RE: Optimizing a Simple 'select count(*)'

From: McPeak, Matt <vxsmimmcp_at_subaru.com>
Date: Sun, 9 Mar 2014 22:34:55 +0000
Message-ID: <D7864FA3E7830B428CB2A5A5301B63EE7D2B20A2_at_S7041VA005.soa.soaad.com>

Just throwing this out there...

It wouldn't have anything to do with the fact that the from and to dates are bind variables for which we don't know the values? If the initial values given were broad enough, wouldn't Oracle (rightly) choose a FTS over an index?

Matt

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From: oracle-l-bounce_at_freelists.org [oracle-l-bounce_at_freelists.org] on behalf of Jonathan Lewis [jonathan_at_jlcomp.demon.co.uk] Sent: Sunday, March 09, 2014 11:25 AM
To: oracle-l_at_freelists.org
Subject: RE: Optimizing a Simple 'select count(*)'

Even without seeing the code, but assuming there is an index that includes the required data column referenced in the predicate, it does seem a little odd that Oracle has chosen a full tablescan rather than (worst case) an index fast full scan.

The only obvious reason I can think of for this choice is that either the index has grown to a much larger size than it should be, or the only available index includes so many of the table columns that it actually HAS to be larger than the table.

select blocks from user_tables where table_name = ... select leaf_blocks from user_indexes where index_name = ...

Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
_at_jloracle

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From: oracle-l-bounce_at_freelists.org [oracle-l-bounce_at_freelists.org] on behalf of Jared Still [jkstill_at_gmail.com] Sent: 09 March 2014 13:14
To: fmhabash_at_gmail.com
Cc: oracle-l_at_freelists.org
Subject: Re: Optimizing a Simple 'select count(*)'

On Wed, Mar 5, 2014 at 11:56 AM, Fred Habash <fmhabash_at_gmail.com<mailto:fmhabash_at_gmail.com>> wrote: So, why should we live with such costly resource consumptions for such a simple query?

We don't know enough about the tables and/or indexes.

If you include complete code for a reproducible test case, you will likely get more response.

Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist Sr Oracle DBA at Pythian
Pythian Blog http://www.pythian.com/blog/author/still/ Oracle Blog: http://jkstill.blogspot.com Home Page: http://jaredstill.com

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Received on Sun Mar 09 2014 - 23:34:55 CET