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Buffer Pool Hit Ratio

Buffer Pool Hit Ratio

  • The System Hit Ratio Calculation is: (Getpages - Pages Read) / Getpages
  • This is also available at the Application Accounting Level with Version 3
  • A Getpage/RIO calculation is not generally Meaningful - What is a good number?? 50:1 70:1?
    • This is an Application Hit Ratio...

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Notes:

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.