Horton
Menu

Re: IPC/MultixactCreation on the Standby server

Kirill Reshke <reshkekirill@gmail.com>

View thread
From: Kirill Reshke <reshkekirill@gmail.com>
To: Andrey Borodin <x4mmm@yandex-team.ru>
Cc: Dmitry <dsy.075@yandex.ru>, Álvaro Herrera <alvherre@kurilemu.de>, pgsql-hackers@lists.postgresql.org
Date: 2025-08-20T08:19:47Z
Lists: pgsql-hackers 
On Thu, 31 Jul 2025 at 11:29, Andrey Borodin <x4mmm@yandex-team.ru> wrote:
>
>
>
> > On 29 Jul 2025, at 23:15, Andrey Borodin <x4mmm@yandex-team.ru> wrote:
> >
> > I do not understand it yet.
>
> OK, I figured it out. SimpleLruDoesPhysicalPageExist() was reading a physical file and could race with real extension by ExtendMultiXactOffset().
> So I used ExtendMultiXactOffset(actual + 1). I hope this does not open a loop for wraparound...
>
> Here's an updated two patches, one for Postgres 17 and one for mater(with a test).

Hi!

+ /*
+ * We might have filled this offset previosuly.
+ * Cross-check for correctness.
+ */
+ Assert((*offptr == 0) || (*offptr == offset));

Should we exit here with errcode(ERRCODE_DATA_CORRUPTED) if *offptr !=
0 and *offptr != offset?


+ /* Read and adjust next page */
+ next_slotno = SimpleLruReadPage(MultiXactOffsetCtl, next_pageno, true, next);
+ next_offptr = (MultiXactOffset *)
MultiXactOffsetCtl->shared->page_buffer[next_slotno];
+ next_offptr[next_entryno] = offset + nmembers;

should we check the value of next_offptr[next_entryno] to be equal to
zero or  offset + nmembers ? Assert or
errcode(ERRCODE_DATA_CORRUPTED) also.



-- 
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. Fix test to work with non-8kB block sizes

  2. Fix setting next multixid's offset at offset wraparound

  3. Add test for multixid wraparound

  4. Set next multixid's offset when creating a new multixid

  5. psql: Improve tab completion for large objects.

  6. Refactor some repetitive SLRU code

  7. Transaction IDs wrap around, per my proposal of 13-Aug-01. More