Re: undo segments online causing performance problems.

The common question was asked by all the repliers is that how do I know that undo onlie process causing the hang or slowness.

Basically, when transaction comes, we have flag called queue for different status and we see that the query is growing heavily for not process status, and when I go and check the alert.log file, exactly at the same time and second, oracle bring undo segs online. We have noticed this situation thrice comparing with undo segs online process and we determined the same.

Note:301432.1 Subject: Performance Slowdown During Heavy Undo Segment Onlining

We are exactly facing the same problem mentioned in this metalink note and as per Oracle Support advice, we also enable the event 10511, to prvent SMON taking undo segs. offline.

>
> 1. How are sure that the Onlining of the Undo segments is the cause of the
> "hang" ?
>
> 2. Do you need undo_retention at 3hours ? Have you worked out how
> much undo_retention you really need . You might be able to set it lower.
>
> At 06:02 PM Thursday, The Human Fly wrote:
> >Our share trading application database, patch set 9205, running on AIX
> >5.3 64bit with 12CPU + 30 GB Memory,. Everyday, during trading
> >beginning hours, end-users complains that the database is performing
> >very slow, like hang stage for some times. We noticed that Oracle has
> >brough many undo segs. online.
>
> Hemant K Chitale
> http://web.singnet.com.sg/~hkchital
>
>
>

--
Best Regards,
Syed Jaffar Hussain
OCP 8i & 9i DBA,
Banque Saudi Fransi,
Saudi Arabia
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