RE: Cost of hash join

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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