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

> 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..140120.31rows=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..734.00rows=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..734.00rows=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)

Thanks,
--
NEC OSS Promotion Center / PG-Strom Project
KaiGai Kohei <kaigai@ak.jp.nec.com>


> -----Original Message-----
> From: Robert Haas [mailto:robertmhaas@gmail.com]
> Sent: Thursday, January 15, 2015 2:07 AM
> To: Kaigai Kouhei(海外 浩平)
> Cc: Tom Lane; pgsql-hackers@postgreSQL.org; Shigeru Hanada
> Subject: ##freemail## Re: Custom/Foreign-Join-APIs (Re: [HACKERS] [v9.5]
> Custom Plan API)
> 
> 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?
> 
> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL
> Company