2015-05-12 10:24 GMT+09:00 Kouhei Kaigai <kaigai@ak.jp.nec.com>:
> option-2)
> Tom's suggestion. Add a new list field of Path nodes on CustomPath,
> then create_customscan_plan() will call static create_plan_recurse()
> function to construct child plan nodes.
> Probably, the attached patch will be an image of this enhancement,
> but not tested yet, of course. Once we adopt this approach, I'll
> adjust my PG-Strom code towards the new interface within 2 weeks
> and report problems if any.
+1. This design achieves the functionality required for custom join
by Kaigai-san's use case, instantiating sub-plans of CustomScan plan
recursively, without exposing create_plan_recurse. CSP can use the
index number to distinguish information, like FDWs do with
fdw_private.
IMO it isn't necessary to apply the change onto
ForeignPath/ForeignScan. FDW would have a way to keep-and-use sub
paths as private information. In fact, I wrote postgres_fdw to use
create_plan_recurse to generate SQL statements of inner/outer
relations to be joined, but as of now SQL construction for join
push-down is accomplished by calling private function deparseSelectSql
recursively at the top of a join tree.
Some FDW might hope to use sub-plan generation, but we don't have any
concrete use case as of now.
--
Shigeru HANADA