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From: Costa Alexoglou <[email protected]>
To: David Rowley <[email protected]>
Cc: Christophe Pettus <[email protected]>
Cc: [email protected]
Subject: Re: Vacuum full connection exhaustion
Date: Fri, 9 Aug 2024 11:47:26 +0200
Message-ID: <CAJ+5Ff4n+3SpSeDGd1UwF7JyvBkgHi7uyz0i+JtisD1m0U-PbQ@mail.gmail.com> (raw)
In-Reply-To: <CAApHDvrLiwiB8o+3R2M4JbwyovhD7Btt0h=+8_d85Lt+oxoy7Q@mail.gmail.com>
References: <CAJ+5Ff6WtFCzamrRZqN3u3htvkGcmob7VaYWYBd+sRx6jKpHuA@mail.gmail.com>
	<[email protected]>
	<CAApHDvrLiwiB8o+3R2M4JbwyovhD7Btt0h=+8_d85Lt+oxoy7Q@mail.gmail.com>

On Fri, Aug 9, 2024 at 1:02 AM David Rowley <[email protected]> wrote:

> On Fri, 9 Aug 2024 at 02:12, Christophe Pettus <[email protected]> wrote:
> > 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 also imagine this is the cause. One way to test would be to do:
> BEGIN; LOCK TABLE <name of table>; and see if the connections pile up
> in a similar way to when the VACUUM FULL command is used.
>
> David
>

Thanks folks. David really straight-forward way to test. I validated this,
when I lock the two tables involved in the benchmark the connections are
constantly growing until they reach the `max_connections`

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