Re: Wrong optimizer estimate ?
- From: Kellyn Pedersen <kjped1313@xxxxxxxxx>
- To: Michael.Seiwert@xxxxxx
- Date: Mon, 8 Nov 2010 18:24:02 -0800 (PST)
And to append to Jared's email... I also ask my developers to look at the
column statistics data collected in dba_tab_columns. It's higher level, but
very helpful in letting them know what columns have statistics, how many
distinct values, if histograms have been collected, etc...
Kellyn Pedersen
Sr. Database Administrator
http://www.linkedin.com/in/kellynpedersen
www.dbakevlar.com
________________________________
From: Jared Still <jkstill@xxxxxxxxx>
To: Michael.Seiwert@xxxxxx
Cc: oracle-l@xxxxxxxxxxxxx
Sent: Mon, November 8, 2010 3:51:08 PM
Subject: Re: Wrong optimizer estimate ?
On Sun, Nov 7, 2010 at 1:53 AM, Michael Seiwert <Michael.Seiwert@xxxxxx> wrote:
Hi all,
>
>while doing performance tests of some new queries in our application I noticed
>one query where the estimated rows differ much from the actual rows in the
>execution plan (Line 7 in the attached execution plan).
For a start, you may want to investigate DBA_TABLES and DBA_INDEXES
to determine when statistics were gathered.
If the data has grown, the actual # of rows could easily be greater than
what is stored in statistics.
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist
Oracle Blog: http://jkstill.blogspot.com
Home Page: http://jaredstill.com
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