Re: Status of FDW pushdowns

On Thu, Nov 28, 2013 at 01:29:46AM +0530, Atri Sharma wrote:
> On Thu, Nov 28, 2013 at 12:54 AM, David Fetter <david(at)fetter(dot)org> wrote:
> > On Wed, Nov 27, 2013 at 10:29:34AM -0300, Alvaro Herrera wrote:
> >> Shigeru Hanada escribió:
> >>
> >> > SQL/MED standard doesn't say much about PASS THROUGH mode, especially
> >> > about interaction between client. Besides it, I think it would be
> >> > nice to allow arbitrary FDW as backend of dblink interface like this:
> >> >
> >> > postgres=> SELECT dblink_connect('con1', 'server name of an FDW');
> >> > postgres=> SELECT * FROM dblink('con1', 'some query written in remote
> >> > syntax') as t(/* record type definition */...);
> >> >
> >> > This provides a way to execute query without defining foreign table.
> >>
> >> Seems to me that if you want to read remote tables without creating a
> >> foreign table, you could define them locally using something like the
> >> WITH syntax and then use them normally in the rest of the query.
> >
> > WITH, or SRF, or whatever, the point is that we need to be able to
> > specify what we're sending--probably single opaque strings delimited
> > just as we do other strings--and what we might get back--errors only,
> > rows, [sets of] refcursors are the ones I can think of offhand.
>
> +1
>
> The input-output formats need to be defined clearly.
>
> How about sending parse trees? Is it even possible?

I don't see why parse trees wouldn't be something that could
eventually be sent to other PostgreSQL servers, but I see that whole
discussion as orthogonal to this one.

My point here is that there needs to be an "escape to native" system
available in SQL so people can communicate directly with the remote
systems in the systems' own languages. It's a little bit analogous to
making assembler available from C, or C from HLLs.

> > What we can't do is assume that our parser needs to, or even could, in
> > principle, understand these things in more detail than that.
>
> Agreed.
>
> I wonder if its possible to give this task to the FDW implementing
> authority instead, and get FDW to translate to the required format.

I don't know that the FDW would necessarily need to get involved
except in the sense of "full recognition before processing."
http://langsec.org/occupy/

Cheers,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter
Skype: davidfetter XMPP: david(dot)fetter(at)gmail(dot)com
iCal: webcal://www.tripit.com/feed/ical/people/david74/tripit.ics

Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate