I deactivated buffered-sql and logging directly to mysql by deafult module. Just one basic question : Buffered_SQL is single threaded module? and does not make use of available mysql threads to complete the jobs in parallel?

No, but near enough. Detail reader deliberately reads packets at a reduced rate. Authentication queries are fast - about 10x faster than accounting queries. On top of that you should aim to complete authentication as quick as possible, while if there is a delay in processing accounting data of a few seconds it's hardly going to get noticed. Imagine authentication queries as fast cars and acconting queries as a slow lorries. The idea of buffered-sql is to separate out lorries into a slow lane and leave motorway clear for fast cars to wizz by. You can increase the speed at which detail reader works but the effect of that would be to spread out lorries all over the motorway, slowing the cars down. Even if the reader gets stuck and lane with the lorries stops, the authentication will still work, and new lorries will pile up at the back of the slow lane. Once you get the lane working again, lorries will be on their way, again with no impact to authentication (cars). Ivan Kalik Kalik Informatika ISP