Re: Vacuum full connection exhaustion

On Thu, Aug 8, 2024 at 10:12 AM Christophe Pettus <xof(at)thebuild(dot)com> wrote:

>
>
> > On Aug 7, 2024, at 10:34, Costa Alexoglou <costa(at)dbtune(dot)com> wrote:
> >
> > Hey folks,
> >
> > I noticed something weird, and not sure if this is the expected
> behaviour or not in PostgreSQL.
> >
> > So I am running Benchbase (a benchmark framework) with 50 terminals (50
> concurrent connections).
> > There are 2-3 additional connections, one for a postgres-exporter
> container for example.
> >
> > So far so good, and with a `max_connections` at 100 there is no problem.
> What happens is that if I execute manually `VACUUM FULL` the connections
> are exhausted.
>
> VACUUM FULL takes an exclusive lock on the table that it is operating on.
> It's possible that a connection becomes blocked on that exclusive lock
> waiting for the VACUUM FULL to finish, the application sees the connection
> stopped and fires up another one (this is common in container-based
> applications), that one blocks... until all of the connections are full of
> queries waiting on that VACUUM FULL.
>
>
"I see a lock, so let's cause another one!" That's crazy.

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