How to share a table between multiple Postgresql databases

Question

My web app has multiple deployments -- each is a unique site with a unique URL.
Each deployment has different data, UI, etc. but a very similar Postgresql database structure

Answer 1

Yes, schemas are the solution. Use a single PostgreSQL cluster, with a single database.

Create a group for all of app users:

CREATE ROLE app;

Create global "app" schema, where all global shared applications tables will live.

CREATE SCHEMA AUTHORIZATION app;
CREATE TABLE app.objects ( objectid int PRIMARY KEY );
ALTER TABLE app.objects OWNER TO app;

Create separate user (with no superuser rights) for each of deployments:

CREATE USER app01 IN ROLE app;
CREATE USER app02 IN ROLE app;

Optionally, instead of IN ROLE app, you can grant explicit rights for these users on selected app objects:

GRANT USAGE ON SCHEMA app TO app01;
GRANT SELECT on app.objects TO app01;

Create private schemas, where deployment-dependent tables will live:

CREATE SCHEMA AUTHORIZATION app01; 
CREATE SCHEMA AUTHORIZATION app02;

Now you have a private schema for every application deployed; but at the same time you have shared access to global data.

What's nice, is that application does not have to be schema-aware. SELECT * FROM froobles will by default resolve to SELECT * FROM app01.froobles, if you are connected as app01 user. You do not have to specify schema name.

As an extra measure, you can use table inheritance to extend global objects on per-deployment basis:

CREATE TABLE app01.objects (
  localattr1 int,
  localattr2 text
)
INHERITS ( app.objects );