I'm trying to increase the speed of inserts in a database that is on a not super fast storage system. I have installed a pair of SSDs and placed pg_xlog on them but am still getting inserts that take up to a second to complete, with .3 seconds being about average. Iostat doesn't show the SSDs stressed at all, and changing synchronous_commit doesn't seem to affect it one way or the other. Where would I look next for what could be causing the delay?