1. Existing CDNs Fail to Address these Challenges
No coherence for dynamic content X
Unscalable network monitoring - O(M × N)
M: # of client groups, N: # of server farms
Client from GWU try to access it again?
Even if sparse clients have very sparse requests, it will end up placing replicas on every CDN servers.
Inefficient replication will have two effects: 1. wastes a lot of replication bandwidth, and consequently, update bandwidth;
2. the replicas are not fully utilized. CDN servers have limit storage. So the inefficient replication will cause old content replicas constantly replaced by new content replicas before serving more clients.
Questions on consistent caching: it is another type of hash table for directory scheme with high probability on query success.
It mainly supports fixed # of replicas for each URL, and is not very flexible for hot URLs, have to continuously and manually change the hash functions. Not really used by Akamai, talk w/ Tom Leighton, Chief scientist.
Second, can’t choose optimal locations for replicas
Third, it doesn’t really record the location of replicas. So can’t update them when change occurs.
Non-cooperative replication inefficient