Jppd 16 - #98
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We don't normally push down join quals into subqueries, because that would require creating parameterized plans. However, if the plan is already parameterized because it's LATERAL, we might as well push down any additional join quals, that refer the same relations that are already referenced within the subquery. This changes the behavior of the sublevels_up parameters to ReplaceVarsFromTargetList(). The targetlist entries used to replace vars are no longer offset by that amount. I'm not sure what the original thinking on it was, but all the existing callers passed sublevels_up = 0, so I hope this is OK.. XXX: fixes by reshke
Plan subqueries a second time, to create parameterized plans with join quals. XXX: fixes by reshke
Introduce a planner GUC, enable_join_predicate_pushdown (default on), that controls whether join and equivalence-class quals are pushed down into LATERAL subqueries. Plain restriction-qual pushdown is unaffected. This gives an escape hatch to disable the optimization and lets the regression tests compare plans and results with and without it. Extend subselect_pushdown with cases that toggle the GUC, verify that restriction quals are still pushed when it is off, and assert that the result set is identical with the optimization on and off (via a symmetric EXCEPT ALL). Update sysviews expected output for the new setting. XXX: fixes by reshke
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