Implementing Siebel Business Applications on DB2 for z/OS > Customizing a Development Environment > About Using Siebel Tools in a DB2 for z/OS Environment >

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 these related tables are not used, DB2 assigns the indexes for the foreign keys 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 might want to deactivate unused indexes. Do not deactivate unused indexes in Siebel Tools. To deactivate indexes, contact your Oracle sales representative for Oracle Advanced Customer Services to request assistance from Oracle's Application Expert Services.