More than a year we're using the same VPS server's provider. We set about 10 web sites live on these servers and never had similar problem before. One of the web sites crashed recently and the only way to bring it back to live was to reboot it through vps panel. Apache error.log recorded an error message saying 'MaxClients limit reached'. I didn't manage to find the exact cause of this particular crash. Number of visitors should not be too high on the web site (we get more traffic on previous web sites which are based on the same configuration). I increased MaxClients setting slightly from 150 to 200 and we haven't got a similar crash since, which is over 2 months now. I don't know however, if that's the result of increasing MaxClients value I've done some basic benchmarking of the server with AB. Testing simple html file gave nice results of over 1500 requests per second. However, testing the homepage, which is the most 'busy' part of the website, gave results of 8 request per second... see below Homepage of the web sites sends 7 requests on load, while most of the subpages between 2-5 requests. Is there any simple way I can calculate, based on these results, approximate number of users the web site will be able to handle at one time? Can you see any relevance between the results and the MaxClients limit reached error and server crash?