Thanks for the detailed instructions, Laurenz!
"The foreign server encapsulates the connection string to access a
remote
PostgreSQL database. Define one per remote database you want to
access."
Where do I define "one per remote database"?.....in pg_hba.conf?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Susan E Hurst
Principal Consultant
Brookhurst Data LLC
Email: susan.hurst@xxxxxxxxxxxxxxxxxx
Mobile: 314-486-3261
On 2020-11-09 11:12, Laurenz Albe wrote:
On Sun, 2020-11-08 at 13:09 -0600, Susan Hurst wrote:
The first pass thru https://www.postgresql.org/docs/12/fdwhandler.html
does not tell me what I think I need to know, but I will digest this
more thoroughly. Maybe I need to understand more of the lingo re:
foreign data wrappers. I do understand that all fdw names must be
unique
within a database so if I want to connect to more than one foreign db,
I
need a different name for each connection. I cannot name each fdw
postgres_fdw. I would like to name the fdws something like:
dbname_to_foreigndbname.
For example, here are 2 possible fdws:
create foreign data wrapper stp_to_geo;
create foreign data wrapper stp_to_metrics;
That syntax creates the fdw and I can create user mappings but I
cannot
import any foreign schemas into my database. The error message says
that
there is no handler for the fdw. That's where I'm stuck.
BTW, I did try using postgres_fdw as a handler...
create foreign data wrapper stp_to_geo handler postgres_fdw;
...but then I got these errors:
ERROR: function postgres_fdw() does not exist
ERROR: foreign-data wrapper "stp_to_geo" does not exist
Looks like I need to study a bit more.
This is how you would create a new foreign data wrapper object for
PostgreSQL:
CREATE FOREIGN DATA WRAPPER myfdw
HANDLER public.postgres_fdw_handler
VALIDATOR public.postgres_fdw_validator;
This assumes that you installed the extension "postgres_fdw" in schema
"public".
But you normally don't have to create a new foreign data wrapper: the
one named
"postgres_fdw" that is created by the extension is good enough.
The only reason would be to have a foreign data wrapper with
non-default options,
but since there are no options for "postgres_fdw", that is moot.
So don't do that.
The hierarchy of objects is as follows:
- The foreign data wrapper encapsulates the code required to access the
foreign
data source. You need only one per database; no need to create a new
one.
- The foreign server encapsulates the connection string to access a
remote
PostgreSQL database. Define one per remote database you want to
access.
- The user mapping encapsulates the credentials for a user to access a
foreign server.
Create one per user and foreign server (or a single one for PUBLIC =
everybody).
- The foreign table describes how a remote table is mapped locally.
Define one per table that interests you.
Yours,
Laurenz Albe
