Just thinking aloud....
High water mark (HWM)is the boundary between ever used and never used space in a segment. Oracle always reads up to the HWM during full table scan, no matter if the space is empty.
Why CBO doesn't know this fact?
It should just be a matter of adding yet another statistic in the arsenal of CBO and should be gathered up during stat gathering job?
Or am I missing something here....
2 comments:
the FTS cost is calculated as
FTS cost = Blocks below HWM / MBRC * MREADTIM / SREADTIM
thus HWM is indirectly in the formula
Thanks for your comment.
In the formula of FTS Cost, there is no mention of *empty* blocks below HWM.
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