From: | Daniil Davydov <3danissimo(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Do not lock temp relations |
Date: | 2024-10-22 11:34:19 |
Message-ID: | CAJDiXgiy6H5+_ue1w-=pDNMUEnNu==U8AWR9V7vKOG0oq=jgOw@mail.gmail.com |
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On Mon, 30 Sept 2024 at 18:05, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
wrote:
> Yes. Our implementation restrictions preclude access to the contents
> of another session's temp tables, but it is not forbidden to do DDL
> on them so long as no content access is required. (Without this,
> it'd be problematic for example to clean out a crashed session's temp
> tables. See the "orphan temporary tables" logic in autovacuum.c.)
Indeed, a potentially dangerous situation may arise when both the
autovacuum and client process attempt to delete the contents of a temporary
namespace. But there is a patch (6faca9ae2878c8f642a2e5748d2dbb2b91341bec)
that protects us from race condition in this case.
--
Best regards,
Daniil Davydov
On Tue, Oct 22, 2024 at 5:55 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Maxim Orlov <orlovmg(at)gmail(dot)com> writes:
> > But for the second one: do we really need any lock for temp relations?
>
> Yes. Our implementation restrictions preclude access to the contents
> of another session's temp tables, but it is not forbidden to do DDL
> on them so long as no content access is required. (Without this,
> it'd be problematic for example to clean out a crashed session's temp
> tables. See the "orphan temporary tables" logic in autovacuum.c.)
> You need fairly realistic locking to ensure that's OK.
>
> regards, tom lane
>
>
>
>
>
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