Horton

Re: BUG #17485: Records missing from Primary Key index when doing REINDEX INDEX CONCURRENTLY

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Peter Geoghegan <pg@bowt.ie>, Michael Paquier <michael@paquier.xyz>, Andrey Borodin <x4mmm@yandex-team.ru>, Петър Славов <pet.slavov@gmail.com>, PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Date: 2022-05-24T18:37:05Z
Lists: pgsql-bugs 
Hi,

On 2022-05-24 11:15:42 -0700, Andres Freund wrote:
> I suspect the problem might be related to pruning done during the validation
> scan. Once PROC_IN_SAFE_IC is set, the backend itself will not preserve tids
> its own snapshot might need. Which will wreak havoc during the validation
> scan.

Looking at it more, I don't see when PROC_IN_SAFE_IC is safe as defined,
tbh. Afaict it basically completely breaks snapshots - which we rely on to
work for both the initial build scan and then for the validation scan.

It seems safe to make CIC to ignore other CICs when deciding whether to wait
for those transactions. But it seems utterly unsafe to ignore CICs when when
determining horizons.

Greetings,

Andres Freund

Commits

  1. Revert changes to CONCURRENTLY that "sped up" Xmin advance

  2. Fix possible HOT corruption when RECENTLY_DEAD changes to DEAD while pruning.