Message-ID: <148578d8112ccef38ba0199bebf0fbcb358f200d.camel@cybertec.at>
Subject: Re: client_connection_check_interval default value
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Tom Lane <tgl@sss.pgh.pa.us>, Fujii Masao <masao.fujii@gmail.com>
Cc: Jeremy Schneider <schneider@ardentperf.com>, Jacob Champion	
 <jacob.champion@enterprisedb.com>, "pgsql-hackers@lists.postgresql.org"	
 <pgsql-hackers@lists.postgresql.org>, Marat Buharov
 <marat.buharov@gmail.com>,  Greg Sabino Mullane	 <htamfids@gmail.com>,
 Thomas Munro <thomas.munro@gmail.com>
Date: Fri, 06 Feb 2026 10:40:02 +0100
In-Reply-To: <1667818.1770336112@sss.pgh.pa.us>
References: <20260204213032.15bab46b@ardentperf.com>
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	 <20260205150452.00006167@ardentperf.com>
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On Thu, 2026-02-05 at 19:01 -0500, Tom Lane wrote:
> Fujii Masao <masao.fujii@gmail.com> writes:
> > On Fri, Feb 6, 2026 at 8:05=E2=80=AFAM Jeremy Schneider
> > <schneider@ardentperf.com> wrote:
> > > I did see a real system outage that could have been prevented by an
> > > appropriate default value here, since I didn't yet know to change it.
>=20
> > I'm not sure that client_connection_check_interval needs to be enabled
> > by default.
>=20
> I think enabling it by default is a nonstarter, because it changes
> behavior in a significant way.  Specifically, it's always been the
> case that if the client disconnects during a non-SELECT query (or
> anything that doesn't produce output), the backend would complete that
> query before ending the session.  I think it's very likely that there
> are users depending on that behavior.

*Perhaps* there are some users who depend on the current behavior, but
my experience is that the vast majority of users don't want that statements
started by a connection that went dead should keep running.

I mean, it would be a change in behavior, but that is normal during a
major upgrade, and users who actively want the current behavior can
disable client_connection_check_interval.

I think that enabling client_connection_check_interval would be a net win,
as far as the core functionality is concerned.

Fujii Masao's concern that log_lock_waits would issue a message every
client_connection_check_interval is much more serious in my opinion, now
that log_lock_waits is enabled by default (at - erm - my insistence).

Why does the deadlock detector kick in every client_connection_check_interv=
al?

Yours,
Laurenz Albe