Re: About rollback consumption

"Howard J. Rogers" wrote:
> <<snipped>>
> When rollback segments shrink to optimal as they cross the extent boundary,
> are you saying that they can now drop extents 'behind' the direction of
> travel?

Yes. I have a very high volume system that I create rollbacks as follows:
initial 4m next 4m minextents 25 optimal 100m Then I do an alter on the rollbacks to change the next extent size to 50m. The theory behind this is to create a lot of small (4m is small for this system) rollback extents for the online transactions to use without causing undo header waits. At the same time a batch job that runs though the rollback segment and needs extents gets 50m at a time. This cut down batch time tremendously. Batch jobs were spending a lot of time waiting for rollback extents before this.

Now for your question, I very often see the rollbacks shrunk to just 3 extents after a day or two of processing. This happens when the next tran gets assigned to that rollback and all of the 4MB extents are not in use. This has happened in 7.3.4, 8.0.4, 8.0.5 and 8.0.6. I've been unable to think of a way keep the smaller extents around besides recreating the rollback segments once a week (or more often).

Big Al Received on Mon Oct 02 2000 - 19:40:26 CDT