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Key–value database
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<p>A key–value database, or key–value store, is a data storage paradigm designed for storing, retrieving, and managing <a href="/facts/Associative_array/IFGd2xcP">associative arrays</a>, and a <a href="/facts/Data_structure/yNsNvL1I">data structure</a> more commonly known today as a <i>dictionary</i> or <i><a href="/facts/Hash_table/Ht4ptDPF">hash table</a></i>. Dictionaries contain a <a href="/facts/Collection_(abstract_data_type)/KdjDzR7v">collection</a> of <i><a href="/facts/Object_(computer_science)/eX99dtAw">objects</a></i>, or <i><a href="/facts/Record_(computer_science)/1fvSgenB">records</a></i>, which in turn have many different <i><a href="/facts/Field_(computer_science)/jt622EDb">fields</a></i> within them, each containing data. These records are stored and retrieved using a <i>key</i> that uniquely identifies the record, and is used to find the data within the <a href="/facts/Database/VYcpkevb">database</a>. </p> <p>Key–value databases work in a very different fashion from the better known <a href="/facts/Relational_database/pEKGmJLy">relational databases</a> (RDB). RDBs predefine the data structure in the database as a series of tables containing fields with well defined <a href="/facts/Data_type/fcx5hgVL">data types</a>. Exposing the data types to the database program allows it to apply a number of optimizations. In contrast, key–value systems treat the data as a single opaque collection, which may have different fields for every record. This offers considerable flexibility and more closely follows modern concepts like <a href="/facts/Object-oriented_programming/TxNMEcao">object-oriented programming</a>. Because optional values are not represented by placeholders or input parameters, as in most RDBs, key–value databases often use far less <a href="/facts/Computer_memory/hQKVQ51J">memory</a> to store the same data, which can lead to large performance gains in certain workloads. </p><p>Performance, a lack of standardization and other issues have limited key–value systems to niche uses for many years, but the rapid move to <a href="/facts/Cloud_computing/guhg0FGV">cloud computing</a> after 2010 has led to a renaissance as part of the broader <a href="/facts/NoSQL/vvynRKfd">NoSQL</a> movement. Some <a href="/facts/Graph_database/WJfPlV3z">graph databases</a>, such as <a href="/facts/ArangoDB/72NoJrPM">ArangoDB</a>, are also key–value databases internally, adding the concept of the relationships (<i><a href="/facts/Pointer_(computer_programming)/fPoNzy9b">pointers</a></i>) between records as a first class data type. </p>