While working on bug #19412 [1], I noticed $subject. For each child qual translated from a parent rel's qual, apply_child_basequals calls eval_const_expressions to simplify it, and then calls restriction_is_always_false and restriction_is_always_true immediately afterward to reduce NullTest expressions. Since the planner performs NullTest deduction during constant folding, I think the call to restriction_is_always_false and restriction_is_always_true is now redundant and wastes CPU cycles.
Attached is a patch to remove them. [1] https://postgr.es/m/[email protected] - Richard
v1-0001-Remove-redundant-restriction-checks-in-apply_chil.patch
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