I'm looking to implement notifications within my node.js application. I currently use mysql for relational data (users, submissions, comments, etc). I use mongodb for page views only.
To build a notification system, does it make more sense (from a performance standpoint) to use mongodb vs MySQL?
Also, what's the convention for showing new notifications to users? At first, I was thinking that I'd have a notification icon, and they click on it and it does an ajax call to look for all new notifications from the user, but I want to show the user that the icon is actually worth clicking (either with some different color or a bubble with the number of new notifications like Google Plus does).
I could do it when the user logs it, but that would mean the user would only see new notifications when they logged out and back in (because it'd be saved in their session). Should I poll for updates? I'm not sure if that's the recommended method as it seems like overkill to show a single digit (or more depending on the num of notifications).