I've been testing an Ubuntu server A running Apache/PHP using Tsung from a server B and I reached something that looks like a limit, but I can't find any idea on what it might be : here is a graph showing the behavior => https://i.stack.imgur.com/Mspqp.png The value given as max by Tsung is 1010 which doesn't look like anything I know from Apache/PHP/MySQL/Ubuntu configuration.
Server A was a virtual machine at DigitalOcean, running a simple installation of Ubuntu 12.04 and Apache2/PHP5/APC (Perfork MaxClients 384, ServerLimit 500) : usage of CPU or RAM was OK, not full. Apache's server-status page also showed open slots so the limit doesn't seem to come from there.
Server B was another virtual machine at DigitalOcean running a simple installationg of Ubuntu 12.04 and Tsung.
Webapp code included some PHP and some MySQL requests (500 max connections).
I can't find any configuration value in Apache/PHP/Ubuntu that would explain a 1000 or 1010 limit, any ideas on where to look ?