Horton

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

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
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: 2020-09-21T21:03:53Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2020-09-21 16:40:40 -0400, Tom Lane wrote:
>> Andres Freund <andres@anarazel.de> writes:
>>> I think that's an argument for what I suggested elsewhere, which is that
>>> we should move the logic for a different horizon for temp tables out of
>>> vacuum_set_xid_limits, and into procarray.

>> But procarray does not seem like a great place for
>> table-persistence-dependent decisions either?

> That ship has sailed a long long time ago though. GetOldestXmin() has
> looked at the passed in relation for a quite a while, and even before
> that we had logic about 'allDbs' etc.  It doesn't easily seem possible
> to avoid that, given how intimately that's coupled with how snapshots
> are built and used, database & vacuumFlags checks etc.

OK.  Given that you've got strong feelings about this, do you want to
propose a patch?  I'm happy to fix it, since it's at least in part my
bug, but I probably won't do it exactly like you would.

			regards, tom lane

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.