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Analytics: Using Sampling to Reduce Query Times

This article is the last in the series, beginning with Analytics Application - Concepts and Metrics Explained

 

The Analytics Application included in Services Director can apply a Sample Filter to reduce query times. This is because when you navigate interactively through very large analytics datasets, it is sometimes desirable to trade off accuracy against processing time.

The analytics application provides a Sampling Selector control to allow users to do this. This can be applied to any graph except the Dataset View

an7-sampling.png

sampling ratio is the probability of any single event being included in the total result set. For example, if the sampling ratio value is 1:100, each event has a 1 in 100 chance of being included in the results. The selection of each event is independent. As a result, it is possible that many events will be included from the first 100 events, or that none of these events will be included.

NOTE- If you re-run a sampling search, it is virtually certain that different specific results will be returned. 

A range of sampling ratios from1:10 to 1:10000 are supported in Services Director:

  • 1:10 sampling ratio retrieves the most data for a given dataset, and is the most representative of source data.
  • A sampling ratio of 1:10000 retrieves the least data for a given dataset, and is therefore less representative. 
  • A sampling ratio of 1:1 is also supported, which indicates that all data is included. That is, that there is no sampling

If sampling is required, your search should always retrieve as much data as practical. That is, if a 1:10 sampling ratio produces acceptable results, do not proceed to using a 1:100 sampling ratio.

NOTE - Where analytics events are used to calculate totals (such as throughput, and requests per second), sampling should be used with caution. All displayed totals will be approximated for the entiredataset based on the sample. As the sampling ratio increases, the accuracy of this approximation decreases.

All of the standard controls/filters are applied when using sampling. Note that:

  • The sampling ratio also affects the query performed for the Component Filter. This can result in the Component Filter  'missing' some values that are present in the dataset, particularly when using sampling on smaller datasets, or when using higher sampling rates.  
  • Where a sampled set of results does not include a selected value for a specific Component Filter category, the selected value for the filter is de-selected.

 

 

This article is the last in the series, beginning with Analytics Application - Concepts and Metrics Explained

Prev: Using the Component Filter to Refine Queries

 

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Revision #:
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Last update:
‎06-15-2018 03:10:AM
Updated by:
 
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