A test intended to provoke an error on the remote side was coded in such
a way that multiple rows should be updated, so the output would vary
depending on which one was processed first. Per buildfarm.
For datatypes whose output formatting depends on one or more GUC settings,
we have to worry about whether the other server will interpret the value
the same way it was meant. pg_dump has been aware of this hazard for a
long time, but postgres_fdw needs to deal with it too. To fix data
retrieval from the remote server, set the necessary remote GUC settings at
connection startup. (We were already assuming that settings made then
would persist throughout the remote session.) To fix data transmission to
the remote server, temporarily force the relevant GUCs to the right values
when we're about to convert any data values to text for transmission.
This is all pretty grotty, and not very cheap either. It's tempting to
think of defining one uber-GUC that would override any settings that might
render printed data values unportable. But of course, older remote servers
wouldn't know any such thing and would still need this logic.
While at it, revert commit f7951eef89, since
this provides a real fix. (The timestamptz given in the error message
returned from the "remote" server will now reliably be shown in UTC.)
We probably need to tell the remote server to use specific timezone and
datestyle settings, and maybe other things. But for now let's just hack
the postgres_fdw regression test to not provoke failures when run in
non-EST5EDT environments. Per buildfarm.
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.
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