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Re: IPC/MultixactCreation on the Standby server

Andrey Borodin <x4mmm@yandex-team.ru>

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From: Andrey Borodin <x4mmm@yandex-team.ru>
To: Dmitry <dsy.075@yandex.ru>
Cc: Álvaro Herrera <alvherre@kurilemu.de>, pgsql-hackers@lists.postgresql.org
Date: 2025-07-29T18:15:28Z
Lists: pgsql-hackers 

> On 29 Jul 2025, at 12:17, Dmitry <dsy.075@yandex.ru> wrote:
> 
> But on the master, some of the requests then fail with an error, apparently invalid multixact's remain in the pages.

Thanks!

That's a bug in my patch. I do not understand it yet. I've reproduced it with your original workload.
Most of errors I see are shallow (offset == 0 or nextOffset==0), but this one is interesting:

TRAP: failed Assert("shared->page_number[slotno] == pageno && shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS"), File: "slru.c", Line: 729, PID: 91085
0   postgres                            0x00000001032ea5ac ExceptionalCondition + 216
1   postgres                            0x0000000102af2784 SlruInternalWritePage + 700
2   postgres                            0x0000000102af14dc SimpleLruWritePage + 96
3   postgres                            0x0000000102ae89d4 RecordNewMultiXact + 576

So it makes me think that it's some version of IO concurrency issue.
As expected error only persists if "extend SLRU" branch is active in RecordNewMultiXact().

Thanks for testing!


Best regards, Andrey Borodin.

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