Re: Rollback Segs

kal121_at_yahoo.com wrote:

> I am creating 10 rollback segs, initial extent 50K, next extent 50K.
>
> My question is, is it better to set maxexents UNLIMITED, and set
> the OPTIMAL to some value to provide shrinkage

How big are your transactions? Do you know that each transaction will fit in a 50k extent? Do you know that your tablespace is big enough to hold all simultaneous transactions? Do you expect "unusual" transactions?

I don't particularly like OPTIMAL, as that means (based on the documentation I've read) that the segments are constantly growing and shrinking as load changes.

I would start by making each extent large enough to hold the largest "expected" transaction. For example, our application has one transaction that will write 1-2 blocks to each of 10 tables. This means that a rollback extent has to be at least 160k (2 x 10 x 8k); I use 256k because I like round numbers.

Then create a rollback tablespace large enough to hold one of those transactions from each of your clients, and add some free space.

Then run your system, and use Bstat/Estat to monitor actual rollback segment use; you may need runs of days or more. Look to see if your rollbacks have reached a steady state and are balanced. If not, figure out why.

If you have the occasional large transaction, either create a special rollback segment for it or be prepared to manually shrink your existing segments.

-kdg Received on Fri Nov 13 1998 - 13:38:21 CST