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Message Posted: Fri, 15 May 2009 @ 09:49:02 GMT

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The explain plan is produced by the optimiser on the basis of the statistics that have been gathered. On the basis of those statistics, the optimiser develops several plans and then offers you the lowest cost plan. e.g. it will redistribute the smallest tables and answersets.

The Explain will include the words "with low confidence" if statistics have not been gathered for the join you require e.g. if the PI is Col1&2 and stats have only been collected on those but you are joining on col17 then the optimiser knows the maximum number of records in that table but not the number of distinct values in Col17. If you have a feel for the number of rows you expect then you can simply accept a plan which quotes a high cost with low confidence.

Or, try with a subset of the data - e.g. insert a parameter to limit the rows for the largest table which is to be redistributed.

Kenneth Hansen

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