Re: Custom/Foreign-Join-APIs (Re: [v9.5] Custom Plan API)

Tom,

I briefly checked your updates.
Even though it is not described in the commit-log, I noticed a
problematic change.

This commit reverts create_plan_recurse() as static function. It means extension
cannot have child node, even if it wants to add a custom-join logic.
Please assume a simple case below: SELECT * FROM t0, t1 WHERE t0.a = t1.x;

An extension adds a custom join path, then its PlanCustomPath method will be
called back to create a plan node once it gets chosen by planner.
The role of PlanCustomPath is to construct a plan-node of itself, and plan-nodes
of the source relations also.
If create_plan_recurse() is static, we have no way to initialize
plan-node for t0
and t1 scan even if join-logic itself is powerful than built-in ones.

It was already discussed in the upthread, and people's consensus.
Please revert create_plan_recurse() as like initial commit.

Also, regarding of the *_scan_tlist,

> I don't have time to pursue this idea right now, but I think it would be
> a good change to squeeze into 9.5, just so that we could have some test
> coverage on those parts of this patch.
>
Do you want just a test purpose module and regression test cases?

Thanks,
-- 
KaiGai Kohei <kaigai@kaigai.gr.jp>