Tony, Yes if Oracle is not waiting but working no wait will be registered. But it should atleast be reflected in "CPU used by this session" stat. It doesn't. I traced a few processes, but the trace files show no SQL which takes lots of CPU. Moreover, the CPU utlization in the trace file, or in v$sesstat don't match with the actual CPU taken by the process as seen from the OS commands like "top" Thats why I believe its some kind of O/S issue. So I did a truss on the process. And I saw the following line repeating infinitely. select(2048, 0x800003fffdffb3d0, 0x800003fffdffb4d0, 0x800003fffdffb5d0, 0x800003fffdffb6d0) = 0 I'm not sure how to interpret the output of truss, so I posted it in this forum since there are many experts out here, who might be able to interpret it! Is there any further information I can gather at the O/S level which throws some light on the problem? As far as statspack is concerned, we haven't implemented statspack, but I did run utlbstat/utlestat and uploaded the output to oraperf.com. It didn't suggested or detect excess CPU/LIOs, since those stats are pretty acceptable in the trace files. Regards New DBA --- Tony.Adolph@xxxxxx wrote: > I'm no expert here, but here *may be* a few things > to think about: > > When Oracle is actually doing something it isn't > recorded as a wait event, > e.g. getting a datablock that is in cache doesn't > generate a wait event. > If your query is "horrible" you could be using loads > of CPU without > generating many waitevents. > > A little more dodgy info: "db file sequential > read" is normally > accociated with datafile access by rowid, ie. after > an index lookup. > > I think I'd try to find out which queries are > running during the > performance problem times and explaining the > queries. > > Also, have you run spreport for this time period? > > Told you I wasn't an expert, but I hope that prompts > other readers to fill > in the gaps and give you better hints, > > Good luck > Tony __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -- //www.freelists.org/webpage/oracle-l