|Oracle9i Application Developer's Guide - Large Objects (LOBs)
Release 1 (9.0.1)
Part Number A88879-01
Modeling and Design, 11 of 21
You cannot build B-tree or bitmap indexes on a LOB column. However, depending on your application and its usage of the LOB column, you might be able to improve the performance of queries by building indexes specifically attuned to your domain. Oracle8i and higher's extensibility interfaces allow for domain indexing, a framework for implementing such domain specific indexes.
Oracle9i Data Cartridge Developer's Guide, for information on building domain specific indexes.
Depending on the nature of the contents of the LOB column, one of the Oracle interMedia options could also be used for building indexes. For example, if a text document is stored in a CLOB column, you can build a text index (provided by Oracle) to speed up the performance of text-based queries over the CLOB column.
Oracle9i now supports functional indexing on LOB columns. Analogous to extensible/domain indexes on LOB columns, functional indexes are also automatically updated when a DML operation is performed on the LOB column.