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feat: Support limit operations #58
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yliang412
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Feb 12, 2024
| @@ -107,6 +107,11 @@ impl CostModel<OptRelNodeTyp> for OptCostModel { | |||
| Self::cost(row_cnt, 0.0, row_cnt) | |||
| } | |||
| OptRelNodeTyp::PhysicalEmptyRelation => Self::cost(0.5, 0.01, 0.0), | |||
| OptRelNodeTyp::PhysicalLimit => { | |||
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Just wondering how is this determined?
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I don't fully understand the cost system in play here just yet, but there are a few things to notice:
-The row_cnt is from the child tuple
- I multiply by selectivity as a very rough estimate for what the cost might be
- usually LIMIT clauses are quite selective, so that is my sketchy reasoning for 0.001. Also, it is the same selectivity as FILTER.
- the computation cost for this one I just set to
row_cnt. No reasoning really. Looking again at other examples, I think that should probably be compute_cost from the child, so I will change it.
There is probably a cleverer way to do this by actually reading LIMIT, but I think it might be best to leave that for a real cost model.
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