Re: Undo header wait

From: Mike F <u518615722_at_spawnkill.ip-mobilphone.net>
Date: Sat, 16 Feb 2002 01:49:01 GMT
Message-ID: <l.1013824141.1606170654@pool-151-197-235-40.phil.east.verizon.net>

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  

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Received on Fri Feb 15 2002 - 19:49:01 CST