Re: sizing of rbs

Phil Roberts (proberts_at_iglou.iglou.com) wrote:
: hack_at_netcom.com (Elaine Hacklander) writes:
 

: >Is there some equation for the sizing of rollback
: >segments? I am currently creating specs for a
: >system in which disk space is at a premium and
: >the base configuration cannot be modified.
 

: As Elaine wrote, I too have a system where free space and
: partitions are at a very minimum. We are trying to figure
: out how large we should make our tablespaces. Is there a
: formula someone could post that would allow us to figure
: how large to make our tablespaces when we convert a database
: to 6.0.27 from 5.(something)? Our tables won't grow much
: larger than they currently are in the version 5 DB. We
: know how many rows and columns we will have, so if we could
: have some sort of calculation we would know what sizes to
: use with the create statements.

Table(space) and rollback sizing are 2 completely different issues. Table sizing is easy - there's a formula in the ORACLE7 Administration guide. That formula also is valid for version 6. The formula in the V6 DBA Guide is bogus. I've written an Excel5 spreadsheet that'll do all this for you. If someone can tell me how i can post it (or email it) i'd be happy to share it.

Rollback segments are another bag of worms entirely. A large batch update will require one large one. Transaction processing will usually be served best by multiple, smaller ones. Some people take the middle of the road approach, others have 2 sets of rollback segs, and recycle the db depending on which set they need. ORACLE7 can help here, because it allows you to specify an optimal rbs size. Once you figure out a strategy, you'll probably need to do some tuning here with the number and size.

I'd also recommend re-reading the manual on these topics.

Barry Received on Sat May 07 1994 - 20:16:02 CEST