Re: Oddity in EXPLAIN for foreign/custom join pushdown plans

> -----Original Message-----
> From: Etsuro Fujita [mailto:fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp]
> Sent: Monday, August 01, 2016 8:26 PM
> To: Ashutosh Bapat
> Cc: Kaigai Kouhei(海外 浩平); pgsql-hackers(at)postgresql(dot)org
> Subject: Re: [HACKERS] Oddity in EXPLAIN for foreign/custom join pushdown plans
>
> On 2016/07/29 13:28, Ashutosh Bapat wrote:
>
> I wrote:
> > Probably something like this:
> >
> > Foreign Processing
> > Remote Operations: ...
> >
> > In the Remote Operations line, the FDW/extension could print
> > any info
> > about remote operations, eg, "Scan/Join + Aggregate".
>
> I wrote:
> > I intentionally chose that word and thought we could leave detailed
> > descriptions about remote operations to the FDW/extension; a broader
> > word like "Processing" seems to work well because we allow various
> > kinds of operations to the remote side, in addition to scans/joins,
> > to be performed in that one Foreign Scan node indicated by "Foreign
> > Processing", such as aggregation, window functions, distinct, order
> > by, row locking, table modification, or combinations of them.
>
> > "Scan" is a better word than "Processing". From plan's perspective it's
> > ultimately a Scan (on the data produced by the foreign server) and not
> > processing.
>
> Exactly, but one thing I'm concerned about is the table modification
> case; the EXPLAIN output would be something like this:
>
> Foreign Scan
> Remote SQL: INSERT INTO remote_table VALUES ...
>
> That would be strange, so I think a more broader word is better. I
> don't think "Foreign Processing" is best. "Foreign Upper" might be much
> better because the corresponding path is created by calling
> GetForeignUpperPaths.
>
Be "Foreign %s", and gives "Insert" label by postgres_fdw; which knows
the ForeignScan node actually insert tuples.
From the standpoint of users, it looks "Foreign Insert".

> Also for a Foreign Scan representing a foreign join, I think "Foreign
> Join" is better than "Foreign Scan". Here is an example:
>
> Foreign Join on foreign_table1, foreign_table2
> Remote SQL: SELECT ... FROM remote_table1 INNER JOIN remote_table2
> WHERE ...
>
> I think "Foreign Join" better indicates that foreign tables listed after
> that (ie, foreign_table1 and foreign_table2 in the example) are joining
> (or component) tables of this join, than "Foreign Scan".
>
Postgres_fdw knows it is remote join. It is quite easy to tell the core
this ForeignScan node is "Join". Also, it knows which tables are involved in.
We can add hint information to control relations name to be printed.

Thanks,
--
NEC Business Creation Division / PG-Strom Project
KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>