How does/did Facebook use memcache and mySQL in 2009? — No joins in production. They have many logical databases for all of their types: people, events, place info, etc. They treat the web tier as a CPU, memcache as system memory, and the database as disk. Everything has an ID and you use the ID to query memcache using a multiget. Any misses are fetched from the database and cached in memcache.