Java tutorial
/** * Copyright 2016 Yahoo Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.yahoo.pulsar.broker.loadbalance.impl; import java.util.HashMap; import java.util.Map; import java.util.TreeSet; import org.apache.commons.lang3.tuple.ImmutablePair; import org.apache.commons.lang3.tuple.Pair; import com.yahoo.pulsar.broker.BrokerData; import com.yahoo.pulsar.broker.ServiceConfiguration; import com.yahoo.pulsar.broker.loadbalance.LoadData; import com.yahoo.pulsar.broker.loadbalance.LoadSheddingStrategy; /** * An abstract class which makes a LoadSheddingStrategy which makes decisions based on standard deviation easier to * implement. Assuming there exists some real number metric which may estimate the load on a server, this load shedding * strategy calculates the standard deviation with respect to that metric and sheds load on brokers whose standard * deviation is above some threshold. */ public abstract class DeviationShedder implements LoadSheddingStrategy { // A Set of pairs is used in favor of a Multimap for simplicity. protected TreeSet<Pair<Double, String>> metricTreeSetCache; protected TreeSet<Pair<Double, String>> bundleTreeSetCache; /** * Initialize this DeviationShedder. */ public DeviationShedder() { bundleTreeSetCache = new TreeSet<>(); metricTreeSetCache = new TreeSet<>(); } // Measure the load incurred by a bundle. protected abstract double bundleValue(String bundle, BrokerData brokerData, ServiceConfiguration conf); // Measure the load suffered by a broker. protected abstract double brokerValue(BrokerData brokerData, ServiceConfiguration conf); // Get the threshold above which the standard deviation of a broker is large // enough to warrant unloading bundles. protected abstract double getDeviationThreshold(ServiceConfiguration conf); /** * Recommend that all of the returned bundles be unloaded based on observing excessive standard deviations according * to some metric. * * @param loadData * The load data to used to make the unloading decision. * @param conf * The service configuration. * @return A map from all selected bundles to the brokers on which they reside. */ @Override public Map<String, String> findBundlesForUnloading(final LoadData loadData, final ServiceConfiguration conf) { final Map<String, String> result = new HashMap<>(); bundleTreeSetCache.clear(); metricTreeSetCache.clear(); double sum = 0; double squareSum = 0; final Map<String, BrokerData> brokerDataMap = loadData.getBrokerData(); // Treating each broker as a data point, calculate the sum and squared // sum of the evaluated broker metrics. // These may be used to calculate the standard deviation. for (Map.Entry<String, BrokerData> entry : brokerDataMap.entrySet()) { final double value = brokerValue(entry.getValue(), conf); sum += value; squareSum += value * value; metricTreeSetCache.add(new ImmutablePair<>(value, entry.getKey())); } // Mean cannot change by just moving around bundles. final double mean = sum / brokerDataMap.size(); double standardDeviation = Math.sqrt(squareSum / brokerDataMap.size() - mean * mean); final double deviationThreshold = getDeviationThreshold(conf); String lastMostOverloaded = null; // While the most loaded broker is above the standard deviation // threshold, continue to move bundles. while ((metricTreeSetCache.last().getKey() - mean) / standardDeviation > deviationThreshold) { final Pair<Double, String> mostLoadedPair = metricTreeSetCache.last(); final double highestValue = mostLoadedPair.getKey(); final String mostLoaded = mostLoadedPair.getValue(); final Pair<Double, String> leastLoadedPair = metricTreeSetCache.first(); final double leastValue = leastLoadedPair.getKey(); final String leastLoaded = metricTreeSetCache.first().getValue(); if (!mostLoaded.equals(lastMostOverloaded)) { // Reset the bundle tree set now that a different broker is // being considered. bundleTreeSetCache.clear(); for (String bundle : brokerDataMap.get(mostLoaded).getLocalData().getBundles()) { if (!result.containsKey(bundle)) { // Don't consider bundles that are already going to be // moved. bundleTreeSetCache.add(new ImmutablePair<>( bundleValue(bundle, brokerDataMap.get(mostLoaded), conf), bundle)); } } lastMostOverloaded = mostLoaded; } boolean selected = false; while (!(bundleTreeSetCache.isEmpty() || selected)) { Pair<Double, String> mostExpensivePair = bundleTreeSetCache.pollLast(); double loadIncurred = mostExpensivePair.getKey(); // When the bundle is moved, we want the now least loaded server // to have lower overall load than the // most loaded server does not. Thus, we will only consider // moving the bundle if this condition // holds, and otherwise we will try the next bundle. if (loadIncurred + leastValue < highestValue) { // Update the standard deviation and replace the old load // values in the broker tree set with the // load values assuming this move took place. final String bundleToMove = mostExpensivePair.getValue(); result.put(bundleToMove, mostLoaded); metricTreeSetCache.remove(mostLoadedPair); metricTreeSetCache.remove(leastLoadedPair); final double newHighLoad = highestValue - loadIncurred; final double newLowLoad = leastValue - loadIncurred; squareSum -= highestValue * highestValue + leastValue * leastValue; squareSum += newHighLoad * newHighLoad + newLowLoad * newLowLoad; standardDeviation = Math.sqrt(squareSum / brokerDataMap.size() - mean * mean); metricTreeSetCache.add(new ImmutablePair<>(newLowLoad, leastLoaded)); metricTreeSetCache.add(new ImmutablePair<>(newHighLoad, mostLoaded)); selected = true; } } if (!selected) { // Move on to the next broker if no bundle could be moved. metricTreeSetCache.pollLast(); } } return result; } }