Memcached with UDP get can handle 400k gets per second (from a facebook engineering note earlier this year) on a single commodity server. Which "decent" DB can

Memcached with UDP get can handle 400k gets per second (from a facebook engineering note earlier this year) on a single commodity server. Which "decent" DB can even approach this even for simple queries? A cache server and DB server simply have different performance priorities. Memcached makes a lot of sense for caching application specific fragments that has application specific expiration policies. Regarding your 2nd point, latency != 1/throughput when you have parallel queries.