Re: Rollback segs #/sizes?

In article <l9j76.157$ioc8.55181439_at_news.randori.com>,   Doug O'Leary <dkoleary_at_ro05-24-29-232-217.ce.mediaone.net> wrote:
>
> Hi;
>
> I tried posting this message to comp.databases.oracle.server
> about a week ago and got absolutely no responses, so I thought
> I'd try here.
>
> I'm reading through the Oracle 8i DBA Handbook and have finally
> hit the chapter on rollback segments. The book has a fairly
> involved process for identifying the correct number and sizes
> for the rollback segments. If I understand the process, it's
> as follows:
>
> 1. ID the rollback segment entry volume
> 2. ID the number of transactions
> 3. Calculate:
> a. Min possible size for each segment
> b. Min combined size for all segments
> c. Min number of rollback segments
> d. Max number of rollback segments
> 4. ID appropriate balancing act, if necessary, between
> large number of small transactions and small number of
> large transactions.
>
> That little checklist covered about 15 pages of the book. Is this
> the way it's really done in the field? I've been a UNIX admin
> for about 12 years now, most of which has been supporting Oracle
> admins. I have a hard time believing that the people I've worked
> with would have gone through all that.
>
> If this is the way it's supposed to be done, how does one go
> about identifying the number of transactions? The book suggests
> using a spreadsheet with the following headers:
>
> trans_type Number, Tot_entry_size, Avg_entry_size, largest_entry
>
> Information on the transaction type obviously comes from knowing
> your database. Number of transactions, I would think, comes from
> the delta of writes from v$rollstat. Total entry size is the product
> of number and average or largest entry size. Where does the
> average and largest entry size come from?
>
> Any info would be greatly appreciated.
>
> Doug
>
> --
> ------------------------
> Douglas K. O'Leary
> Senior System Administrator
> dkoleary_at_mediaone.net
>

I think most DBA's probably just take a pot shot at it. Since most shops are either upgrading from a prior version or have other databases in use the rbs segments have a tendency to look like what the other system's segments are set up as rather than be designed based on expectations for the new system (which is how they should always be created).

--
Mark D. Powell  -- The only advice that counts is the advice that
 you follow so follow your own advice --


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