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Message Posted: Wed, 09 Aug 2006 @ 18:12:39 GMT


     
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Subj:   Explanation of Explain Plans
 
From:   Anomy Anom

<-- Anonymously Posted: Tuesday, August 08, 2006 06:14 -->

Is there a good white paper or manual that goes over all the details of explain plans? I've read some things that have bits and pieces but haven't found a detailed version. Recently I have two explain plans for the same that appear to be rather similar. One query takes almost 2 hours to run and runs out of spool space quite a bit. The other version runs in about 8 minutes with little spool space. I know what I did to fix the query (added statistics to a source table), but I am trying to figure out how I could have determined this from the explain plans. This will help me with similar queries in the future.

One example that I read on one of the papers in the archive, is that it matters what order the tables appear for merges (left or right) on the explain. Tips like this are helpful as well.


Thanks



     
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