Implementing Siebel Business Applications on DB2 UDB for z/OS > Customizing a Development Environment > Siebel Tools Considerations on DB2 for z/OS >

About Inactivating Unused Indexes

The standard Siebel data model has a large number of indexes that can degrade performance on DB2 for z/OS. This performance degradation can occur because DB2, unlike Oracle and Microsoft SQL Server, stores NULL as one of the indexed values. Each row with a NULL value for an indexed column gets an entry of its record identifier (RID) in the DB2 index.

Because many Siebel tables are related to a large number of other tables, there are many indexes on foreign keys. Where those related tables are not used, DB2 has the indexes for those foreign keys with one entry: NULL. This key entry has a long RID chain comprised of all the RIDS for every row in the table. There is maintenance overhead each time a row is inserted and even more overhead when it is deleted. Therefore, users of DB2 for z/OS are allowed to inactivate unused indexes using Siebel Tools and to remove them in DB2.

CAUTION:  Before deleting indexes, back up your Siebel Repository and the original storage control and schema.sql files that you installed. Keep track of the indexes you delete. If you notice performance degradation after deleting indexes, review your work and restore the repository, storage control file, and schema.sql. If you need help restoring files, create a service request (SR) on OracleMetaLink 3.