Re: Poor Performance of undo space management in 10.2 - bug info

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Date: Wed, 13 Feb 2008 11:34:59 -0500
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Thank you very much for very useful information.

Mayen Shah

"John Hallas" <>
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Feb 13 2008 11:18 AM
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"oracle-l" <>


Poor Performance of undo space management in 10.2 - bug info

This note is a heads-u on a bug which has caused me some problems over the last few days and yet is easily identifiable and resolvable (once you recognize the issue).    

We have spent the last 2 days trying to run a benchmark to prove end to end performance of a new code set. We have been plagued by undo tablespace problems which had the following symptons :-  

Rapid growth of used undo tablespace
Serious deterioration in performance as the undo tablespace got very full Loss of application connectivity as responses were not received in time (trading system with about 7 servers being used to hold components of the system)  

The complex set up of the test rig tended to mask the database aspect on each run and it was only this morning that we really focused on the undo tablespace.  

We had AUM set and a 60 second retention period and various sized t/s using both Ramsan and local disk.  

The problem was identified as undo extents remaining marked as unexpired well past the retention period, despite all connections being terminated and no active transactions running.
Searching on Metalink showed Note 5387030.1 which refers to a bug with the TUNED_UINDORETENTION setting. This can be seen in v$undostat and once we had run alter system set "_smu_debug_mode" = 33554432; the v$undostat.tuned_undoretention statistic dropped from 345600 to 2188 and performance improved with unexpired undo segments hardly rising despite heavy throughput.  

This bug is common through 10.2.01 to or is fixed in or V11.  


+44 (0)113 223 2274 (direct)
+44 (0)113 297 9797  

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Received on Wed Feb 13 2008 - 10:34:59 CST

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