Realtime metrics using Redis bitmaps

It is very good to see this article and Redis bitmaps exploited, since it is an extremely memory efficient way to store data, and given the encoding, it is extremely fast to also fetch big amount of information this way.<p>I really suggest to also looking at GETRANGE and SETRANGE operations that allow to access sub-ranges of a large bitmap fetching or setting arbitrary ranges fo bits.<p>Probably Lua scripting in 2.6 will enable a lot more interesting things combining server side execution and bitmaps. Thanks for sharing this work.

How does it compare with just using sets? Usually only a small fraction of your total userbase is online any given day, especially as dead accounts accumulate... wouldn't the bitmaps be inefficiently sparse?

Here's a quick ruby implementation:<p><a href="https://github.com/cmdrkeene/bitmap-counter" rel="nofollow">https://github.com/cmdrkeene/bitmap-counter</a>

An honest question: what use are realtime metrics if you can't act on them in realtime? If it takes a day or more to gather enough data to make a decision and react to it with code or otherwise, then anything more than daily metrics seem like a distraction. I suppose it can be useful if you have some automated systems in place or if you're using it for alarms.

How do they know that user ids are contiguous?

Compressed bitmaps would be cool too.

Cool!