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: 2020-08-03T13:35:49Z
Lists: pgsql-hackers 
On Mon, Aug 3, 2020 at 5:05 AM Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
> Could you please explain this point once more in detail? I am not quite able to understand under what circumstances a buffer would be modified, but won't be marked as dirty or a WAL won't be written for it.

Whenever this branch is taken:

+               if (nskippedItems == noffs)
+                       goto skip_wal;

At this point you have already modified the page, using ItemIdSetDead,
HeapTupleHeaderSet*, and/or directly adjusting htup->infomask. If this
branch is taken, then MarkBufferDirty() and log_newpage_buffer() are
skipped.

-- 
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.