Hey Alec, This looks like a tricky problem. Have you looked at the traffic using tcpdump or ethereal when the machine hangs? You might also try out mod_forensic or mod_security and add mod_security internal timestamps to the access-log. Using these logs you will get a clearer idea where it hangs. How does your apache look memory-wise in top/htop? Are you sure it is not an application issue - even if it shows serving static files. A reverse proxy setup for testing purposes could seperate application and static file serving to give you a clearer idea in this regard. These are just a lot of ideas. I do not really know how to solve your problem, but this would give you a clearer idea of the problem. I am not familiar with best practice values for MaxMemFree. regs, Christian On Sun, Sep 30, 2007 at 03:54:59PM -0700, 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 10s to serve a 1K > thumbnail. > It is usually correlated with load spikes, but not perfectly (by looking at > the bandwidth graph) > Then it requires a stop/start, and it becomes fast again. > This has been happening before, and it was always accompanied with > > [error] server reached MaxClients setting, consider raising the MaxClients > setting > > in the apache log. > > We raised MaxClients from 200 to 300, and now it happens with no warning > in any logs at all, except with the usual > > web10 kernel: possible SYN flooding on port 80. Sending cookies. in > /var/log/messages (this has always happened when apache hung from overload). > > What worries me is that there are no log messages in apache logs at all when > this happens. > > This is the relevant part of httpd.conf > > ServerLimit 300 > # we are using prefork MPM > <IfModule prefork.c> > StartServers 10 > MinSpareServers 5 > MaxSpareServers 20 > MaxClients 300 > MaxRequestsPerChild 10000 > MaxMemFree 2560 > </IfModule> > > The server has 4GB of RAM and 4GB of swap. When apache "crashes" i.e. > becomes very slow, the swap size is still 0 and vmstat shows no swapping. > I suspect the problem may be in > > MaxMemFree 2560 > > but then I would expect some kind of "out of memory" errors in the logs? > Another question: what is the good choice of MaxMemFree value? We want to > leave 512MB-1GB or RAM on this machine for other tasks. > > > > > > --------------------------------------------------------------------- > The official User-To-User support forum of the Apache HTTP Server Project. > See <URL:http://httpd.apache.org/userslist.html> for more info. > To unsubscribe, e-mail: users-unsubscribe@xxxxxxxxxxxxxxxx > " from the digest: users-digest-unsubscribe@xxxxxxxxxxxxxxxx > For additional commands, e-mail: users-help@xxxxxxxxxxxxxxxx > --------------------------------------------------------------------- The official User-To-User support forum of the Apache HTTP Server Project. See <URL:http://httpd.apache.org/userslist.html> for more info. To unsubscribe, e-mail: users-unsubscribe@xxxxxxxxxxxxxxxx " from the digest: users-digest-unsubscribe@xxxxxxxxxxxxxxxx For additional commands, e-mail: users-help@xxxxxxxxxxxxxxxx
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