Pinba
Pinba is a statistics server for PHP using MySQL as a read-only interface.\nIt accumulates and processes data sent over UDP by multiple PHP processes and displays statistics in a nice human-readable form of simple "reports", also providing read-only interface to the raw data in order to make possible generation of more sophisticated reports.\nWith Pinba extension users also can measure particular parts of the code using timers with arbitrary tags.\nPinba is not a debugging tool in a common sense, since you're not supposed to do debugging on production servers, but its main goal is to help developers to locate bottlenecks in realtime and direct developers' attention to the code that really needs it.