Re: Rollback Segment Question

>From your post the "undo header contention" statistic seems to indicate
that you have an issue with the number of rollback segments available. Some contention is perfectly acceptable and to be expected on any real world database. The first question is what percentage of RBS segments results in contention.

If the percentage is high enough to worry about then being that the rollback segment header blocks are most likely cached in the buffer pool you probably should add 3 more rollback segments and compare statistics to see if the additional segments result in an appropriate reduction in contention rather than move the segments to a different disk setup. While RAID 10 is generally better for performance than RAID 5 it is not the problem so the move will not truely solve eliminate the contention problem though faster IO might result in some relief. Nevertheless if you have more active transactions than RBS segments then transactions have to share segments and if you get multiple heavy hitters assigned to the same segment then some contention is bound to result. Again some contention is to be expected.

HTH -- Mark D Powell -- Received on Wed May 25 2005 - 09:01:25 CDT