org.apache.cassandra.utils

Class TopKSampler<T>

java.lang.Object

org.apache.cassandra.utils.TopKSampler<T>

public class TopKSampler<T>
extends java.lang.Object

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TopKSampler.SamplerResult<S> Represents the cardinality and the topK ranked items collected during a sample period

Constructor Summary

Constructors

Constructor and Description
TopKSampler()

Method Summary

Modifier and Type	Method and Description
void	addSample(T item)
void	addSample(T item, long hash, int value) Adds a sample to statistics collection.
void	beginSampling(int capacity) Start to record samples
TopKSampler.SamplerResult<T>	finishSampling(int count) Call to stop collecting samples, and gather the results

Methods inherited from class java.lang.Object

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

Constructor Detail

TopKSampler

public TopKSampler()

Method Detail

beginSampling

public void beginSampling(int capacity)

Start to record samples

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 TopKSampler.SamplerResult<T> finishSampling(int count)

Call to stop collecting samples, and gather the results

Parameters:

count - Number of most frequent items to return

addSample

public void addSample(T item)

addSample

public void addSample(T item,
                      long hash,
                      int value)

Adds a sample to statistics collection. This method is non-blocking and will use the "Sampler" thread pool to record results if the sampler is enabled. If not sampling this is a NOOP