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Consider the scale - 24 UNDO waits per day will typically be less than 0.5 seconds per day, which isn't really much of a problem.
If you have a busy system, with lots of updates and queries taking place in any 'localised' section of the database, it is almost inevitable that one process may want to rollback (for consistency) some work that was done so recently that there is a collision on active UNDO blocks. There are a number of scenarios - but if the time lost is tiny, there's no point in trying to 'fix' the issue.
-- Regards Jonathan Lewis http://www.jlcomp.demon.co.uk Next Seminar dates: (see http://www.jlcomp.demon.co.uk/seminar.html ) ____USA__________November 7/9 (Detroit) ____USA__________November 19/21 (Dallas) ____England______November 12/14 The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html Daud wrote in message ...Received on Sun Oct 27 2002 - 03:35:20 CST
>I have been monitoring v$waitstat in my production database and found
>that the count for undo header and block are increasing daily by
about
>4 and 20 respectively. What's causing this?
>
>Here is my rollback config:
>
>15 of them in a LMT tablespace with uniform extent size of 0.5Mb.
>Each rollback has minextents of 6 and each extent is 0.5Mb. Optimal
is
>not set!
>I don't see many concurrent transactions in the database. Max # of
>concurrent transactions so far is 10. They are, most of time, very
>small transactions.
>
>I believe I have seen a post from HJR somewhere in this newsgroup
>where he said he normally creates rollback segments with extent size
>of 8Mb or bigger.
>That makes me wonder whether I have got the extent size wrong.
>
>Any advice anyone?
>
>rgds
>Daud