Cluster Index:

You have to create an index on the cluster key columns after you have created a cluster. The cluster index is an index defined specifically for a cluster. Like an index holds an entry for each cluster key value. To locate a row in a cluster and the cluster index is used to search the cluster key value that points to the data block related with that cluster key value. Thus, Oracle accesses a given row with a minimum of two I/Os (possibly more, depending on the number of levels which must be traversed in the index).

The subsequent Example describes the creation of Clusters

• Create a cluster for the general column.
• Create an index for the cluster
• Create the table along with clusters

Records cannot be inserted without creating indexes.