Subject: Re: postfix broken by AF_LOCAL semantics change
To: None <tech-kern@NetBSD.org>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
Date: 11/29/2003 16:07:17
>> Could you please elaborate on the need?
> If connect succeed with any backpressure (as is the default
> behavior), then it quite easy for a swarm of requests to overwhelm an
> accepting server since his backlog can be exceeded before he even
> gets scheduled to run.
This can happen even with block-until-accept behaviour; it just takes
lots of processes. Which is probably what you would have anyway; how
often does a single process connect to the same server again before
carrying out whatever protocol the first connection is intended for?
> If you make the connect sleep until accepted, you can limit the
Only by the number of client processes. And even then, only if the
clients are using blocking-mode connects; if the clients are using
nonblocking connects, you are either breaking nonblocking connect
semantics or not helping any.
> Part of the problem is that when the backlog is exceeded the error is
> ECONNREFUSED. This makes it impossible for a client to determine
> whether it was because there was no socket bound to the right name or
> that socket accept queue became full.
Right. So maybe the right thing to do is to fix that. Or increase the
silent hard limit on listen queue length.
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