org.apache.cassandra.metrics

Class FrequencySampler<T>

java.lang.Object

org.apache.cassandra.metrics.Sampler<T>

org.apache.cassandra.metrics.FrequencySampler<T>

Type Parameters:

T -

public abstract class FrequencySampler<T>
extends Sampler<T>

Find the most frequent sample. A sample adds to the sum of its key ie

add("x", 10); and add("x", 20); will result in "x" = 30

This uses StreamSummary to only store the approximate cardinality (capacity) of keys. If the number of distinct keys exceed the capacity, the error of the sample may increase depending on distribution of keys among the total set.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.cassandra.metrics.Sampler

Sampler.Sample<S>, Sampler.SamplerType

Constructor Summary

Constructors

Constructor and Description
FrequencySampler()

Method Summary

Modifier and Type	Method and Description
void	beginSampling(int capacity, int durationMillis) Start to record samples
java.util.List<Sampler.Sample<T>>	finishSampling(int count) Call to stop collecting samples, and gather the results
protected void	insert(T item, long value)
boolean	isEnabled()

Methods inherited from class org.apache.cassandra.metrics.Sampler

addSample, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FrequencySampler

public FrequencySampler()

Method Detail

beginSampling

public void beginSampling(int capacity,
                          int durationMillis)

Start to record samples

Specified by:

beginSampling in class Sampler<T>

Parameters:

capacity - Number of sample items to keep in memory, the lower this is the less accurate results are. For best results use value close to cardinality, but understand the memory trade offs.

finishSampling

public java.util.List<Sampler.Sample<T>> finishSampling(int count)

Call to stop collecting samples, and gather the results

Specified by:

finishSampling in class Sampler<T>

Parameters:

count - Number of most frequent items to return

insert

protected void insert(T item,
                      long value)

Specified by:

insert in class Sampler<T>

isEnabled

public boolean isEnabled()

Specified by:

isEnabled in class Sampler<T>