The Twitter Engineering team (@twittereng) has just achieved an impressive 3x performance improvement for Twitter search queries, largely, it seems, by replacing Ruby-on-Rails web applications with new applications built on Java, coupled with a switch from MySQL to Lucene for the data store.

This post provides some much-needed clarity on the subject of HTTP server load, and demonstrates how to calculate the key metrics which allow system architects to plan capacity and estimate the scaling needed for a system.