Disk I/O is reduced & access time improves for joins of clustered tables - Oracle Clusters

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• Nirja Shah   -Posted on 02 Sep 15
  - A cluster provides an optional method of storing table data.
  
  - A cluster is made up of a group of tables that share the same data blocks.
  
  - The tables are grouped together because they share common columns and are often used together.
  
  - Because clusters store related rows of different tables together in the same data blocks, properly used clusters offer two primary benefits:
  
  1. Disk I/O is reduced and access time improves for joins of clustered tables.
  
  2. The cluster key is the column, or group of columns, that the clustered tables have in common.
  - You specify the columns of the cluster key when creating the cluster.
  - You subsequently specify the same columns when creating every table added to the cluster.
  - Each cluster key value is stored only once each in the cluster and the cluster index, no matter how many rows of different tables contain the value.

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