Tagging PostgreSQL database Is it possible to "tag" a PostgreSQL database with meta-data? 

Here is my intended use case: I have a database that goes through several workflow steps, and it would be nice to record somewhere around a database that a step has been taken. Of course there could be a table inside the database for recording this, but I am not supposed to change the schema for the task at hand. 

Could/should e.g. custom options (e.g. ALTER DATABASE db SET a.b = 'c') serve such a purpose?
As a_horse commented, a COMMENT ON DATABASE db IS 'foo'; would be a simple option. 

set_config() settings are for the duration of the transaction or session only. If you need to persist information beyond the current session, that won't do.

For more structured bookkeeping, maybe including a timestamp etc, consider a bookkeeping table in another database in the same db cluster - without altering the db in question at all. (Maybe in addition to a comment on the main db indicating the current status.) Sample psql session:

CREATE DATABASE db_meta;
\c db_meta
CREATE TABLE db_status_log (
  log_id serial PRIMARY KEY
, log_ts timestamptz NOT NULL DEFAULT now()
, status text
);


Etc.

\c db_meta is the psql meta-command to connect to a db.