLE READ isolation level, which
has nothing to do with Kevin's proposed more careful handling under
SSI. Besides, the buffer pin bug reported by Konstantin on this thread
really should be addressed ASAP.

[1] https://www.postgresql.org/message-id/CAEepm=3Ra9NgDHocDBtB4iiB7MWdavQybNS3F47SvKh1Mk-mFQ@mail.gmail.com
--
Peter Geoghegan