Cache issues
	Invalidation - how do you tell a cache request that its no longer valid ? 
		Same user requests the same information multiple times, or multiple users
		request the same information. 
		There must be a proper way to get informed that the information held by 
		a cache needs to be discarded.
	Eviction - Asking a question after invalidation
		how long do i exist after cache invalidation? 
	Naming - what couples Invalidation & Eviction 
		immutable cache key = {cache-name}-{uid}-{cache-version}-{logical-timestamp}
	
								 local cache
	coherence - load balancer -> local cache -> memcache
								 local cache