On 10/25/24 16:26, Ba Jinsheng wrote:
 >So, I wonder if you could analyse the path-choosing logic, determine the
costs of competing paths, and explain why NestLoop wasn't chosen.

To be honest, it is a bit challenging for me.
I guess the better query plan is not considered when comparing the cost of paths?
I personally print all the paths (adding an elog message inside the code) and their costs for specific JOIN. Some paths are filtered on earlier stages and not even have a leg in pathlist. Basically, Postgres already has some extended logging for the optimiser paths - use -DOPTIMIZER_DEBUG compilation flag.

--
regards, Andrei Lepikhov



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