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Re: Undo header wait

From: Svend Jensen <Master_at_OracleCare.Com>
Date: Sun, 17 Feb 2002 13:05:41 +0100
Message-ID: <3C6F9C95.7030106@OracleCare.Com>


Mike F wrote:

> After tried Howard Rogers's three suggestions, I still get the same
> amount of undo header waits, and it all happens at the same time, one
> hour difference.
>
> time event waits
> 2-15-2002 02:21 undo header 8
> 2-15-2002 02:22 undo header 6
> 2-15-2002 03:22 undo header 10
> 2-15-2002 03:24 undo header 9
> 2-15-2002 04:23 undo header 12
> 2-15-2002 04:26 undo header 8
> 2-15-2002 05:25 undo header 4
> 2-15-2002 05:26 undo header 6
> ..........
>
> I came across the same problem form Ixora web, but they did not
> provide the solution, could somebody tell me what do they mean and how
> should we deal with the problem?
>
> Thanks
>
> Q: Even I have over 12 rollback segments and the max concurrent
> transaction is 4, I still get some undo header and undo block waits
> from V$WAITSTAT. Is it possible to increase the FREELIST or FREELIST
> GROUP for those rollback segments to alleviate this problem just like
> what we do for normal tables or data segments?
>
> A:There are no such tuning options for rollback segments. This is
> probably a problem with failing to retain undo blocks in cache for long
> enough after they have been modified.
>
> How should we keep the undo blocks in cache for long enough? increase
> db_block_buffer? But our hit ratio is very good. I am really confused
> here.
>
> Thanks
>

Are you suffering a large performance decrease from this,

or are you just trying to get your ratios to look nice?

Waiting is not bad, if waits are short. All depending on what you are dooing. Some process running every hour, dooing extreeme commit dance, beating the system?
/svend jensen Received on Sun Feb 17 2002 - 06:05:41 CST

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