Creating an index using key compression - Oracle Indexes and Partitioned Tables

Q.  Creating an index using key compression enables you to eliminate repeated occurrences of key column prefix values.
- Published on 12 Aug 15

a. True
b. False

ANSWER: True
 

    Discussion

  • Nirja Shah   -Posted on 28 Sep 15
    - Creating an index using key compression enables you to eliminate repeated occurrences of key column prefix values.

    - Key compression breaks an index key into a prefix and a suffix entry.

    - Compression is achieved by sharing the prefix entries among all the suffix entries in an index block.

    - This sharing can lead to huge savings in space, allowing you to store more keys for each index block while improving performance.

    - Key compression can be useful in the following situations:
    - You have a non-unique index where ROWID is appended to make the key unique. If you use key compression here, the duplicate key is stored as a prefix entry on the index block without the ROWID. The remaining rows become suffix entries consisting of only the ROWID.
    - You have a unique multicolumn index.

    - You enable key compression using the COMPRESS clause.

    - The prefix length (as the number of key columns) can also be specified to identify how the key columns are broken into a prefix and suffix entry.

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