Data persistence for pubnub chat using rails

I have a rails app and want to integrate chat + group chat 1: 1. I've seen a few tutorials from pubnub that can be easily added in real time via pub / sub.

On the persistence level, I'm wondering if I should just store chat messages using PostgresQL in the backend ..?

A bit of information, the application is currently in production and serves 50-80K chat requests per day, and now has about 500K messages, I wonder what should I do.

Thansk!