Distributed hash table - Wikipedia, the free encyclopedia

Description

Distributed hash tables ( DHTs ) are a class of decentralized distributed systems that provide a lookup service similar to a hash table : ( key , value ) pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key. Responsibility for maintaining the mapping from keys to values is distributed among the nodes, in such a way that a change in the set of participants causes a minimal amount of disruption. This allows DHTs to scale to extremely large numbers of nodes and to handle continual node arrivals, departures, and failures.

DHTs form an infrastructure that can be used to build more complex services, such as distributed file systems , peer-to-peer file sharing and content distribution systems, cooperative web caching , multicast , anycast , domain name services , and instant messaging . Notable distributed networks that use DHTs include BitTorrent 's distributed tracker, the eDonkey network , the Storm botnet , YaCy , and the Coral Content Distribution Network .

History

DHT research was originally motivated, in part, by peer-to-peer systems such as Napster , Gnutella , and Freenet , which took advantage of resources distributed across the Internet to provide a single useful application. In particular, they took advantage of increased bandwidth and hard disk capacity to provide a file sharing service.

These systems differed in how they found the data their peers contained:

Napster had a central index server: each node, upon joining, would send a list of locally held files to the server, which would perform searches and refer the querier to the nodes that held the results. This central component left the system vulnerable to attacks and lawsuits.

Gnutella and similar networks moved to a flooding query model—in essence, each search would result in a message being broadcast to ...

Original URL

http://en.wikipedia.org/wiki/Distributed_hash_table

http://en.wikipedia.org/wiki/Distributed_hash_table