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HBASE-28513 The StochasticLoadBalancer should support discrete evalua…
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Ray Mattingly
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Jan 17, 2025
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...-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/BalancerConditionals.java
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| /* | ||
| * Licensed to the Apache Software Foundation (ASF) under one | ||
| * or more contributor license agreements. See the NOTICE file | ||
| * distributed with this work for additional information | ||
| * regarding copyright ownership. The ASF licenses this file | ||
| * to you 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 org.apache.hadoop.hbase.master.balancer; | ||
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| import java.lang.reflect.Constructor; | ||
| import java.util.Collection; | ||
| import java.util.Collections; | ||
| import java.util.List; | ||
| import java.util.Objects; | ||
| import java.util.Set; | ||
| import java.util.stream.Collectors; | ||
| import org.apache.hadoop.conf.Configurable; | ||
| import org.apache.hadoop.conf.Configuration; | ||
| import org.apache.hadoop.hbase.master.RegionPlan; | ||
| import org.apache.hadoop.hbase.util.ReflectionUtils; | ||
| import org.apache.yetus.audience.InterfaceAudience; | ||
| import org.slf4j.Logger; | ||
| import org.slf4j.LoggerFactory; | ||
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| import org.apache.hbase.thirdparty.com.google.common.collect.ImmutableSet; | ||
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| /** | ||
| * Balancer conditionals supplement cost functions in the {@link StochasticLoadBalancer}. Cost | ||
| * functions are insufficient and difficult to work with when making discrete decisions; this is | ||
| * because they operate on a continuous scale, and each cost function's multiplier affects the | ||
| * relative importance of every other cost function. So it is difficult to meaningfully and clearly | ||
| * value many aspects of your region distribution via cost functions alone. Conditionals allow you | ||
| * to very clearly define discrete rules that your balancer would ideally follow. To clarify, a | ||
| * conditional violation will not block a region assignment because we would prefer to have uptime | ||
| * than have perfectly intentional balance. But conditionals allow you to, for example, define that | ||
| * a region's primary and secondary should not live on the same rack. Another example, conditionals | ||
| * make it easy to define that system tables will ideally be isolated on their own RegionServer | ||
| * (without needing to manage distinct RegionServer groups). Use of conditionals may cause an | ||
| * extremely unbalanced cluster to exceed its max balancer runtime. This is necessary because | ||
| * conditional candidate generation is quite expensive, and cutting it off early could prevent us | ||
| * from finding a solution. | ||
| */ | ||
| @InterfaceAudience.Private | ||
| final class BalancerConditionals implements Configurable { | ||
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| private static final Logger LOG = LoggerFactory.getLogger(BalancerConditionals.class); | ||
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| static final BalancerConditionals INSTANCE = new BalancerConditionals(); | ||
| public static final String DISTRIBUTE_REPLICAS_KEY = | ||
| "hbase.master.balancer.stochastic.conditionals.distributeReplicas"; | ||
| public static final boolean DISTRIBUTE_REPLICAS_DEFAULT = false; | ||
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| public static final String ADDITIONAL_CONDITIONALS_KEY = | ||
| "hbase.master.balancer.stochastic.additionalConditionals"; | ||
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| private Set<Class<? extends RegionPlanConditional>> conditionalClasses = Collections.emptySet(); | ||
| private Set<RegionPlanConditional> conditionals = Collections.emptySet(); | ||
| private Configuration conf; | ||
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| private BalancerConditionals() { | ||
| } | ||
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| boolean shouldRunBalancer(BalancerClusterState cluster) { | ||
| return isConditionalBalancingEnabled() && conditionals.stream() | ||
| .map(RegionPlanConditional::getCandidateGenerators).flatMap(Collection::stream) | ||
| .map(generator -> generator.getWeight(cluster)).anyMatch(weight -> weight > 0); | ||
| } | ||
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| Set<Class<? extends RegionPlanConditional>> getConditionalClasses() { | ||
| return Set.copyOf(conditionalClasses); | ||
| } | ||
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| Collection<RegionPlanConditional> getConditionals() { | ||
| return conditionals; | ||
| } | ||
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| boolean isReplicaDistributionEnabled() { | ||
| return conditionalClasses.contains(DistributeReplicasConditional.class); | ||
| } | ||
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| boolean shouldSkipSloppyServerEvaluation() { | ||
| return isConditionalBalancingEnabled(); | ||
| } | ||
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| boolean isConditionalBalancingEnabled() { | ||
| return !conditionalClasses.isEmpty(); | ||
| } | ||
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| void clearConditionalWeightCaches() { | ||
| conditionals.stream().map(RegionPlanConditional::getCandidateGenerators) | ||
| .flatMap(Collection::stream) | ||
| .forEach(RegionPlanConditionalCandidateGenerator::clearWeightCache); | ||
| } | ||
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| void loadClusterState(BalancerClusterState cluster) { | ||
| conditionals = conditionalClasses.stream().map(clazz -> createConditional(clazz, conf, cluster)) | ||
| .filter(Objects::nonNull).collect(Collectors.toSet()); | ||
| } | ||
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| /** | ||
| * Indicates whether the action is good for our conditional compliance. | ||
| * @param cluster The cluster state | ||
| * @param action The proposed action | ||
| * @return -1 if conditionals improve, 0 if neutral, 1 if conditionals degrade | ||
| */ | ||
| int getViolationCountChange(BalancerClusterState cluster, BalanceAction action) { | ||
| boolean isViolatingPre = isViolating(cluster, action.undoAction()); | ||
| boolean isViolatingPost = isViolating(cluster, action); | ||
| if (isViolatingPre && isViolatingPost) { | ||
| return 0; | ||
| } else if (!isViolatingPre && isViolatingPost) { | ||
| return 1; | ||
| } else { | ||
| return -1; | ||
| } | ||
| } | ||
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| /** | ||
| * Check if the proposed action violates conditionals | ||
| * @param cluster The cluster state | ||
| * @param action The proposed action | ||
| */ | ||
| boolean isViolating(BalancerClusterState cluster, BalanceAction action) { | ||
| conditionals.forEach(conditional -> conditional.refreshClusterState(cluster)); | ||
| if (conditionals.isEmpty()) { | ||
| return false; | ||
| } | ||
| List<RegionPlan> regionPlans = cluster.convertActionToPlans(action); | ||
| for (RegionPlan regionPlan : regionPlans) { | ||
| if (isViolating(regionPlan)) { | ||
| return true; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
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| private boolean isViolating(RegionPlan regionPlan) { | ||
| for (RegionPlanConditional conditional : conditionals) { | ||
| if (conditional.isViolating(regionPlan)) { | ||
| return true; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
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| private RegionPlanConditional createConditional(Class<? extends RegionPlanConditional> clazz, | ||
| Configuration conf, BalancerClusterState cluster) { | ||
| if (conf == null) { | ||
| conf = new Configuration(); | ||
| } | ||
| if (cluster == null) { | ||
| cluster = new BalancerClusterState(Collections.emptyMap(), null, null, null, null); | ||
| } | ||
| try { | ||
| Constructor<? extends RegionPlanConditional> ctor = | ||
| clazz.getDeclaredConstructor(Configuration.class, BalancerClusterState.class); | ||
| return ReflectionUtils.instantiate(clazz.getName(), ctor, conf, cluster); | ||
| } catch (NoSuchMethodException e) { | ||
| LOG.warn("Cannot find constructor with Configuration and " | ||
| + "BalancerClusterState parameters for class '{}': {}", clazz.getName(), e.getMessage()); | ||
| } | ||
| return null; | ||
| } | ||
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| @Override | ||
| public void setConf(Configuration conf) { | ||
| this.conf = conf; | ||
| ImmutableSet.Builder<Class<? extends RegionPlanConditional>> conditionalClasses = | ||
| ImmutableSet.builder(); | ||
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| boolean distributeReplicas = | ||
| conf.getBoolean(DISTRIBUTE_REPLICAS_KEY, DISTRIBUTE_REPLICAS_DEFAULT); | ||
| if (distributeReplicas) { | ||
| conditionalClasses.add(DistributeReplicasConditional.class); | ||
| } | ||
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| Class<?>[] classes = conf.getClasses(ADDITIONAL_CONDITIONALS_KEY); | ||
| for (Class<?> clazz : classes) { | ||
| if (!RegionPlanConditional.class.isAssignableFrom(clazz)) { | ||
| LOG.warn("Class {} is not a RegionPlanConditional", clazz.getName()); | ||
| continue; | ||
| } | ||
| conditionalClasses.add(clazz.asSubclass(RegionPlanConditional.class)); | ||
| } | ||
| this.conditionalClasses = conditionalClasses.build(); | ||
| loadClusterState(null); | ||
| } | ||
|
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| @Override | ||
| public Configuration getConf() { | ||
| return conf; | ||
| } | ||
| } |
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