On Wed, Dec 22, 2010 at 03:00:16PM +0000, Simon Riggs wrote: > On Wed, 2010-12-22 at 09:03 -0500, Andrew Dunstan wrote: > > > Answering a few of your questions > > Many thanks. > > > > 7. Why does ANALYZE skip foreign tables? Surely its really > > > important we know things about a foreign table, otherwise we are > > > going to optimize things very badly. > > > > Quite apart from other reasons, such as possible ephemerality of > > the data, the difficulty of taking a reasonable random sample from > > an arbitrary foreign data source seems substantial, and we surely > > don't want ANALYSE to have to run a full sequential scan of a > > foreign data source. > > I think we need something that estimates the size of a table, at > least, otherwise queries will be completely un-optimised.
The estimated size for a lot of things--streams of data, for example--is infinity. I suppose that's a good default for some cases. > > > 10. Can a foreign table be referenced by a FK? > > > > I don't see how it can be. There would be no unique index to use. > > That answers another question also. There might be some cases where we can say an expression on a set of columns is unique, but not in the general case. In the general case, we can't even guarantee 1NF. > Still many unanswered. Will try these later today :) Cheers, David. -- David Fetter <da...@fetter.org> http://fetter.org/ Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter Skype: davidfetter XMPP: david.fet...@gmail.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 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
