RE: ** histograms

  • From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
  • To: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
  • Date: Mon, 20 Nov 2006 12:35:44 -0700

That is a very nice and accurate analysis. Allowing the CBO to make a more accurate cardinality estimates is what histograms are all about. That may have the consequence that the CBO chooses an index access path if a suitable index is available, but that is by no means the only possible consequence. Seeing histograms only in connection with an index is seeing it too narrowly.

PS. the testcase is in the paper 'Histograms - Myths and Facts" on my website.

At 11:41 AM 11/20/2006, Allen, Brandon wrote:
I'm curious to see the example too. My guess is that the histograms made a difference in the CBO's cardinality estimate, which in turn caused it to choose a different join method or join order.


Wolfgang Breitling
Centrex Consulting Corporation
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