org.apache.hadoop.hbase.master.balancer

Class DoubleArrayCost

java.lang.Object

org.apache.hadoop.hbase.master.balancer.DoubleArrayCost

@InterfaceAudience.Private
final class DoubleArrayCost
extends Object

A helper class to compute a scaled cost using org.apache.commons.math3.stat.descriptive.DescriptiveStatistics#DescriptiveStatistics(). It assumes that this is a zero sum set of costs. It assumes that the worst case possible is all of the elements in one region server and the rest having 0.

Field Summary

Fields

Modifier and Type	Field and Description
private double	cost
private double[]	costs
private boolean	costsChanged

Constructor Summary

Constructors

Constructor and Description
DoubleArrayCost()

Method Summary

Modifier and Type	Method and Description
(package private) void	applyCostsChange(Consumer<double[]> consumer) We do not want to introduce a getCosts method to let upper layer get the cost array directly, so here we introduce this method to take a Consumer as parameter, where we will pass the actual cost array in, so you can change the element of the cost array in the Consumer implementation.
private static double	computeCost(double[] stats)
(package private) double	cost()
static double	getMaxSkew(double total, double numServers) Return the max deviation of distribution Compute max as if all region servers had 0 and one had the sum of all costs.
static double	getMinSkew(double total, double numServers) Return the min skew of distribution
private static double	getSum(double[] stats)
(package private) void	prepare(int length)

Methods inherited from class java.lang.Object

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

Field Detail

costs

private double[] costs

costsChanged

private boolean costsChanged

cost

private double cost

Constructor Detail

DoubleArrayCost

DoubleArrayCost()

Method Detail

prepare

void prepare(int length)

applyCostsChange

void applyCostsChange(Consumer<double[]> consumer)

We do not want to introduce a getCosts method to let upper layer get the cost array directly, so here we introduce this method to take a Consumer as parameter, where we will pass the actual cost array in, so you can change the element of the cost array in the Consumer implementation.

Usually, in prepare method, you need to fill all the elements of the cost array, while in regionMoved method, you just need to update the element for the effect region servers.

cost

double cost()

computeCost

private static double computeCost(double[] stats)

getSum

private static double getSum(double[] stats)

getMinSkew

public static double getMinSkew(double total,
                                double numServers)

Return the min skew of distribution

Parameters:

total - is total number of regions

getMaxSkew

public static double getMaxSkew(double total,
                                double numServers)

Return the max deviation of distribution Compute max as if all region servers had 0 and one had the sum of all costs. This must be a zero sum cost for this to make sense.

Parameters:

total - is total number of regions