Hitoshi Harada <umi.tan...@gmail.com> writes: > On Sat, Oct 29, 2011 at 8:13 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> I have not looked at the code, but ISTM the way that this has to work is >> that you set up a portal for each active scan. Then you can fetch a few >> rows at a time from any one of them.
> Hmm, true. Looking back at the original proposal (neither did I look > at the code,) there seems to be a cursor mode. ISTM it is hard for fdw > to know how the whole plan tree looks, so consequently do we always > cursor regardless of estimated row numbers? I think we have to. Even if we estimate that a given scan will return only a few rows, what happens if we're wrong? We don't want to blow out memory on the local server by retrieving gigabytes in one go. > I haven't had much experiences around cursor myself, but is it as > efficient as non-cursor? No, but if you need max efficiency you shouldn't be using foreign tables in the first place; they're always going to be expensive to access. It's likely that making use of native protocol portals (instead of executing a lot of FETCH commands) would help. But I think we'd be well advised to do the first pass with just the existing libpq facilities, and then measure to see where to improve performance. regards, tom lane -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers