RE: 9i - ASSM

From: Koivu, Lisa <Lisa.Koivu_at_Cendant-TRG.com>
Date: Fri, 5 Mar 2004 10:37:09 -0500
Message-ID: <840C139B79E7CC4496B2594E9E35E967046C5573@floexmailbe2.ffci.com>

Jonathan, can you expand on the bugs you reference and how the CBO is fooled? We have the same debate going on here.

If you have bug numbers and a nice example of the CBO choking, that would be very helpful.

Thank you
Lisa Koivu
Orlando, FL, USA

-----Original Message-----
From: Jonathan Lewis [mailto:jonathan_at_jlcomp.demon.co.uk] Sent: Friday, March 05, 2004 3:33 AM
To: oracle-l_at_freelists.org
Subject: Re: 9i - ASSM

"Oracle features are like fine wines - they should be allowed to mature for a few years before you try them"

(Tom Kyte - re-interpreting the commonest reason he had heard for people avoiding new features).

On this one, my sympathies lie with your senior DBA.

I know that there are bugs with ASSM, and I know that there are types of behaviour that will hit them.
ASSM blows the CBO's basic index cost calculations apart, so if you don't know what's going on, you can waste a lot of time "fixing" code that doesn't need fixing. I wonder if this is a good reason for waiting until you go to v10 to use ASSM - perhaps the optimizer has been clued in to the side effects in that version.
ASSM is supposed to fix issues with concurrency, in particular for RAC - but it's very hard to build and execute proper concurrent tests; so the possibility of finding bugs in a development environment is small. Rememebr - when you do data loading for testing, you will have to load the data AS IF it were coming in from real users, otherwise you're not doing the test in a fashion that represents what's going to happen.

On the other hand, ASSM is clearly the strategic direction for Oracle - so at some stage you'll have to go with the flow. You could compromise - by testing in production - design you tablespace strategy with a view to being able to move objects from freelist to assm (and back again) with minimum pain, a few at a time.

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html

March 2004 Hotsos Symposium - The Burden of Proof Dynamic Sampling - an investigation
March 2004 Charlotte OUG (www.cltoug.org) CBO Tutorial April 2004 Iceland
June 2004 UK - Optimising Oracle Seminar

Original Message ----- From: "Mark Moynahan" <Mark.Moynahan_at_apollogrp.edu> To: <oracle-l_at_freelists.org> Sent: Thursday, March 04, 2004 9:49 PM Subject: 9i - ASSM

: We are having a debate on building tablespaces with automatic segment
space
: management (ASSM). This is a 9i db on a Solaris box. I'm in favor of
using
: ASSM but the senior dba is a bit hesitant and want to put in manual
mode.
: I've even tried to persuade him with the Oracle documentation but he
insists
: its not mature enough for production.
:
: Is there any white papers or matalink papers that show the pros and
cons
to
: ASSM in 9i? Has anyone had issues with using ASSM? Is there a way of
proving
: ASSM is better than MSSM?
:
: Thanks,
:
: Mark
:

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Received on Fri Mar 05 2004 - 10:35:48 CST