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From: Christophe Pettus <[email protected]>
To: Costa Alexoglou <[email protected]>
Cc: [email protected]
Subject: Re: Vacuum full connection exhaustion
Date: Thu, 8 Aug 2024 07:11:21 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAJ+5Ff6WtFCzamrRZqN3u3htvkGcmob7VaYWYBd+sRx6jKpHuA@mail.gmail.com>
References: <CAJ+5Ff6WtFCzamrRZqN3u3htvkGcmob7VaYWYBd+sRx6jKpHuA@mail.gmail.com>



> On Aug 7, 2024, at 10:34, Costa Alexoglou <[email protected]> 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.





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