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

> On Fri, Jan 9, 2015 at 10:51 AM, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
> > When custom-scan node replaced a join-plan, it shall have at least two
> > child plan-nodes. The callback handler of PlanCustomPath needs to be
> > able to call create_plan_recurse() to transform the underlying
> > path-nodes to plan-nodes, because this custom-scan node may take other
> > built-in scan or sub-join nodes as its inner/outer input.
> > In case of FDW, it shall kick any underlying scan relations to remote
> > side, thus we may not expect ForeignScan has underlying plans...
>
> Do you have an example of this?
>
Yes, even though full code set is too large for patch submission...

https://github.com/pg-strom/devel/blob/master/src/gpuhashjoin.c#L1880

This create_gpuhashjoin_plan() is PlanCustomPath callback of GpuHashJoin.
It takes GpuHashJoinPath inherited from CustomPath that has multiple
underlying scan/join paths.
Once it is called back from the backend, it also calls create_plan_recurse()
to make inner/outer plan nodes according to the paths.

In the result, we can see the following query execution plan that CustomScan
takes underlying scan plans.

postgres=# EXPLAIN SELECT * FROM t0 NATURAL JOIN t1 NATURAL JOIN t2;
                                    QUERY PLAN
----------------------------------------------------------------------------------
 Custom Scan (GpuHashJoin)  (cost=2968.00..140120.31 rows=3970922 width=143)
   Hash clause 1: (aid = aid)
   Hash clause 2: (bid = bid)
   Bulkload: On
   ->  Custom Scan (GpuScan) on t0  (cost=500.00..57643.00 rows=4000009 width=77)
   ->  Custom Scan (MultiHash)  (cost=734.00..734.00 rows=40000 width=37)
         hash keys: aid
         nBatches: 1  Buckets: 46000  Memory Usage: 99.99%
         ->  Seq Scan on t1  (cost=0.00..734.00 rows=40000 width=37)
         ->  Custom Scan (MultiHash)  (cost=734.00..734.00 rows=40000 width=37)
               hash keys: bid
               nBatches: 1  Buckets: 46000  Memory Usage: 49.99%
               ->  Seq Scan on t2  (cost=0.00..734.00 rows=40000 width=37)
(13 rows)