[JoinReorder] Implement a better join reorder algorithm #6226
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Proposed changes
The current JoinReorder algorithm mainly sorts according to the star model,
and only considers the query association relationship between the table and the table.
The problems are following:
and the real query optimization ability is weak.
The new JoinReorder algorithm mainly introduces a new sorting algorithm for Join
The new ranking algorithm introduces the cost evaluation model to Doris.
The sorting algorithm is mainly based on the following three principles:
PlanNode's cost model evaluation mainly relies on two values: cardinality and selectivity.
cardinality: cardinality, can also be simply understood as the number of rows.
selectivity: selectivity, a value between 0 and 1. Predicate generally has selectivity.
The cost model generally calculates the final cardinality of a PlanNode based on the pre-calculated
cardinality of PlanNode and the selectivity of the predicate to which it belongs.
Currently, you can configure "enable_cost_based_join_reorder" to control the opening and closing of JoinReorder.
When the configuration is turned on, the new sorting algorithm will take effect, when it is turned off,
the old sorting algorithm will take effect, and it is turned off by default.
The new sorting algorithm currently has no cost base evaluation for external tables (odbc, es)
and set calculations (intersect, except). When using these queries, it is not recommended to enable cost base join reoder.
When using these queries, it is not recommended to enable cost base join reoder.
At the code architecture level:
and cost evaluation have been completed before the sorting algorithm occurs.
Change-Id: I6a89b20d70ff1d49909900f39337fa31cc8efd1e
Types of changes
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