Social notworking site Facebook has come up with a data cache which runs on flash memory instead of DRAM. Dubbed McDipper it saves money while still delivering higher performance than disk.
The system is a Facebook-built implementation of the popular memcached key-value store the only difference is that runs on flash memory rather than pricier DRAM. Memcached is the open-source key-value store that caches frequently accessed data in memory so applications can access and serve it faster than if it were stored on hard disks.
Facebook runs thousands of memcached servers to power its various applications. The only downside is that it is expensive. McDipper can handle working sets that had very large footprints but moderate to low request rates. It provides up to 20 times the capacity per server and still supports tens of thousands of operations per second.
According to Gigaom, Facebook has deployed McDipper for a handful of these workloads. This has reduced the total number of deployed servers in some pools by as much as 90 per cent while still delivering more than 90 per cent of get responses with sub-millisecond latencies.