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We use (and pay for) Parse at the moment but it's really slow for us despite the very little amount of data we send to them and caching locally is a big pain.
1. Based on the real time data from Google Analytics. E.g. no one day time lag. No data from crawling the web.
2. Use Google Analytics Real Time API or something else approved by Google so it isn't going to get Google blocking my analytics account.
3. Only posts referrers that have never been seen before, or never been seen for some trailing X day window.