would like to know how the website like facebook etc.. saved its data in MySQL database. The most interested thing I would like to know is: say, if you have a userID table (which is too large to save in one server), how could you partition the data and save into different servers? even all userID might be saved in one server, user’s friendlist definitely can not be saved in one server. Then, if you need a query which needs the data from several servers, how to do the query? So far as I know, mysql cluster or memcached etc.. will only be helpful for load balance or speed up the query, but for the exact problems I mentioned, I have no idea how it works.
Anyone could provide some info about this? links or technique keywords might be helpful as well.
Its called sharding. Here is info
http://en.wikipedia.org/wiki/Shard_%28database_architecture%29
Other solution is to also not use MySQL. There are NoSQL solutions, mongodb which might do the sharding for you.