Horton

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

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Ashutosh Sharma <ashu.coek88@gmail.com>
Cc: "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>, Tom Lane <tgl@sss.pgh.pa.us>, Stephen Frost <sfrost@snowman.net>
Date: 2020-08-06T15:48:51Z
Lists: pgsql-hackers 
On Thu, Aug 6, 2020 at 2:11 AM Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
> Okay, If you want I can remove the restriction on a toast table, but,
> then that means a user can directly remove the data chunks from the
> toast table without changing anything in the main table. This means we
> won't be able to query the main table as it will fail with an error
> like "ERROR:  unexpected chunk number ...". So, we will have to find
> some way to identify the pointer to the chunks that got deleted from
> the toast table and remove that pointer from the main table. We also
> need to make sure that before we remove a tuple (pointer) from the
> main table, we identify all the remaining data chunks pointed by this
> tuple and remove them completely only then that table would be
> considered to be in a good state. Now, I am not sure if we can
> currently do all these things.

That's the user's problem. If they don't have a plan for that, they
shouldn't use this tool. I don't think we can or should try to handle
it in this code.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.