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Date: Thu, 11 Jul 2013 09:19:40 +0200
From: Andre Oppermann <andre@freebsd.org>
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To: Andriy Gapon <avg@FreeBSD.org>
Subject: Re: Listen queue overflow: N already in queue awaiting acceptance
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On 11.07.2013 09:05, Andriy Gapon wrote:
> kernel: sonewconn: pcb 0xfffffe0047db3930: Listen queue overflow: 193 already in
> queue awaiting acceptance
> last message repeated 113 times
> last message repeated 518 times
> last message repeated 2413 times
> last message repeated 2041 times
> last message repeated 1741 times
> last message repeated 1543 times
> last message repeated 1283 times
> last message repeated 1178 times
> last message repeated 1020 times
> ...
>
> What does this messages mean?

That your server process lagging behind in accepting new connections and a
quite a number of them get aborted due to a backlogged listen queue.

Making the accept queue longer doesn't help, it's user-space that can't keep
up with the rate of new incoming connections.

You can either reduce the rate of new incoming connections, optimize your
server process to accept more connections in the same time, or get a beefier
machine.

> Is it really that important to be printed?

The log messages are at DEBUG level.  People probably want to know about
their server not keeping up and throwing incoming connection attempts away.

> Finally, why is it not throttled?

The frequency it happens with is important to determine if this is only
a temporary spike (micro-burst) or persistent condition.

-- 
Andre