Package com.codahale.metrics

Class ExponentiallyDecayingReservoir

java.lang.Object

com.codahale.metrics.ExponentiallyDecayingReservoir

All Implemented Interfaces:

Reservoir

public class ExponentiallyDecayingReservoir
extends Object
implements Reservoir

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

Constructors

Constructor	Description
ExponentiallyDecayingReservoir()	Creates a new ExponentiallyDecayingReservoir of 1028 elements, which offers a 99.9% confidence level with a 5% margin of error assuming a normal distribution, and an alpha factor of 0.015, which heavily biases the reservoir to the past 5 minutes of measurements.
ExponentiallyDecayingReservoir(int size, double alpha)	Creates a new ExponentiallyDecayingReservoir.
ExponentiallyDecayingReservoir(int size, double alpha, Clock clock)	Creates a new ExponentiallyDecayingReservoir.

Method Summary

Modifier and Type	Method	Description
Snapshot	getSnapshot()	Returns a snapshot of the reservoir's values.
int	size()	Returns the number of values recorded.
void	update(long value)	Adds a new recorded value to the reservoir.
void	update(long value, long timestamp)	Adds an old value with a fixed timestamp to the reservoir.

Methods inherited from class java.lang.Object

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

Constructor Detail

ExponentiallyDecayingReservoir

public ExponentiallyDecayingReservoir()

Creates a new ExponentiallyDecayingReservoir of 1028 elements, which offers a 99.9% confidence level with a 5% margin of error assuming a normal distribution, and an alpha factor of 0.015, which heavily biases the reservoir to the past 5 minutes of measurements.

ExponentiallyDecayingReservoir

public ExponentiallyDecayingReservoir(int size,
                                      double alpha)

Creates a new ExponentiallyDecayingReservoir.

Parameters:

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

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

ExponentiallyDecayingReservoir

public ExponentiallyDecayingReservoir(int size,
                                      double alpha,
                                      Clock clock)

Creates a new ExponentiallyDecayingReservoir.

Parameters:

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

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

clock - the clock used to timestamp samples and track rescaling

Method Detail

size

public int size()

Description copied from interface: Reservoir

Returns the number of values recorded.

Specified by:

size in interface Reservoir

Returns:

the number of values recorded

update

public void update(long value)

Description copied from interface: Reservoir

Adds a new recorded value to the reservoir.

Specified by:

update in interface Reservoir

Parameters:

value - a new recorded value

update

public void update(long value,
                   long timestamp)

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

Parameters:

value - the value to be added

timestamp - the epoch timestamp of value in seconds

getSnapshot

public Snapshot getSnapshot()

Description copied from interface: Reservoir

Returns a snapshot of the reservoir's values.

Specified by:

getSnapshot in interface Reservoir

Returns:

a snapshot of the reservoir's values