At Spool, we calculate our key metrics in real time. Traditionally, metrics are performed by a batch job (running hourly, daily, etc.). Redis backed bitmaps allow us to perform such calculations in realtime and are extremely space efficient. In a simulation of 128 million users, a typical metric such as “daily unique users” takes less than 50 ms on a MacBook Pro and only takes 16 MB of memory. Spo
![Redis bitmaps - Fast, easy, realtime metrics -](https://cdn-ak-scissors.b.st-hatena.com/image/square/e54fb80882a15bc75c9ddea1543adbc766bba227/height=288;version=1;width=512/https%3A%2F%2Fspoolblog.files.wordpress.com%2F2011%2F11%2Fbitmap_population_count.png%3Fw%3D529)