This patch adds the core-system infrastructure needed to support updates
on foreign tables, and extends contrib/postgres_fdw to allow updates
against remote Postgres servers. There's still a great deal of room for
improvement in optimization of remote updates, but at least there's basic
functionality there now.
KaiGai Kohei, reviewed by Alexander Korotkov and Laurenz Albe, and rather
heavily revised by Tom Lane.
Include eval costs of local conditions in remote-estimate mode, and don't
assume the remote eval cost is zero in local-estimate mode. (The best
we can do with that at the moment is to assume a seqscan, which may well
be wildly pessimistic ... but zero won't do at all.)
To get a reasonable local estimate, we need to know the relpages count
for the remote rel, so improve the ANALYZE code to fetch that rather
than just setting the foreign table's relpages field to zero.
There's still a lot of room for improvement, but it basically works,
and we need this to be present before we can do anything much with the
writable-foreign-tables patch. So let's commit it and get on with testing.
Shigeru Hanada, reviewed by KaiGai Kohei and Tom Lane
Tom Lane