Horton

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

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Amit Kapila <amit.kapila16@gmail.com>, 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>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Stephen Frost <sfrost@snowman.net>
Date: 2020-10-15T08:37:35Z
Lists: pgsql-hackers

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Hi,

On 2020-09-21 14:20:03 -0700, Andres Freund wrote:
> I can give it a try. I can see several paths of varying invasiveness,
> not sure yet what the best approach is. Let me think about if for a bit.

Ugh, sorry for taking so long to get around to this.

Attached is a *prototype* implemention of this concept, which clearly is
lacking some comment work (and is intentionally lacking some
re-indentation).

I described my thoughts about how to limit the horizons for temp tables in
https://www.postgresql.org/message-id/20201014203103.72oke6hqywcyhx7s%40alap3.anarazel.de

Besides comments this probably mainly needs a bit more tests around temp
table vacuuming. Should have at least an isolation test that verifies
that temp table rows can be a) vacuumed b) pruned away in the presence
of other sessions with xids.

Greetings,

Andres Freund

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.