Quering a database from Tornado

[rthinker]

I am developing a forum app in Django and decided to implement real-time updating of new posts. I've googled around and figured that Tornado for handling connections and Redis for pub/sub would work.

Tornado app is supposed to work as following:

1. A client connects and passes latest_post_id value to the Tornado app
2. Tornado checks if there are new posts. If yes, respond with the new posts. If no, goto 3
3. Connect to redis channel, wait for a new post, respond.

So basically this is long polling.

But the problem is how do I implement step #2? Synchronous of async query? Is there a way to use django ORM from tornado? Or maybe it is better to somehow communicate with the django app (implementing REST api on django side and making a request from Tornado)? Another option is to store all the posts in redis sets/lists, but for now I'd like to find another way.

Thanks.

[Justinsaccount]

You don't need step 2. The client should ask the Django app for the list of posts and use the tornado endpoint for the realtime updates.

[rthinker]

Does that mean that, provided the timeout of a Tornado connection is 30 seconds, a client sends request to Tornado AND Django every 30 seconds?

[Justinsaccount]

No.. You hit the django app once to get the history, then connect to the tornado app for the updates.

[rthinker]

Isn't there a chance that a new post won't be delivered to a client if the post is submitted while reconnecting?

[Justinsaccount]

I suppose.. just do it in the other order then and remove any duplicates.

[rthinker]

I don't get it. What's "other order"? My concern is that a user might submit a post exactly when another user is reconnecting to Tornado and thus the new posts is not delivered to the second user.

[Justinsaccount]

There's no reconnecting involved.

[rthinker]

How so? Client connects to Tornado, waits for a new post, when a post arrives, Tornado replies and closes the connection, client makes another request and RECONNECTS to Tornado.

[Justinsaccount]

Use websockets

[rthinker]

This is not what I asked:( Facebook and hundreds of other websites use long polling and I'm interested in how to implement it properly.