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Re: Do I really need more than 1 rollback segment?

From: Cyber Office <jcheong_at_cooper.com.hk>
Date: 15 Dec 2001 07:17:44 GMT
Message-ID: <9veteo$8061@imsp212.netvigator.com>


An interesting example of building a 3 TB Oracle database for TPC-H benchmark. There are totally 800 rollback segments in the benchmark.

http://www-4.ibm.com/software/data/highlights/db2leads-o3tb-details.html

http://www-4.ibm.com/software/data/highlights/db2leads-o3tb.html

Personally, I think 1 rollback segment is not enough.

Wed, 12 Dec 2001 06:38:29 +1100 Howard J. Rogers <dba_at_hjrdba.com> wrote:
> We could have a battle of the giants on our hand here. Steve Adams says
> make 'em big, and who cares about a bit of wasted space: these things are
> supposed to be on their own hard disk anyway. (I am paraphrasing like
> crazy, natch).
>
> Personally, I go for the Steve Adams school of thought on this one. I can't
> see any drawbacks (though I'm sure Jonathan will elaborate on the
> 'additional I/O' idea) of large segments. It's the NUMBER of them that's
> the worry, to avoid contention issues.
>
> As for sizing them "appropriately" -you must have the best behaving set of
> Users I've never met. It takes just one of them to raise a transaction and
> leave it uncommitted, and growth will follow as sure as day follows night.
> The more "appropriate" your segments are for daily use, the more such growth
> will be required in such circumstances. And that's the reason I *still*
> wouldn't touch optimal with a bargepole.
>
> Regards
> HJR
> --
> ----------------------------------------------
> Resources for Oracle: http://www.hjrdba.com
> ===============================
>
>
> "andrew_webby at hotmail" <andrew_webby_at_hotmail.com> wrote in message
> news:f45d9b0.0112110438.414536d_at_posting.google.com...

>> Just as a 'further', I knew I'd picked up that "rule of thumb"
>> somewhere and as in my previous post, it was when I posted my
>> statspack report some time back.
>>
>> From Johnathan Lewis:
>>
>> "As already appreciate, your rollback segments
>> seem to be much too big for activity shown, and
>> the optimal is too high -  little known rule of thumb,
>> rollback segments should be as small and as few
>> as possible to reduce redundant I/O.  In your case
>> the size of the rollbacks doesn't seem to have
>> resulted in any significant I/O cost."
>>
>> I'm sure his meaning was not to set them incredibly small as I
>> appeared to be suggesting, but more to size them appropriately.
>> Comments appreciated.
>>
>> Andrew
>>
>> "Howard J. Rogers" <dba_at_hjrdba.com> wrote in message

> news:<3c110a2a$0$29051$afc38c87_at_news.optusnet.com.au>...
>> > I agree with your disagree!  Setting rollback segments 'as small as you

> can
>> > make them' is just plain daft, and setting optimal at all is equally

> mad.
>> > Optimal is there for those databases that don't have a full-time DBA,

> and as
>> > such it can be a useful 'light-weight management' tool.  But in a
>> > properly-managed production database, it's an utterly lousy idea.
>> >
>> > Regards
>> > HJR
>> > --
>> > Resources for Oracle: http://www.hjrdba.com
>> > ===============================

>
>
-- 
http://www-902.ibm.com/hk/sme/corner/solution_detail.html#a3
http://www.attunity.com
Received on Sat Dec 15 2001 - 01:17:44 CST

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