Using postgres_fdw to connect from one read replica to another

Question

I have two postgres database servers in AWS, A and B. These databases have different tables. Both databases also have their own read replica.

My goal is a simple solution for doing cross database joins from A replica to B replica. Querying from master is not an option, as this feature is meant for the analyst on my team, not for an application.

I set up postgres_fdw on A's master following the instructions by doing CREATE SERVER, CREATE USER MAPPING, and CREATE FOREIGN TABLEs, and I was able to easily query from A master to B replica. However, these server and foreign table definitions did NOT replicate to A replica. I am unable to run these create commands on the replica as it is read-only.

Is it possible to use postgres_fdw from A replica to B replica? If not, is there another solution for this problem?

Answer 1

You can create replicas using logical decoding. Check pglogical https://github.com/2ndQuadrant/pglogical

When creating replica using logical decoding it's not read-only.Might help in your case.

Answer 2

The general approach here would be creating extension, server, user mapping and foreign tables on master.

Then query all those on any slave...