com.yammer.metrics.stats
Class ExponentiallyDecayingSample

java.lang.Object
  com.yammer.metrics.stats.ExponentiallyDecayingSample

All Implemented Interfaces:

Sample

public class ExponentiallyDecayingSample
extends Object
implements Sample

An exponentially-decaying random sample of longs. Uses Cormode et al's forward-decaying priority reservoir sampling method to produce a statistically representative sample, exponentially biased towards newer entries.

See Also:

Cormode et al. Forward Decay: A Practical Time Decay Model for Streaming Systems. ICDE '09: Proceedings of the 2009 IEEE International Conference on Data Engineering (2009)

Constructor Summary

ExponentiallyDecayingSample(int reservoirSize, double alpha)
Creates a new ExponentiallyDecayingSample.

Method Summary

void	clear() Clears all recorded values.
Snapshot	getSnapshot() Returns a snapshot of the sample's values.
int	size() Returns the number of values recorded.
void	update(long value) Adds a new recorded value to the sample.
void	update(long value, long timestamp) Adds an old value with a fixed timestamp to the sample.

Methods inherited from class java.lang.Object

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

Constructor Detail

ExponentiallyDecayingSample

public ExponentiallyDecayingSample(int reservoirSize,
                                   double alpha)

Creates a new ExponentiallyDecayingSample.

Parameters:

reservoirSize - the number of samples to keep in the sampling reservoir

alpha - the exponential decay factor; the higher this is, the more biased the sample will be towards newer values

Method Detail

clear

public void clear()

Description copied from interface: Sample

Clears all recorded values.

Specified by:

clear in interface Sample

size

public int size()

Description copied from interface: Sample

Returns the number of values recorded.

Specified by:

size in interface Sample

Returns:

the number of values recorded

update

public void update(long value)

Description copied from interface: Sample

Adds a new recorded value to the sample.

Specified by:

update in interface Sample

Parameters:

value - a new recorded value

update

public void update(long value,
                   long timestamp)

Adds an old value with a fixed timestamp to the sample.

Parameters:

value - the value to be added

timestamp - the epoch timestamp of value in seconds

getSnapshot

public Snapshot getSnapshot()

Description copied from interface: Sample

Returns a snapshot of the sample's values.

Specified by:

getSnapshot in interface Sample

Returns:

a snapshot of the sample's values