View open connections to a PostgreSQL 9.2+ database. Quite useful when you're seeing ActiveRecord::ConnectionTimeoutError on Heroku.

postgres_open_connections.sql

-- On Heroku:
-- $ heroku pg:psql

-- An explaination of the columns on the pg_stat_activity table:
--   http://www.postgresql.org/docs/9.2/static/monitoring-stats.html#PG-STAT-ACTIVITY-VIEW
select
  pid, application_name, query, waiting, state, state_change
from pg_stat_activity
where usename = current_user
order by state_change desc;

Also this:

https://github.com/heroku/heroku-pg-extras