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Distributed hash table
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<p>A distributed hash table (DHT) is a <a href="/facts/Distributed_computing/o5nyhqTF">distributed system</a> that provides a lookup service similar to a <a href="/facts/Hash_table/Ht4ptDPF">hash table</a>. <a href="/facts/Key%E2%80%93value_pair/buweLY96">Key–value pairs</a> are stored in a DHT, and any participating <a href="/facts/Node_(networking)/LBp2vNcJ">node</a> 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. <i>Keys</i> are unique identifiers which map to particular <i>values</i>, which in turn can be anything from addresses, to <a href="/facts/Electronic_document/7ee80Ee4">documents</a>, to arbitrary <a href="/facts/Data_(computing)/cPjfFHph">data</a>. 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 <a href="/facts/Scale_(computing)/jh7JomPa">scale</a> to extremely large numbers of nodes and to handle continual node arrivals, departures, and failures. </p><p>DHTs form an infrastructure that can be used to build more complex services, such as <a href="/facts/Anycast/d6lUjbno">anycast</a>, cooperative <a href="/facts/Web_cache/DqIBcWem">web caching</a>, <a href="/facts/Distributed_file_system/Bz61f7Ce">distributed file systems</a>, <a href="/facts/Domain_name_system/rfxdWFsj">domain name services</a>, <a href="/facts/Instant_messaging/8lwwDyjK">instant messaging</a>, <a href="/facts/Multicast/D9IspSfl">multicast</a>, and also <a href="/facts/Peer-to-peer_file_sharing/em1qEY3C">peer-to-peer file sharing</a> and <a href="/facts/Content_distribution/9gbe83sK">content distribution</a> systems. Notable distributed networks that use DHTs include <a href="/facts/BitTorrent_(protocol)/HP9ChWWW">BitTorrent</a>'s distributed tracker, the <a href="/facts/Kad_network/032YPJyz">Kad network</a>, the <a href="/facts/Storm_botnet/vQlobWn1">Storm botnet</a>, the <a href="/facts/Tox_(protocol)/2l3uuyE8">Tox instant messenger</a>, <a href="/facts/Freenet/VrRhhcDc">Freenet</a>, the <a href="/facts/YaCy/bD8Ytze8">YaCy</a> search engine, and the <a href="/facts/InterPlanetary_File_System/VUhdLRdm">InterPlanetary File System</a>. </p>