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From "Alec Matusis" <matu...@yahoo.com>
Subject RE: 2.0.54 unstable, requests time-out, NO warnings in logs
Date Mon, 01 Oct 2007 08:36:28 GMT
> Have you checked without the MaxMemFree setting?
I raised MaxMemFree to 3100, we will have to wait for a few days, since it
does not happen every day.

> Why do you use MaxMemFree with such a small value at all?

We are also running 2 twistd server processes on this machine that can take
up to 256MB each, so we wanted to leave some room for them.

As I understand from the manual, MaxMemFree is not an absolute limit on the
memory available to Apache anyway, it just asks it to release *unused*
memory with free() call after it reaches MaxMemFree value? 

> -----Original Message-----
> From: Ruediger Pluem [mailto:rpluem@apache.org]
> Sent: Monday, October 01, 2007 1:23 AM
> To: dev@httpd.apache.org
> Subject: Re: 2.0.54 unstable, requests time-out, NO warnings in logs
> 
> 
> 
> On 10/01/2007 08:32 AM, Alec Matusis wrote:
> > We are running a busy Apache/2.0.54 server on 2.6.9 kernel, that
> suddenly becomes very slow- requests either time out, or it takes 10-
> 20sec to serve a 1K thumbnail.
> > It is somewhat correlated with load spikes, but not perfectly (by
> looking at the bandwidth graph, it never happens during the low
> bandwidth periods at night, but it does not coincide with peaks of b/w)
> >
> > When we initially encountered an apache overload, it was always
> accompanied with
> >
> > [error] server reached MaxClients setting, consider raising the
> MaxClients setting
> >
> > in the apache error log. We also got
> >
> > kernel: possible SYN flooding on port 80. Sending cookies.
> >
> > in /var/log/messages system log.
> >
> > After that I raised MaxClients from 200 to 300. The problem initially
> disappeared, but after our bandwidth grew a bit more, we got this
> behavior again.
> > Now apache crashes (becomes very slow) silently, with no warning in
> apache error logs at all (although we still get SYN flood message in
> the system log)
> > When apache is this 'slow' regime, /server-status still shows
> available slots, i.e. MaxClients is not reached.
> >
> > This is the relevant part of httpd.conf:
> >
> > ServerLimit 300
> > # we are using prefork MPM
> > StartServers 10
> > MinSpareServers 5
> > MaxSpareServers 20
> > MaxClients 300
> > MaxRequestsPerChild 10000
> > MaxMemFree 2500
> >
> > The server has 4GB of physical RAM and 4GB of swap. During these
> apache “slowdowns", the swap size is still 0 and vmstat shows no
> swapping at all.
> > I suspect the problem may be in
> >
> > MaxMemFree 2500
> 
> Have you checked without the MaxMemFree setting?
> Why do you use MaxMemFree with such a small value at all?
> 
> Regards
> 
> Rüdiger


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