Web Performance Tuning

Process Creation

Prior to Apache 1.3 the MinSpareServers, MaxSpareServers, and Start- Servers settings all had drastic effects on benchmark results. In particular, Apache required a “ramp-up” period in order to reach a number of children sufficient to serve the load being applied. After the initial spawning of StartServers children, only 1 child per second would be created to satisfy the MinSpareServers setting. So a server being accessed by 100 simultaneous clients, using the default StartServers of 5, would take on the order of 95 seconds to spawn enough children to handle the load. This works fine in practice on real-life servers, because they aren’t restarted frequently. But it does really poorly on benchmarks that might only run for ten minutes.

The one-per-second rule was implemented in an effort to avoid swamping the machine with the startup of new children. If the machine is busy spawning children, it can’t service requests. But it has such a drastic effect on the perceived performance of Apache that it had to be replaced. As of Apache 1.3, the code will relax the one-per-second rule. It will spawn one, wait a second, then spawn two, wait a second, then spawn four, and it will continue exponentially until it is spawning 32 children per second. It will stop whenever it satisfies the MinSpareServers setting.

This appears to be responsive enough that it’s almost unnecessary to twiddle the MinSpareServers , MaxSpareServers, and StartServers knobs. When more than 4 children ...