Default value for pool hit ratio

[gnadimut]

Hi,

In one of the scenario, the pool hit ratio is -98%. What is the thresold for buffer pool hit ratio. If -98% is unacceptable, how can improve the buffer pool hit ratio.

Thanks
Gokul.N

[db2xpert]

The first thing to try to understand is that Hit Ratios are irrelevant as performance metrics. They cannot be converted into application elapsed time components, or into CPU seconds.
You need to focus on the IO rate/second as a real measure of system/pool/application performance.

For DB2 z/OS, there have been two hit ratio formulas in use over the years.

Application Hit (getpages - read IOs)/getpages totally useless

System Hit (getpages - SumOfAllPagesRe ad)/getpages this is somewhat indicative of pool performance, but there can be miinimal changes in the % but still a significant change in the underlying IO rate/sec. I am the author of this formula about 20 years ago, and this is the formula used in the IBM manuals today.

You can look at my papers and presentations on
www.responsives ystems.com
for in depth explanations of buffer pool performance and tuning perspectives.

Joel