RE: Cost of hash join
- From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- To: "Christo Kutrovsky" <kutrovsky.oracle@xxxxxxxxx>
- Date: Mon, 13 Jun 2005 10:52:13 +0200
Hi Christo
>Where did you get the number of slots available and needed from?
>
>"In the second case we need about 116 slots but only 17 are available"
My apologies, there's an error here... What I meant is "166 times the available
memory for the slots".
>Which trace told you that ? I cant seem to find tehse numbers
>(especially 116) in the trace outputs you gave.
My understanding/guess is that the CBO compares the "result set size" ("bytes"
in execution plan) with "memory for slots".
In the first case 400000 is smaller than 983040 --> therefore low cost.
In the second case 80400000 is much greater than 696320 (about 116 times) -->
therefore "high" cost.
HTH
Chris
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