From: | David Fetter <david(at)fetter(dot)org> |
---|---|
To: | Kohei KaiGai <kaigai(at)kaigai(dot)gr(dot)jp> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Shigeru HANADA <shigeru(dot)hanada(at)gmail(dot)com>, PgHacker <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [v9.3] writable foreign tables |
Date: | 2012-08-28 15:25:14 |
Message-ID: | 20120828152514.GD17812@fetter.org |
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Thread: | |
Lists: | pgsql-hackers |
On Tue, Aug 28, 2012 at 05:18:34PM +0200, Kohei KaiGai wrote:
> 2012/8/28 David Fetter <david(at)fetter(dot)org>:
> > On Tue, Aug 28, 2012 at 10:58:25AM -0400, Tom Lane wrote:
> >> Kohei KaiGai <kaigai(at)kaigai(dot)gr(dot)jp> writes:
> >> > It seems to me TargetEntry of the parse tree can inform us
> >> > which column should be modified on UPDATE or INSERT. If it has
> >> > just a Var element that reference original table as-is, it
> >> > means here is no change.
> >>
> >> Only if you're not going to support BEFORE triggers modifying the
> >> row...
> >
> > +1 for supporting these.
> >
> > Speaking of triggers on foreign tables, what's needed to support
> > them independent of support at the FDW level for writing on
> > foreign tables, or does that even make sense?
> >
> I agree with trigger support on foreign tables is definitely useful
> feature, even though it does not have capability to replace the
> writable foreign table functionality.
With utmost respect, trigger support does make it possible to write to
foreign tables using a whole-row comparison with the effect that all
whole-row matches would be affected. This is how DBI-Link does it
currently.
> In case when foreign-table definition does not contain a column
> mapped with primary-key column in remote-side, the trigger function
> cannot determine which row should be updated / deleted. It is a
> situation that FDW driver should track a particular remote-row using
> its identifier.
Generated identifiers and whole-row matching are two ways to approach
this. There are likely others, especially in cases where people have
special knowledge of the remote source.
Cheers,
David.
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