Distributed hash table: Difference between revisions

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{{Short description|Decentralized distributed system with lookup service}}

A '''distributed hash table''' ('''DHT''') is a [[Distributed computing|distributed system]] that provides a lookup service similar to a [[hash table]]. [[Key–value pair]]s are stored in a DHT, and any participating [[node (networking)|node]] can efficiently retrieve the value associated with a given key. The main advantage of a DHT is that nodes can be added or removed with minimum work around re-distributing keys.<ref>{{Cite book |last1=Hota |first1=Chittaranjan |url=https://books.google.com/books?id=5I25BQAAQBAJ |title=Distributed Computing and Internet Technology: 9th International Conference, ICDCIT 2013, Bhubaneswar, India, February 5-8, 2013, Proceedings |last2=Srimani |first2=Pradip K. |date=2013-01-11 |publisher=Springer |isbn=978-3-642-36071-8 |language=en}}</ref> ''Keys'' are unique identifiers which map to particular ''values'', which in turn can be anything from addresses, to [[Electronic document|documents]], to arbitrary [[Data (computing)|data]].<ref name=StoicaEtAl2001>{{Cite journal | last1 = Stoica | first1 = I. | author-link1 = Ion Stoica | last2 = Morris | first2 = R. | last3 = Karger | first3 = D. | author-link3 = David Karger | last4 = Kaashoek | first4 = M. F. | last5 = Balakrishnan | first5 = H. | author-link5 = Hari Balakrishnan | title = Chord: A scalable peer-to-peer lookup service for internet applications | doi = 10.1145/964723.383071 | journal = ACM SIGCOMM Computer Communication Review | volume = 31 | issue = 4 | pages = 149 | year = 2001 | url = http://pdos.csail.mit.edu/papers/chord:sigcomm01/chord_sigcomm.pdf | quote = A value can be an address, a document, or an arbitrary data item. | access-date = 2018-09-18 | archive-date = 2023-07-07 | archive-url = https://wwwweb.googlearchive.comorg/web/20230707080145/https://pdos.csail.mit.edu/papers/chord:sigcomm01/chord_sigcomm.pdf | url-status = live }}</ref> 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 a DHT to [[scale (computing)|scale]] to extremely large numbers of nodes and to handle continual node arrivals, departures, and failures.

https://web.archive.org/web/20230707080145/https://pdos.csail.mit.edu/papers/chord:sigcomm01/chord_sigcomm.pdf | url-status = live }}</ref> 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 a DHT to [[scale (computing)|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 [[anycast]], cooperative [[Web cache|web caching]], [[distributed file system]]s, [[Domain name system|___domain name services]], [[instant messaging]], [[multicast]], and also [[peer-to-peer file sharing]] and [[content distribution]] systems. Notable distributed networks that use DHTs include [[BitTorrent (protocol)|BitTorrent]]'s distributed tracker, the [[Kad network]], the [[Storm botnet]], the [[Tox (protocol)|Tox instant messenger]], [[Freenet]], the [[YaCy]] search engine, and the [[InterPlanetary File System]].