Re: DISCARD ALL failing to acquire locks on pg_listen

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Matteo Beccati <php(at)beccati(dot)com>
Cc: Postgres Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: DISCARD ALL failing to acquire locks on pg_listen
Date: 2009-02-11 16:38:33
Message-ID: 10542.1234370313@sss.pgh.pa.us
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Matteo Beccati <php(at)beccati(dot)com> writes:
> Given I was using 8.3, it seemed quite right to set the reset statement
> to "ABORT; DISCARD ALL". Everything works fine, until a load spike
> happens and pgpool-II reset queries start to lag behind, with DISCARD
> ALL failing to acquire an exclusive locks on the pg_listen system table,
> although the application isn't using any LISTEN/NOTIFY. The reason was
> not obvious to me, but looking at the man page explained a lot: DISCARD
> ALL also performs an "UNLISTEN *".

Seems like we could/should fix UNLISTEN * to not do anything if it is
known that the current backend never did any LISTENs.

regards, tom lane

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