Query a database specific configuration parameter

Question

I have a postgres 9.6 server with > 100 databases on it. When doing a mass-migrate, I use statements like this:

ALTER DATABASE mydatabase SET default_transaction_read_only = false;

Which works great. However, occasionally I get into a state where I'm not sure which databases are read only and which aren't. How do I query this parameter? I know how to query it server-wide:

SHOW default_transaction_read_only;

But not at a database specific level.

Answer 1

These settings are stored in the pg_catalog.pg_db_role_setting system catalog. You can search for the databases that have the above setting like

SELECT datname 
  FROM (SELECT datname, unnest(setconfig) AS setting
          FROM pg_db_role_setting 
          JOIN pg_database AS d ON setdatabase = d.oid) AS t 
 WHERE setting = 'default_transaction_read_only=false';