IBM BPM, V8.0.1, All platforms > Tuning > Advanced tuning > Database: DB2 for z/OS specific tuning
Maintain proper table indexing
Although the Business Process Management products create a set of database indexes that are appropriate for many installations, additional indexes are required in some circumstances.
A database environment that requires additional indexes often displays performance degradation over time; in some cases the performance degradation
can be profound. Environments that need additional indexes often exhibit
heavy read I/O on devices holding the table space containers. To assist
in determining which additional indexes could improve performance, DB2 provides a set of tools (such
as the Optimization Service Center for DB2 for z/OS and DB2 Optimization Expert for z/OS) to help define and design indexes that are suitable for a particular workload. See: 
http://www-01.ibm.com/software/data/db2imstools/db2tools/accessories-suite/.