On Thu, Sep 30, 2010 at 10:29:56PM -0400, Robert Haas wrote: > On Sep 29, 2010, at 10:09 AM, Alvaro Herrera <alvhe...@commandprompt.com> > wrote: > > Excerpts from Robert Haas's message of mar sep 28 10:26:54 -0400 2010: > > > >> Then: > >> > >> - Begin a sequential scan with the following set of quals. > >> - Begin an index scan using the index called X with the following set of > >> quals. > >> - Fetch next tuple. > >> - End scan. > > > > I'm not sure that it's a good idea to embed into the FDW API the > > set of operations known to the executor. For example your > > proposal fails to consider bitmap scans. Seems simpler and more > > general to hand the quals over saying "I need to scan this > > relation with these quals", and have it return an opaque iterable > > object; the remote executor would be in charge of determining > > their usage for indexscans; or even for filtering tuples with > > quals that cannot be part of the index condition. > > 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. > > There doesn't to be much point in knowing the names of remote > > indexes either (if it came to referencing them, better use OIDs) > > Well, you can't assume the remote side is PG. Very definitely not. The main point of the feature is that it allows for *heterogeneous* data stores. Of course this doesn't prevent PostgreSQL from optimizing aggressively using secret knowledge should the "foreign" side happen to be PostgreSQL. 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
