When we say caching like using memcahe or Redis, is this a 1:1 caching between the user and the cache or can we cache 1 item and use it for all user? Some items like a Friend list will be 1:1 a that is unique per user. But if i want to cache the auto complete list for city lookups which can be used by any user, will it just store 1 list in the cache used by all users at same time or doe it need to store 1 list per user?

Is it possible to cache the entire database, all the lookups, all the users, all their photos, etc using memache or redis?

So from the above example: a friend list will be cleared from the cache when the user logs off. But something like city auto complete will stay in the cache 24-7-365, am i correct?