[Fixed]-Real-Time Database Messaging

Currently we’ve rolled our own solution for this entire thing using
overloaded save() methods on the Django table models.

Instead of working on the app level you might want to work on the lower, database level.

Add a PostgreSQL trigger after row insertion, and use pg_notify to notify external apps of the change.

Then in NodeJS:

var PGPubsub = require('pg-pubsub');

var pubsubInstance = new PGPubsub('postgres://username@localhost/tablename');

pubsubInstance.addChannel('channelName', function (channelPayload) {
  // Handle the notification and its payload
  // If the payload was JSON it has already been parsed for you
});

See that and that.

And you will be able to to the same in Python https://pypi.python.org/pypi/pgpubsub/0.0.2.

Finally, you might want to use data-partitioning in PostgreSQL. Long story short, PostgreSQL has already everything you need