2012/8/28 David Fetter <da...@fetter.org>: > On Tue, Aug 28, 2012 at 05:18:34PM +0200, Kohei KaiGai wrote: >> 2012/8/28 David Fetter <da...@fetter.org>: >> > On Tue, Aug 28, 2012 at 10:58:25AM -0400, Tom Lane wrote: >> >> Kohei KaiGai <kai...@kaigai.gr.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. > One major problem is how to carry the generated identifiers on run-time, even though we have no slot except for system and regular columns defined in TupleDesc of the target foreign tables. It may need a feature to expand TupleDesc on demand.
Of course, I don't deny the benefit of trigger support on foreign-tables. Both writable-feature and trigger-support can be supported simultaneously. Thanks, -- KaiGai Kohei <kai...@kaigai.gr.jp> -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers