On Wed, Mar 26, 2008 at 02:26:41PM -0700, Neil Conway wrote: > On Wed, 2008-03-26 at 14:38 -0400, Andrew Dunstan wrote: > > I'm still waiting to see an example of where you say this patch is > > even marginally useful. > > It's not hard to think of one: > > SELECT * FROM remote_table() WHERE x = 5;
In DBI-Link's case, remote_table() may not have all the nice features a Postgres data store would. It might or might not have indexes, for example, and the best hints it could get might well be those predicates supplied by DBI-Link. > Applying the predicate on the remote database (pushing the predicate > below the function scan) is an elementary optimization, and in many > cases would be enormously more efficient than materializing the > entire remote table at the local site and then applying the qual > there. > > Certainly I agree with Tom that proper SQL/MED support requires > significant support from both the executor and the optimizer. > This is just a quick hack to take advantage of the existing > predicate pushdown logic -- I just thought it was a cute trick, not > something I'd suggest we include in mainline sources. I disagree that it's "just" a cute trick. I've managed to get dblink to use it transparently with dblink :) Cheers, David. -- David Fetter <[EMAIL PROTECTED]> http://fetter.org/ Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter Skype: davidfetter XMPP: [EMAIL PROTECTED] Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
