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Re: Important: Oracle processes taking lots of CPU

From: New DBA <>
Date: Tue, 23 Nov 2004 05:25:35 -0800 (PST)
Message-ID: <>


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 It didn't suggested or detect excess CPU/LIOs, since those stats are pretty acceptable in the trace files.


> 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

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Received on Tue Nov 23 2004 - 07:29:42 CST

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