Cost-based decision between ORDER and SORT plans #8316
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asfernandes
reviewed
Nov 13, 2024
src/jrd/optimizer/Optimizer.h
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| const double REDUCE_SELECTIVITY_FACTOR_GREATER = 0.05; | ||
| const double REDUCE_SELECTIVITY_FACTOR_STARTING = 0.01; | ||
| const double REDUCE_SELECTIVITY_FACTOR_OTHER = 0.01; | ||
| constexpr double REDUCE_SELECTIVITY_FACTOR_EQUALITY = 0.001; |
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Should not better be inline constexpr?
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Implement cost calculation for the ORDER vs SORT choice when ordering is required for the query. The visible effects are:
ORDER ... INDEXplan is almost never used, being inferior toSORTin most cases -- maybe except some queries withOPTIMIZE FOR FIRST ROWShint, explicit or implicit (e.g.SELECT FIRST). This is already proven in practice to work better.SORTplan may be preferred toORDERfor the defaultOPTIMIZE FOR ALL ROWSscenario if its estimated as being cheaper.ORDERplan will be used always if a suitable index exists. We have a number of QA tests that are affected by this change.The cost calculation will be adjusted once more statistics will be available to the optimizer (e.g. clustering factor).