Avoiding manual updates to the catalog statistics

The DB2® data server supports manually updating catalog statistics by issuing UPDATE statements against views in the SYSSTAT schema.

This feature can be useful when mimicking a production database on a test system in order to examine query access plans. The db2look utility is very helpful for capturing the DDL and UPDATE statements against views in the SYSSTAT schema for playback on another system.

Avoid influencing the query optimizer by manually providing incorrect statistics to force a particular query access plan. Although this practice might result in improved performance for some queries, it can result in performance degradation for others. Consider other tuning options (such as using optimization guidelines and profiles) before resorting to this approach. If this approach does become necessary, be sure to record the original statistics in case they need to be restored.