Horton

Re: Vacuum ERRORs out considering freezing dead tuples from before OldestXmin

Melanie Plageman <melanieplageman@gmail.com>

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From: Melanie Plageman <melanieplageman@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Peter Geoghegan <pg@bowt.ie>, Pg Hackers <pgsql-hackers@postgresql.org>, Noah Misch <noah@leadboat.com>
Date: 2024-06-25T15:39:03Z
Lists: pgsql-hackers

Commits

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  1. Test that vacuum removes tuples older than OldestXmin

  2. Lower minimum maintenance_work_mem to 64kB

  3. Add accidentally omitted test to meson build file

  4. Use DELETE instead of UPDATE to speed up vacuum test

  5. Revert "Test that vacuum removes tuples older than OldestXmin"

  6. Ensure vacuum removes all visibly dead tuples older than OldestXmin

On Tue, Jun 25, 2024 at 10:31 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Tue, Jun 25, 2024 at 9:07 AM Andres Freund <andres@anarazel.de> wrote:
> > It's not hard - but it has downsides. It'll mean that - outside of vacuum -
> > we'll much more often not react to horizons going backwards due to
> > hot_standby_feedback. Which means that hot_standby_feedback, when used without
> > slots, will prevent fewer conflicts.
>
> Can you explain this in more detail?

If we prevent GlobalVisState from moving backward, then we would less
frequently be pushing the horizon backward on the primary in response
to hot standby feedback. Then, the primary would do more things that
would not be safely replayable on the standby -- so the standby could
end up encountering more recovery conflicts.

- Melanie