Estimating the cost of a plan
Candidate plans are ranked by cost.
Cost estimation relies on:
- Cost model: Predict the cost of each
operator given:
- The operator's algorithm.
- The size of the inputs.
- Ordering of inputs. (Sorted? On what columns?)
- Include the cost of dealing with temporaries, which may
require I/O.
- Size of operator output:
- Number of rows
- Average row width.
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