| From: | Matheus Alcantara <matheusssilv97(at)gmail(dot)com> |
|---|---|
| To: | Rishu Bagga <rishu(dot)postgres(at)gmail(dot)com> |
| Cc: | Arseniy Mukhin <arseniy(dot)mukhin(dot)dev(at)gmail(dot)com>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, 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>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Joel Jacobson <joel(at)compiler(dot)org> |
| Subject: | Re: LISTEN/NOTIFY bug: VACUUM sets frozenxid past a xid in async queue |
| Date: | 2025-09-05 10:44:11 |
| Message-ID: | CAFY6G8f0JEF3HE4Q+ZZYjpPiFfRREzJ+r6zbJh2ZUFb2jhqm7g@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed Sep 3, 2025 at 8:51 PM -03, Rishu Bagga wrote:
> On Wed, Sep 3, 2025 at 2:14 PM Matheus Alcantara
>
> <matheusssilv97(at)gmail(dot)com> wrote:
>
>
>> IIUC we don't store notifications of aborted transactions on the
>
>> queue. On PreCommit_Notify we add the notifications on the queue
>
>> and on Commit_Notify() we signal the backends.
>
>>
>
>> Or I'm missing something here?
>
>
> My understanding is that something could go wrong in between
>
> PreCommit_Notify and AtCommit_Notify, which could cause the
>
> transaction to abort, and the notification might be in the queue at
>
> this point, even though the transaction aborted, hence the dependency
>
> on the commit log.
>
Ok, I agree that that this may happen but I don't see this as a common
case to fix the issue based on this behaviour. I think that we check the
transaction status also to skip notifications that were added on the
queue by transactions that are not fully committed yet, and I see this
scenario as a more common case but I could be wrong.
--
Matheus Alcantara
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