Re: Join push-down support for foreign tables

2014-12-16 1:22 GMT+09:00 Robert Haas <robertmhaas@gmail.com>:
> On Mon, Dec 15, 2014 at 3:40 AM, Shigeru Hanada
> <shigeru.hanada@gmail.com> wrote:
>> I'm working on $SUBJECT and would like to get comments about the
>> design.  Attached patch is for the design below.
>
> I'm glad you are working on this.
>
>> 1. Join source relations
>> As described above, postgres_fdw (and most of SQL-based FDWs) needs to
>> check that 1) all foreign tables in the join belong to a server, and
>> 2) all foreign tables have same checkAsUser.
>> In addition to that, I add extra limitation that both inner/outer
>> should be plain foreign tables, not a result of foreign join.  This
>> limiation makes SQL generator simple.  Fundamentally it's possible to
>> join even join relations, so N-way join is listed as enhancement item
>> below.
>
> It seems pretty important to me that we have a way to push the entire
> join nest down.  Being able to push down a 2-way join but not more
> seems like quite a severe limitation.

Hmm, I agree to support N-way join is very useful.  Postgres-XC's SQL
generator seems to give us a hint for such case, I'll check it out
again.

-- 
Shigeru HANADA