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RE: Job taking longer with more RAC nodes

From: <>
Date: Thu, 9 Mar 2006 17:01:14 -0800
Message-ID: <>


In looking at the tkprof output, no rows were fetched in any of the tests. This was after an even 1.2 *million* LIOs and all of this is just EXEC (rather than FETCH)? An LIO is extremely/fully CPU intensive and that is why your elapsed time is mostly taken up by cpu time. Was that a valid SQL? Also, it seems that this is a custom code.

In any case, I would assume that with RAC_ON, the kernel would go through additional code to check cross-instance buffer status and hence you suffer additional CPU usage for the same number of LIOs. (I am not a RAC expert by any measure so take this with a big pinch of salt).

John Kanagaraj <><
DB Soft Inc
Phone: 408-970-7002 (W)  

Co-Author: Oracle Database 10g Insider Solutions  

-----Original Message-----
[] On Behalf Of Hameed, Amir Sent: Thursday, March 09, 2006 1:54 PM
To: john d parker;; Subject: RE: Job taking longer with more RAC nodes

This is an Oracle 11i application 11.5.9) and the database version is (64-bit). The thing that is surprising me is that there are no RAC specific waits. It is the CPU usage that is going high. I am sure there is an explanation to this and that is what I am trying to find out.

-----Original Message-----
From: john d parker [] Sent: Thursday, March 09, 2006 4:35 PM
To: Hameed, Amir;; Subject: Re: Job taking longer with more RAC nodes

Do you have any degree of parallelism? or is parallel degree set to default?

In general, A well behaved app will perform approx the same on RAC maybe even marginally slower. A poorly behaved app will absolutely stink when moved to RAC. RAC is not a performance enhancing solution.


> Folks,
> I need some help in understanding why a job is taking longer when it
> is run in multiple nodes under RAC versus a single node in RAC and
> with RAC disabled.

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Received on Thu Mar 09 2006 - 19:01:14 CST

Original text of this message