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.
void	dump(File output) Writes the values of the sample to the given file.
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.
List<Long>	values() Returns a copy of the sample's values.

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

values

public List<Long> values()

Description copied from interface: Sample

Returns a copy of the sample's values.

Specified by:

values in interface Sample

Returns:

a copy of the sample's values

dump

public void dump(File output)
          throws IOException

Description copied from interface: Sample

Writes the values of the sample to the given file.

Specified by:

dump in interface Sample

Parameters:

output - the file to which the values will be written

Throws:

IOException - if there is an error writing the values