Horton

Re: recovering from "found xmin ... from before relfrozenxid ..."

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, Ashutosh Sharma <ashu.coek88@gmail.com>, Mark Dilger <mark.dilger@enterprisedb.com>, Masahiko Sawada <masahiko.sawada@2ndquadrant.com>, "Andrey M. Borodin" <x4mmm@yandex-team.ru>, MBeena Emerson <mbeena.emerson@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Andres Freund <andres@anarazel.de>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Stephen Frost <sfrost@snowman.net>
Date: 2020-09-19T12:28:14Z
Lists: pgsql-hackers 
On Sat, Sep 19, 2020 at 4:03 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Robert Haas <robertmhaas@gmail.com> writes:
> > Cool, thanks to both of you for looking. Committed.
>
> Hmph, according to whelk this is worse not better:
>
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=whelk&dt=2020-09-18%2017%3A42%3A11
>
> I'm at a loss to understand what's going on there.
>

I think our assumption that changing the tests to have temp tables
will make them safe w.r.t concurrent activity doesn't seem to be
correct. We do set OldestXmin for temp tables aggressive enough that
it allows us to remove all dead tuples but the test case behavior lies
on whether we are able to prune the chain. AFAICS, we are using
different cut-offs in heap_page_prune when it is called via
lazy_scan_heap. So that seems to be causing both the failures.

-- 
With Regards,
Amit Kapila.

Commits

  1. Fix wrong data table horizon computation during backend startup.

  2. Centralize horizon determination for temp tables, fixing bug due to skew.

  3. pg_surgery: Try to stabilize regression tests.

  4. New contrib module, pg_surgery, with heap surgery functions.

  5. Set cutoff xmin more aggressively when vacuuming a temporary table.

  6. snapshot scalability: Don't compute global horizons while building snapshots.

  7. Introduce vacuum errcontext to display additional information.