Package com.codahale.metrics

Class UniformReservoir

java.lang.Object

com.codahale.metrics.UniformReservoir

All Implemented Interfaces:

Reservoir

public class UniformReservoir
extends Object
implements Reservoir

A random sampling reservoir of a stream of longs. Uses Vitter's Algorithm R to produce a statistically representative sample.

See Also:

• Random Sampling with a Reservoir

Field Summary

Fields

Modifier and Type	Field	Description
private static final int	BITS_PER_LONG
private final AtomicLong	count
private static final int	DEFAULT_SIZE
private final AtomicLongArray	values

Constructor Summary

Constructors

Constructor	Description
UniformReservoir()	Creates a new UniformReservoir of 1028 elements, which offers a 99.9% confidence level with a 5% margin of error assuming a normal distribution.
UniformReservoir(int size)	Creates a new UniformReservoir.

Method Summary

Modifier and Type	Method	Description
Snapshot	getSnapshot()	Returns a snapshot of the reservoir's values.
private static long	nextLong(long n)	Get a pseudo-random long uniformly between 0 and n-1.
int	size()	Returns the number of values recorded.
void	update(long value)	Adds a new recorded value to the reservoir.

Methods inherited from class java.lang.Object

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

Field Details

DEFAULT_SIZE

private static final int DEFAULT_SIZE

See Also:

• Constant Field Values

BITS_PER_LONG

private static final int BITS_PER_LONG

See Also:

• Constant Field Values

count

private final AtomicLong count

values

private final AtomicLongArray values

Constructor Details

UniformReservoir

public UniformReservoir()

Creates a new UniformReservoir of 1028 elements, which offers a 99.9% confidence level with a 5% margin of error assuming a normal distribution.

UniformReservoir

public UniformReservoir(int size)

Creates a new UniformReservoir.

Parameters:

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

Method Details

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

nextLong

private static long nextLong(long n)

Get a pseudo-random long uniformly between 0 and n-1. Stolen from Random.nextInt().

Parameters:

n - the bound

Returns:

a value select randomly from the range [0..n).

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