Oracle index compression

You can set the index-compression attribute of the <ora-compression> and <ora-index-ddl> elements to true or false.

An index-compression value of true specifies:

• Compression for all columns but the last for unique indexes
• Compression for all columns for non-unique indexes

Depending on which element you set, you can override compression for all indexes in a database, for all indexes on a specific table, or for specific indexes.

• You can override compression options for all indexes in a database by specifying the index-compression attribute of the <ora-compression> element. For general syntax, see the example in the preceding topic, Oracle database compression.
• You can override compression options for all indexes on a specific table by including the index-compression attribute on the <ora-table-compression> element. For example:

  <database>
    ...
    <upgrade>
      <ora-db-ddl>
        <ora-table-ddl table-name="pc_tableName">
          <ora-table-compression index-compression="true|false" />
        </ora-table-ddl>
      </ora-db-ddl>
    </upgrade>
  </database>

• You can override options for a specific index by adding an <ora-index-ddl> element within the <ora-table-ddl> element for the table that has the index. For example:

  <database>
    ...
    <upgrade>
      <ora-db-ddl>
        <ora-table-ddl table-name="pc_tableName">
          <ora-index-ddl index-compression="true|false" key-columns="column1,column2" />
        </ora-table-ddl>
      </ora-db-ddl>
    </upgrade>
  </database>

  Specify an index by setting the key-columns attribute of the <ora-index-ddl> element to a comma-delimited list of key columns in order. Specify DESC after a column name for descending sort order on that column.

The following example specifies the following overrides:

• Index compression for the entire database
• No compression for the pc_Activity index that contains key columns PublicID and Retired in key positions one and two, respectively.
• No compression for any indexes on the pc_Workflow table.

  <database>
    ...
    <upgrade>
      <ora-db-ddl>
        <ora-compression index-compression="true">
        <ora-table-ddl table-name="xx_Activity">
          <ora-index-ddl key-columns="PublicID,Retired" index-compression="false" />
        </ora-table-ddl>
        <ora-table-ddl table-name="xx_Workflow">
          <ora-table-compression index-compression="false" />
        </ora-table-ddl>
      </ora-db-ddl>
    </upgrade>
  </database>

See also

• The <ora-compression> database configuration element