You can run the RUNSTATS utility to
collect current statistics on tables and indexes in a DB2 for z/OS subsystem.
Running this utility provides the optimizer with the most accurate
information with which to generate the best access plan.
In this scenario, you can compare access plans for SQL statements
from packages to determine if performance has improved.
Tip: You should specify as the source a collection
(that is, a group of packages) that contains the access plan and packages
from before the RUNSTATS command was run. You should
specify as the target a collection that contains the
access plans and packages from after the RUNSTATS command
was run.