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
|
3%
|
300,000
or more
|
6%
|
150,000
or more
|
12%
|
70,000
or more
|
25%
|
30,000
or more
|
50%
|
10,000
or more
|
100%
(*)
|
0 (no
minimum)
|
References
User
documentation : https://docops.ca.com/
YouTube video : https://www.youtube.com/watch?v=PQck8Q1ymCs
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