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A column of a distributed data store is a NoSQL object of the lowest level in a keyspace. It is a tuple (a key-value pair) consisting of three elements: * Unique name: Used to reference the column * Value: The content of the column. It can have different types, like AsciiType, LongType, TimeUUIDType, UTF8Type among others.* Timestamp: The system timestamp used to determine the valid content. ==Usage== The column is used as a store for the value and has a timestamp that is used to differentiate the valid content from stale ones. According to the CAP theorem, distributed data stores cannot guarantee consistency, as availability and partition tolerance are more important issues. Therefore, the data store or the application programmer will use the timestamp to find out which of the stored values in the backup nodes are up-to-date. Some data stores, like Riak, may use the more sophisticated vector clock instead of the timestamp to resolve stale information. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Column (data store)」の詳細全文を読む スポンサード リンク
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