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HBASE-24140 : Move CandidateGenerator and their implementors out of StochasticLoadBalancer (#1458)
Signed-off-by: Jan Hentschel <jan.hentschel@ultratendency.com>
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‎hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/CandidateGenerator.java‎

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/*
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.hadoop.hbase.master.balancer;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.List;
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import java.util.Map;
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import org.apache.hadoop.hbase.client.RegionInfo;
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import org.apache.yetus.audience.InterfaceAudience;
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/**
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* Generates a candidate action to be applied to the cluster for cost function search
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*/
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@InterfaceAudience.Private
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abstract class CandidateGenerator {
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abstract BaseLoadBalancer.Cluster.Action generate(BaseLoadBalancer.Cluster cluster);
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/**
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* From a list of regions pick a random one. Null can be returned which
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* {@link StochasticLoadBalancer#balanceCluster(Map)} recognize as signal to try a region move
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* rather than swap.
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*
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* @param cluster The state of the cluster
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* @param server index of the server
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* @param chanceOfNoSwap Chance that this will decide to try a move rather
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* than a swap.
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* @return a random {@link RegionInfo} or null if an asymmetrical move is
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* suggested.
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*/
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int pickRandomRegion(BaseLoadBalancer.Cluster cluster, int server,
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double chanceOfNoSwap) {
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// Check to see if this is just a move.
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if (cluster.regionsPerServer[server].length == 0
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|| StochasticLoadBalancer.RANDOM.nextFloat() < chanceOfNoSwap) {
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// signal a move only.
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return -1;
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}
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int rand = StochasticLoadBalancer.RANDOM.nextInt(cluster.regionsPerServer[server].length);
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return cluster.regionsPerServer[server][rand];
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}
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int pickRandomServer(BaseLoadBalancer.Cluster cluster) {
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if (cluster.numServers < 1) {
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return -1;
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}
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return StochasticLoadBalancer.RANDOM.nextInt(cluster.numServers);
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}
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int pickRandomRack(BaseLoadBalancer.Cluster cluster) {
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if (cluster.numRacks < 1) {
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return -1;
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}
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return StochasticLoadBalancer.RANDOM.nextInt(cluster.numRacks);
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}
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int pickOtherRandomServer(BaseLoadBalancer.Cluster cluster, int serverIndex) {
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if (cluster.numServers < 2) {
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return -1;
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}
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while (true) {
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int otherServerIndex = pickRandomServer(cluster);
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if (otherServerIndex != serverIndex) {
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return otherServerIndex;
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}
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}
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}
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int pickOtherRandomRack(BaseLoadBalancer.Cluster cluster, int rackIndex) {
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if (cluster.numRacks < 2) {
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return -1;
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}
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while (true) {
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int otherRackIndex = pickRandomRack(cluster);
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if (otherRackIndex != rackIndex) {
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return otherRackIndex;
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}
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}
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}
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BaseLoadBalancer.Cluster.Action pickRandomRegions(BaseLoadBalancer.Cluster cluster,
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int thisServer, int otherServer) {
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if (thisServer < 0 || otherServer < 0) {
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return BaseLoadBalancer.Cluster.NullAction;
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}
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// Decide who is most likely to need another region
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int thisRegionCount = cluster.getNumRegions(thisServer);
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int otherRegionCount = cluster.getNumRegions(otherServer);
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// Assign the chance based upon the above
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double thisChance = (thisRegionCount > otherRegionCount) ? 0 : 0.5;
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double otherChance = (thisRegionCount <= otherRegionCount) ? 0 : 0.5;
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int thisRegion = pickRandomRegion(cluster, thisServer, thisChance);
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int otherRegion = pickRandomRegion(cluster, otherServer, otherChance);
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return getAction(thisServer, thisRegion, otherServer, otherRegion);
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}
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protected BaseLoadBalancer.Cluster.Action getAction(int fromServer, int fromRegion,
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int toServer, int toRegion) {
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if (fromServer < 0 || toServer < 0) {
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return BaseLoadBalancer.Cluster.NullAction;
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}
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if (fromRegion > 0 && toRegion > 0) {
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return new BaseLoadBalancer.Cluster.SwapRegionsAction(fromServer, fromRegion,
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toServer, toRegion);
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} else if (fromRegion > 0) {
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return new BaseLoadBalancer.Cluster.MoveRegionAction(fromRegion, fromServer, toServer);
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} else if (toRegion > 0) {
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return new BaseLoadBalancer.Cluster.MoveRegionAction(toRegion, toServer, fromServer);
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} else {
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return BaseLoadBalancer.Cluster.NullAction;
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}
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}
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/**
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* Returns a random iteration order of indexes of an array with size length
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*/
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List<Integer> getRandomIterationOrder(int length) {
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ArrayList<Integer> order = new ArrayList<>(length);
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for (int i = 0; i < length; i++) {
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order.add(i);
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}
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Collections.shuffle(order);
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return order;
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}
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}

‎hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/FavoredStochasticBalancer.java‎

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* RegionServer as the new Primary RegionServer) after a region is recovered. This
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* should help provide consistent read latencies for the regions even when their
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* primary region servers die. This provides two
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* {@link org.apache.hadoop.hbase.master.balancer.StochasticLoadBalancer.CandidateGenerator}
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* {@link CandidateGenerator}
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*
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*/
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@InterfaceAudience.Private

‎hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/LoadCandidateGenerator.java‎

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/*
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.hadoop.hbase.master.balancer;
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import org.apache.yetus.audience.InterfaceAudience;
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@InterfaceAudience.Private
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class LoadCandidateGenerator extends CandidateGenerator {
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@Override
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BaseLoadBalancer.Cluster.Action generate(BaseLoadBalancer.Cluster cluster) {
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cluster.sortServersByRegionCount();
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int thisServer = pickMostLoadedServer(cluster, -1);
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int otherServer = pickLeastLoadedServer(cluster, thisServer);
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return pickRandomRegions(cluster, thisServer, otherServer);
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}
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private int pickLeastLoadedServer(final BaseLoadBalancer.Cluster cluster, int thisServer) {
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Integer[] servers = cluster.serverIndicesSortedByRegionCount;
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int index = 0;
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while (servers[index] == null || servers[index] == thisServer) {
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index++;
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if (index == servers.length) {
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return -1;
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}
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}
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return servers[index];
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}
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private int pickMostLoadedServer(final BaseLoadBalancer.Cluster cluster, int thisServer) {
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Integer[] servers = cluster.serverIndicesSortedByRegionCount;
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int index = servers.length - 1;
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while (servers[index] == null || servers[index] == thisServer) {
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index--;
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if (index < 0) {
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return -1;
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}
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}
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return servers[index];
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}
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}

‎hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/LocalityBasedCandidateGenerator.java‎

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/*
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.hadoop.hbase.master.balancer;
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import org.apache.hadoop.hbase.master.MasterServices;
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import org.apache.hbase.thirdparty.com.google.common.base.Optional;
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import org.apache.yetus.audience.InterfaceAudience;
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@InterfaceAudience.Private
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class LocalityBasedCandidateGenerator extends CandidateGenerator {
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private MasterServices masterServices;
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LocalityBasedCandidateGenerator(MasterServices masterServices) {
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this.masterServices = masterServices;
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}
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@Override
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BaseLoadBalancer.Cluster.Action generate(BaseLoadBalancer.Cluster cluster) {
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if (this.masterServices == null) {
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int thisServer = pickRandomServer(cluster);
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// Pick the other server
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int otherServer = pickOtherRandomServer(cluster, thisServer);
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return pickRandomRegions(cluster, thisServer, otherServer);
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}
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// Randomly iterate through regions until you find one that is not on ideal host
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for (int region : getRandomIterationOrder(cluster.numRegions)) {
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int currentServer = cluster.regionIndexToServerIndex[region];
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if (currentServer != cluster.getOrComputeRegionsToMostLocalEntities(
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BaseLoadBalancer.Cluster.LocalityType.SERVER)[region]) {
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Optional<BaseLoadBalancer.Cluster.Action> potential = tryMoveOrSwap(cluster,
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currentServer, region,
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cluster.getOrComputeRegionsToMostLocalEntities(
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BaseLoadBalancer.Cluster.LocalityType.SERVER)[region]
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);
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if (potential.isPresent()) {
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return potential.get();
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}
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}
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}
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return BaseLoadBalancer.Cluster.NullAction;
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}
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private Optional<BaseLoadBalancer.Cluster.Action> tryMoveOrSwap(BaseLoadBalancer.Cluster cluster,
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int fromServer, int fromRegion, int toServer) {
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// Try move first. We know apriori fromRegion has the highest locality on toServer
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if (cluster.serverHasTooFewRegions(toServer)) {
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return Optional.of(getAction(fromServer, fromRegion, toServer, -1));
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}
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// Compare locality gain/loss from swapping fromRegion with regions on toServer
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double fromRegionLocalityDelta = getWeightedLocality(cluster, fromRegion, toServer)
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- getWeightedLocality(cluster, fromRegion, fromServer);
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for (int toRegionIndex : getRandomIterationOrder(cluster.regionsPerServer[toServer].length)) {
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int toRegion = cluster.regionsPerServer[toServer][toRegionIndex];
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double toRegionLocalityDelta = getWeightedLocality(cluster, toRegion, fromServer)
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- getWeightedLocality(cluster, toRegion, toServer);
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// If locality would remain neutral or improve, attempt the swap
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if (fromRegionLocalityDelta + toRegionLocalityDelta >= 0) {
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return Optional.of(getAction(fromServer, fromRegion, toServer, toRegion));
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}
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}
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return Optional.absent();
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}
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private double getWeightedLocality(BaseLoadBalancer.Cluster cluster, int region, int server) {
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return cluster.getOrComputeWeightedLocality(region, server,
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BaseLoadBalancer.Cluster.LocalityType.SERVER);
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}
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void setServices(MasterServices services) {
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this.masterServices = services;
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}
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}

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