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
