Calculating a correct hit ratio is vital for performance analysis and tracking performance over time. IBM has a correct formula in the V3 administration guide in chapter 7. The Getpage/RIO ratio, usually shown as an ‘efficiency’ ratio by online monitors is not meaningful for tracking either system or application performance.

What is a good number for a GP/RIO ratio?? 5:1, 10:1, 50:1?? Obviously, the higher the better, but the numbers are not meaningful.

DB2 V3 and V4 provides the ability to track this at the application accounting record level, by giving us a new field - Asynchronous Pages Read...the pages actually read in by prefetch type activity.