[sulam]

You are wrong about never getting to the 99th. I did not work on this service at Twitter, but many services at Twitter are built on the JVM, and if this service is like most there, then it probably has SLA targets that are sub-millisecond at the 99th and sub 10ms at four 9's. The only caveat to this is that it has to write to disk, which may keep it from achieving truly high performance, but this is not the fault of the JVM. I worked on one service at Twitter that had to use microseconds on its dashboards just to see any variation at all throughout the day.