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<2013-03-21> by Lorenzo Bolla

Simple chat with Postgres LISTEN/NOTIFY and Tornado's IOLoop

Postgres supports from version 8.4 a very interesting functionality: LISTEN/NOTIFY allows sending asynchronous messages to clients connected to the database.

As in a normal "chat", a client "subscribed" (LISTEN) to a channel receives all the messages that other clients "sent" (NOTIFY) on that channel.

Since version 9.0, a notification message can have a payload string as long as 8000 bytes.

In order to experiment with this feature, I've implemented a simple chat based on Tornado's IOLoop. Each client subscribes to a channel (or "room" in chat jargon) and listens to it adding a callback to react to a new notification. In the meantime, in another thread, the client is free to write and submit messages to the "room". Here is a screenshot of the chat in action:

chat.png

Figure 1: Chatting at London Chess Candidates 2013

This is the code, available also on gist: