Re: OPTIMIZER_MODE recommendation for 9.2

Cherie,

AFAIK, ALL_ROWS tends to result in sort-merge. Good for batch processing or reporting where you want all rows returned as fast as possible.

If you are doing mainly OLTP, FIRST_ROWS is likely to be a better bet as it tends to result in a nested loops join. Good for returning the first row to the application as fast as possible.

Unless your people know something interesting about 9.2...

But check the manual at:

http://otn.oracle.com/docs/products/oracle9i/doc_library/release2/server. 920/a96533/optimops.htm#38218

(Search for response time.)

Cheers,

John Thomas

In message <F001.004AB2BA.20020805054944_at_fatcity.com>, Cherie_Machler_at_gelco.com writes
>
>Someone in our development group is recommending that OPTIMIZER_MODE be set
>to ALL_ROWS in our 9i databases. Everything that I've read recommends
>setting OPTIMIZER_MODE to choose.
>
>These are a medium-size ODS database that will have reads and writes and a
>smallish data warehouse and datamart that are going to be used mostly for
>reporting purposes.
>
>Why wouldn't I want to let Oracle choose? I think the optimizer is
>working better than ever in 9.2. Why would I want to set up the whole
>database as ALL_ROWS? Normally, I just use that as a hint in batch jobs
>or reports. Am I off-base?
>
>Thanks,
>
>Cherie Machler
>Oracle DBA
>Gelco Information Network
>
>--
>Please see the official ORACLE-L FAQ: http://www.orafaq.com

-- 
John Thomas
-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: John Thomas
  INET: john_at_toronto.demon.co.uk

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