| From: | "Matheus Alcantara" <matheusssilv97(at)gmail(dot)com> |
|---|---|
| To: | "Masahiko Sawada" <sawada(dot)mshk(at)gmail(dot)com> |
| Cc: | "Daniil Davydov" <3danissimo(at)gmail(dot)com>, Álvaro Herrera <alvherre(at)kurilemu(dot)de>, "Alexandra Wang" <alexandra(dot)wang(dot)oss(at)gmail(dot)com>, "PostgreSQL Hackers" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: LISTEN/NOTIFY bug: VACUUM sets frozenxid past a xid in async queue |
| Date: | 2025-08-21 23:14:47 |
| Message-ID: | DC8HKDZVIDYG.12H0X267CHMO5@gmail.com |
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| Lists: | pgsql-hackers |
On Thu Aug 21, 2025 at 7:25 PM -03, Masahiko Sawada wrote:
> What about backend processes that don't have any xid or xmin (i.e.,
> are read-only query and in idle-in-transaction)?
>
> IIUC we process the notification entries at the beginning of the
> server loop (see L4608 in postgres.c) and when reading a command (via
> ProcessClientReadInterrupt()), but it seems to me that if a process is
> in idle-in-transaction state it doesn't process the entries unless the
> transaction is committed. I've reproduced the missing clog entry error
> even if we have a notification on the queue with a valid listener,
> with the following steps:
>
Ok, now we can reproduce this, thank you! So I think that we need a way
to teach the VACUUM FREEZE about old xid's on async queue.
I'll work on this considering the initial Daniil comments at [1]
--
Matheus Alcantara
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