Thursday, June 1, 2017

Use Getpage Sampling to improve performance of CA Subsystem Analyzer

Reducing Collection Overhead

When it comes to DB2 performance products, customers are often demanding reduction in the overhead associated. Available in CA DB2 Tools 19, CA Subsystem Analyzer now allows to activate Getpage Sampling feature.

Sampling getpage requests reduces collection overhead significantly. Instead of capturing all getpages for databases, tablespaces, tables, indexes, datasets, and dataset extents, the percentage that you select is sampled. With sampling enabled, getpage count values are approximated. The sampling process is based on proven sample size and correction for finite population calculations using a confidence level of 95 percent and a confidence interval of 1 percent. Therefore, the approximated values are within 1 percent of the actual values 95 percent of the time when sufficient getpage activity occurs during an interval.

Watch the video

This feature is explained in a video, available in YouTube :

Recommended Sampling Rate

3 percent sampling rate results in the highest reduction of collection overhead. However, accuracy must be considered when choosing a sampling rate. The table below shows the recommended sampling rate for the number of actual getpage requests per object that you expect to occur per interval. Using the recommended sampling rate ensures accurate getpage counts. For example, if you expect 30,000 or more getpages for each object, specify 25. One out of every four getpages is sampled.

Recommended Sampling Rate
Getpages Per Object Expected
300,000 or more
150,000 or more
70,000 or more
30,000 or more
10,000 or more
100% (*)
0 (no minimum)


User documentation :

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