What is a cluster ?
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What is a cluster ?
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A cluster is a group of tables that share the same Oracle block for storing data. It is useful in situations where a query involves a join of multiple tables. The tables that form a cluster may have one or more common columns that together form the cluster key at the time of cluster creation.
Clusters enhance the performance of queries based on table joins. In case of clusters, data is fetched from the same block (instead of fetching it from different tables), thereby reducing disk I/Os. Clusters require less storage space because the block, corresponding to a cluster, stores distinct cluster keys. However, clusters should not be used for tables that are accessed frequently on an individual basis.
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