[OSM-talk] Linuxtag demonstration down - Re: handover of tile.openstreetmap.org

[Jon Stockill]

Nick Hill wrote:
> Hi Jon
> 
> I looked at apache2.conf.
> 
> # prefork MPM
> # StartServers ......... number of server processes to start
> # MinSpareServers ...... minimum number of server processes which are kept spare
> # MaxSpareServers ...... maximum number of server processes which are kept spare
> # MaxClients ........... maximum number of server processes allowed to start
> # MaxRequestsPerChild .. maximum number of requests a server process serves
> <IfModule prefork.c>
> StartServers        10
> MinSpareServers     10
> MaxSpareServers     20
> MaxClients          60
> MaxRequestsPerChild  100
> </IfModule>
> 
> 
> I reckon changing maxclients to 20 may help.
> 
> With the settings above, 60 apache processes could start. We could have 40 
> processes being launched then being immediately killed as the load shoots up and 
> down. This can be very resource intensive. Apache tends to queue http requests 
> anyway until an http process can handle them.

The easiest way to tune that is to look at how much ram everything but 
apache is using - work out how much you have to play with, then divide 
this available ram figure by the average size of your apache process - 
the number you arrive at is the number of max clients you should get 
away with before driving the machine into swap - at which point 
performance goes down the pan.

That gives you a good starting point - obviously if there are apache 
modules you're not using they should be disabled to reduce the memory 
footprint and increase the number of instances you can run. If the tasks 
are particularly cpu intensive you may find that you need to reduce the 
number of processes anyway as you'll hit CPU limits before you run out 
of ram.

-- 
Jon Stockill
lists at stockill.net