| From: | Mihail Nikalayeu <mihailnikalayeu(at)gmail(dot)com> |
|---|---|
| To: | Antonin Houska <ah(at)cybertec(dot)at> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Srinath Reddy Sadipiralla <srinath2133(at)gmail(dot)com>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Robert Treat <rob(at)xzilla(dot)net> |
| Subject: | Re: Adding REPACK [concurrently] |
| Date: | 2026-04-16 11:18:55 |
| Message-ID: | CADzfLwUOnargQe+rpTC5tFUOj+yNj01qJM42PAgi2CiMpZn3tw@mail.gmail.com |
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| Lists: | pgsql-hackers |
Hello!
On Wed, Apr 15, 2026 at 8:28 PM Antonin Houska <ah(at)cybertec(dot)at> wrote:
> just after step 4, the two session will probably up in a deadlock anyway. In
> other words, even if REPACK does the check early, it does not prevent other
> sessions from getting in the way.
>
> Maybe I'm still missing something.
I was trying to solve that by using another approach: the ability to
define a "future lock" [0]. It is declared even before taking the
actual lock, so, no race is possible.
That approach works correctly except one case -
ShareUpdateExclusiveLock from another backend, I described it here [1]
a little bit.
For now, I don't know how to solve it without a performance downgrade.
[0]: https://github.com/michail-nikolaev/postgres/commit/ba0f4247dad3d96b8282cd18056b7776cd69317c
[1]: https://www.postgresql.org/message-id/flat/CADzfLwU8Qw6LXFHO7Tbjc-O7o%2BtM26jdnOJBWqYLu61rf7bO%2Bg%40mail.gmail.com#1e96f8882363afb2fc53c2f08346f527
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