Re: Looking for pointers in troubleshooting -> RAC performance degradation (single instance is fine)

Are you doing a lot of inserts/updates to tables that have indexes that are populated by sequences? You should find the objects the contention is on. To assist with this, take a look at this page. http://www.ardentperf.com/2007/09/12/gc-buffer-busy-waits-in-rac-finding-hot-blocks/

Basically what "could" be happening (what happened with me) was that I had a bunch of sessions across nodes all fighting to put entries into the same index blocks. Even on one node, this would be a contention issue. What I did to fix my issue was identify the indexes with the contention and made them reverse key indexes. With reverse key indexes you lose the ability to perform certain operations like an index range scan. So if you do queries where something is between this value and that value etc, it might be the right solution for you.

Good Luck.

On Thu, Dec 24, 2009 at 8:28 AM, Pradeep Chetal < Pradeep.Chetal_at_mformation.com> wrote:

>
>
> Folks,
>
>
>
> We have an app that is running well in single instance but when put on a
> 2-node or 3-node RAC, we see pretty much similar performance. However, if
> the CPU time is 55-60% in single instance, it becomes 20% in 3-node RAC and
> top-5 itmed events become..
>
>
>
> "gc buffer busy", "gc current block busy", "enq: TX- index contention
>
>
>
> Any help in what to look for will be greatly appreciated.
>
>
>
> Thanks,
>
>
>
> -- Pradeep
>
> *Pradeep Chetal*
> Sr. Director - Infrastructure Architecture
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-- 
Thomas Roach
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