Re: patch: SQL/MED(FDW) DDL

On Fri, Oct 01, 2010 at 10:54:47AM -0400, Tom Lane wrote:
> David Fetter <david(at)fetter(dot)org> writes:
> > On Thu, Sep 30, 2010 at 10:29:56PM -0400, Robert Haas wrote:
> >> Yeah, that might be better. Is it reasonable to assume we always
> >> want to push down as much as possible, or do we need to think about
> >> local work vs. remote work trade-offs?
>
> > In cases where the foreign side is not super reliable for correctness,
> > I'd say there's a good case for not trusting it. Some of the Oracle
> > properties are like this. I suppose we might want to make "trust the
> > other side to handle pushed quals" optional somehow, but I'm not
> > exactly sure how.
>
> ISTM that such decisions would be embedded in the FDW

s/embedded in/& and overrides communicable to/

In an upcoming version of DBI-Link, I've got some code that allows
transformations between types on PostgreSQL and foreign sources, for
now when they have the same name. The transformations are implemented
on the PostgreSQL side, although I a plan for (optionally) pushing
them to the foreign side.

There's an input transformation and an output transformation, both of
which default to the identity transformation, i.e. "do nothing."
These transformations are over-ridable at the following levels, with
the finer-grained one taking precedence over the coarser should there
be more than one user-supplied transformation:

- database type (Oracle, CSV, etc.)
- catalog (Database cluster in PostgreSQL parlance, i.e. everything
served on a single host/port combination. DB2 actually implements
this under that name.)
- database
- schema
- table
- column

> --- it's unlikely that the FDW for Oracle would look even a little
> bit like the one for Postgres anyway, so contemplating ways to
> parameterize them seems a rather useless exercise.

See above for a parameterization :)

Cheers,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
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