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From: Laurenz Albe <[email protected]>
To: Tom Lane <[email protected]>
To: Fujii Masao <[email protected]>
Cc: Jeremy Schneider <[email protected]>
Cc: Jacob Champion <[email protected]>
Cc: [email protected] <[email protected]>
Cc: Marat Buharov <[email protected]>
Cc: Greg Sabino Mullane <[email protected]>
Cc: Thomas Munro <[email protected]>
Subject: Re: client_connection_check_interval default value
Date: Fri, 06 Feb 2026 10:40:02 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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	<[email protected]>
	<CAHGQGwHZUmg+r4kMcPYt_Z-txxVX+CJJhfra+qemxKXvAxYbpw@mail.gmail.com>
	<[email protected]>

On Thu, 2026-02-05 at 19:01 -0500, Tom Lane wrote:
> Fujii Masao <[email protected]> writes:
> > On Fri, Feb 6, 2026 at 8:05 AM Jeremy Schneider
> > <[email protected]> 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.
> 
> > I'm not sure that client_connection_check_interval needs to be enabled
> > by default.
> 
> 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_interval?

Yours,
Laurenz Albe

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