| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Peter Geoghegan <pg(at)bowt(dot)ie>, Chris Travers <chris(at)orioledata(dot)com>, Aleksander Alekseev <aleksander(at)timescale(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Chris Travers <chris(dot)travers(at)gmail(dot)com>, Fedor Sigaev <teodor(at)sigaev(dot)ru>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Konstantin Knizhnik <knizhnik(at)garret(dot)ru>, Nikita Glukhov <n(dot)gluhov(at)postgrespro(dot)ru>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, Maxim Orlov <orlovmg(at)gmail(dot)com>, Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com>, Simon Riggs <simon(dot)riggs(at)enterprisedb(dot)com> |
| Subject: | Re: Add 64-bit XIDs into PostgreSQL 15 |
| Date: | 2022-11-28 21:52:27 |
| Message-ID: | Y4Utm0IPmkoYrZ7m@momjian.us |
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| Lists: | pgsql-hackers |
On Mon, Nov 28, 2022 at 04:30:22PM -0500, Robert Haas wrote:
> What is the purpose of using 64-bit XIDs, if not to avoid having to
> stop the world when we run short of XIDs?
>
> I'd say that if this patch, or any patch with broadly similar goals,
> fails to remove xidStopLimit, it might as well not exist.
>
> xidStopLimit is not a general defense against falling too far behind
> on freezing, and in general, there is no reason to think that we need
> such a defense. xidStopLimit is a defense against reusing the same XID
> and thus causing irreversible database corruption. When that
> possibility no longer exists, it has outlived its usefulness and we
> should be absolutely delighted to bid it adieu.
>
> It seems like you and Chris are proposing the moral equivalent of
> paying off your home loan but still sending a check to the mortgage
> company every month just to be sure they don't get mad.
I think the problem is that we still have bloat with 64-bit XIDs,
specifically pg_xact and pg_multixact files. Yes, that bloat is less
serious, but it is still an issue worth reporting in the server logs,
though not serious enough to stop the server from write queries.
--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com
Embrace your flaws. They make you human, rather than perfect,
which you will never be.
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