Facebook has open sourced a new project called MyRocks that brings together its RocksDB database with MySQL. Essentially, it replaces MySQL's standard InnoDB engine and replaces it with RocksDB. The advantage is that RocksDB has been optimized for flash storage, so it speeds performance when data is stored in SSDs. In addition, MyRocks uses fewer I/Os and is easier to compress, defragment, replicate and access.
However, MyRocks does have some drawbacks. It doesn't support foreign keys or full-text indexing. In fact, even Facebook says it will continue to use the standard version of MySQL most of the time.