Re: Moving SS_finalize_plan processing to the end of planning - Mailing list pgsql-hackers

I've started to work on path-ification of the upper planner (finally),
and since that's going to be a large patch in any case, I've been looking
for pieces that could be bitten off and done separately.  One such piece
is the fact that SS_finalize_plan (computation of extParams/allParams)
currently gets run at the end of subquery_planner; as long as that's true,
we cannot have subquery_planner returning paths rather than concrete
plans.  The attached patch moves that processing to occur just before
set_plan_references is run.

Basically what this patch does is to divide what had been done in
SS_finalize_plan into three steps:

* SS_identify_outer_params determines which outer-query-level Params will
be available for the current query level to use, and saves that aside in
a new PlannerInfo field root->outer_params.  This processing turns out
to be the only reason that SS_finalize_plan had to be called in
subquery_planner: we have to capture this data before exiting
subquery_planner because the upper levels' plan_params lists may change
as they plan other subplans.

* SS_attach_initplans does the work of attaching initplans to the parent
plan node and adjusting the parent's cost estimate accordingly.

* SS_finalize_plan now *only* does extParam/allParam calculation.

I had to change things around a bit in planagg.c (which was already a
hack, and the law of conservation of cruft applies).  Otherwise it's
pretty straightforward and removes some existing hacks.  One notable
point is that there's no longer an assumption within SS_finalize_plan
that initPlans can only appear in the top plan node.

Any objections?