Until now, our methods and tools to measure performance are quite blunt—we can see how fast our Lighttpd is with a specific optimization, but we do not know where to start. Ahmdahl's law (see http://en.wikipedia.org/wiki/Amdahl%27s_law) implies that if we optimize a portion of the code that takes up a portion X of the time by the ratio Y, the resulting speedup is limited by X. The downside of this is optimizing code that never gets called which is a good way to throw away our time. The upside is that if we know which portions of the code takes up most of the time, we know where to optimize.

A crude way of finding out where Lighttpd spends its time (at least between reading and writing) is log timing. As of Lighttpd 1.5.0, there is a new configuration option: debug.log-timing. This option can be enabled to insert timing information into the log files. For each request, the start time plus three intervals will be timed. The interval between receiving and queuing the request...