django-pglocks provides a useful context manager to manage PostgreSQL advisory
locks. It requires Django (tested with 1.5), PostgreSQL, and (probably) psycopg2.
Advisory locks are application-level locks that are acquired and released purely
by the client of the database; PostgreSQL never acquires them on its own. They
are very useful as a way of signalling to other sessions that a higher-level
resource than a single row is in use, without having to lock an entire table or
some other structure.
It's entirely up to the application to correctly acquire the right lock.
Advisory locks are either session locks or transaction locks. A session lock is
held until the database session disconnects (or is reset); a transaction lock is
held until the transaction terminates.
Currently, the context manager only creates session locks, as the behavior of a
lock persisting after the context body has been exited is surprising, and
there's no way of releasing a transaction-scope advisory lock except to exit