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Re: VM corruption on standby

Kirill Reshke <reshkekirill@gmail.com>

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From: Kirill Reshke <reshkekirill@gmail.com>
To: Aleksander Alekseev <aleksander@tigerdata.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Andrey Borodin <x4mmm@yandex-team.ru>, Melanie Plageman <melanieplageman@gmail.com>
Date: 2025-08-10T05:45:15Z
Lists: pgsql-hackers 
On Sun, 10 Aug 2025 at 01:55, Aleksander Alekseev
<aleksander@tigerdata.com> wrote:
> For this reason we have PageHeaderData.pd_lsn for instance - to make sure
> pages are evicted only *after* the record that changed it is written
> to disk (because WAL records can't be applied to pages from the
> future).

We don't bump the LSN of the heap page when setting the visibility
map bit.

> I guess the intent here could be to do an optimization of some sort
> but the facts that 1. the instance can be killed at any time and 2.
> there might be replicas - were not considered.

> IMHO: logging the changes first, then allowing to evict the page.

Clearing the vm before the logging changes was intentional [0].
So I assume we should not change the approach, but rather just tweak
things a bit to make the whole thing work.

[0] https://www.postgresql.org/message-id/BANLkTimuLk4RHXSQHEEiYGbxiXp2mh5KCA%40mail.gmail.com

-- 
Best regards,
Kirill Reshke

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Revert "Get rid of WALBufMappingLock"

  2. Get rid of WALBufMappingLock

  3. Split WaitEventSet functions to separate source file

  4. Add WL_EXIT_ON_PM_DEATH pseudo-event.