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Hash Clusters cluster table data in a manner similar to normal, index clusters. To find or store a row in a hash cluster, Oracle applies a hash function to the row's cluster key value. The resulting hash value corresponds to a data block in the cluster.All rows with the same key value are stored together on disk.Hash clusters are a better choice than using an indexed table or index cluster when a table is often queried with equality queries (for example, WHERE product_id=123). For such queries, the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the rows.This reduces the amount of I/Os that must be performed to locate and read/write a row of data.