Re: Join push-down support for foreign tables

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.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company