environment variables can now be used to set options: if an environment variable is set using `SAT_PUBSUB_[OPTION NAME]` it will be used if not specified directly in command line. Options are retrieved in this order of priority: - command line (highest priority) - environment variable - option set in `sat.conf` For database options, following PostgreSQL aliases can also be used: PGUSER, PGDATABASE, PGPASSWORD, PGHOST, PGPORT.

create table callbacks (
    service text not null,
    node text not null,
    uri text not null,
    PRIMARY KEY (service, node, uri)
);