What is the function of grouping_planner function in PostgreSQL

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Source code interpretation

Grouping / aggregation and other operations are superimposed on a Relation. The grouping_planner function first generates a new relationship through the query_planner function, and then attached the grouping / aggregation and other operations on this relationship.

/ *-* grouping_planner * Perform planning steps related to grouping, aggregation, etc. * perform the "planning steps" related to grouping / clustering. * grouping / aggregating operations are superimposed on a Relation. * PG first generates a new relationship through the query_planner function, and then attached grouping / aggregating operations on this relationship * * This function adds all required top-level processing to the scan/join * Path (s) produced by query_planner. * * this function also handles all scan / connection paths that need to be processed at the top level (generated by the query_planner function) * * If inheritance_update is true, we're being called from inheritance_planner * and should not include a ModifyTable step in the resulting Path (s). * (inheritance_planner will create a single ModifyTable node covering all the * target tables.) * * if the flag inheritance_update is true, the caller of this function is inheritance_planner, and the ModifyTable step should not be included in the result path (inheritance_planner creates a separate ModifyTable node that covers all target tables). * * tuple_fraction is the fraction of tuples we expect will be retrieved. * tuple_fraction is interpreted as follows: * 0: expect all tuples to be retrieved (normal case) * 0

< tuple_fraction < 1: expect the given fraction of tuples available * from the plan to be retrieved * tuple_fraction >