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In Oracle, clustering is a way of ordering the physical placement of tables on a disk drive in such a way as to speed up I/O access times. This is accomplished by sharing data blocks on the disk. Anything that minimizes I/O or reduces contention in the physical file system will improve the overall performance of the database.

A table cluster can be described as a set of tables that share the same data blocks, and that are grouped together because they share common columns that are often used together. Index cluster tables can be either multi-table or single-table.

When cluster tables are created, Oracle stores all of the rows for each of the tables in the same data blocks. The cluster key value is the value of the cluster key columns for a particular row.

An index cluster uses an index to maintain row sequence, as opposed to a hash cluster, where the symbolic key is hashed to the data block address.

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Related Code Snippets:
  • CLUSTER_ID - CLUSTER_ID returns the cluster identifier of the predicted cluster with the highest p...
  • CLUSTER_PROBABILITY - CLUSTER_PROBABILITY returns a measure of the degree of confidence of members...
  • CLUSTER_SET - CLUSTER_SET returns a varray of objects containing all possible clusters that a give...
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