ndimiduk commented on code in PR #6651: URL: https://github.com/apache/hbase/pull/6651#discussion_r1965211358
########## hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/BalancerConditionals.java: ########## @@ -0,0 +1,212 @@ +/* + * 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; + +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.master.balancer.replicas.ReplicaKeyCache; +import org.apache.hadoop.hbase.util.ReflectionUtils; +import org.apache.yetus.audience.InterfaceAudience; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import org.apache.hbase.thirdparty.com.google.common.collect.ImmutableSet; + +/** + * 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). + */ [email protected] +final class BalancerConditionals implements Configurable { + + private static final Logger LOG = LoggerFactory.getLogger(BalancerConditionals.class); + + public static final String DISTRIBUTE_REPLICAS_KEY = + "hbase.master.balancer.stochastic.conditionals.distributeReplicas"; + public static final boolean DISTRIBUTE_REPLICAS_DEFAULT = false; + + public static final String ADDITIONAL_CONDITIONALS_KEY = + "hbase.master.balancer.stochastic.additionalConditionals"; + + private Set<Class<? extends RegionPlanConditional>> conditionalClasses = Collections.emptySet(); + private Set<RegionPlanConditional> conditionals = Collections.emptySet(); + private Configuration conf; + + static BalancerConditionals create() { + return new BalancerConditionals(); + } + + private BalancerConditionals() { + } + + boolean shouldRunBalancer(BalancerClusterState cluster) { + return isConditionalBalancingEnabled() && conditionals.stream() + .map(RegionPlanConditional::getCandidateGenerators).flatMap(Collection::stream) + .map(generator -> generator.getWeight(cluster)).anyMatch(weight -> weight > 0); + } + + Set<Class<? extends RegionPlanConditional>> getConditionalClasses() { + return Set.copyOf(conditionalClasses); + } + + Collection<RegionPlanConditional> getConditionals() { + return conditionals; + } + + boolean isReplicaDistributionEnabled() { + return conditionalClasses.stream() + .anyMatch(DistributeReplicasConditional.class::isAssignableFrom); + } + + boolean shouldSkipSloppyServerEvaluation() { + return isConditionalBalancingEnabled(); + } + + boolean isConditionalBalancingEnabled() { + return !conditionalClasses.isEmpty(); + } + + void clearConditionalWeightCaches() { + conditionals.stream().map(RegionPlanConditional::getCandidateGenerators) + .flatMap(Collection::stream) + .forEach(RegionPlanConditionalCandidateGenerator::clearWeightCache); + } + + void loadClusterState(BalancerClusterState cluster) { + conditionals = conditionalClasses.stream().map(clazz -> createConditional(clazz, cluster)) + .filter(Objects::nonNull).collect(Collectors.toSet()); + } + + /** + * 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) { + // Cluster is in pre-move state, so figure out the proposed violations + boolean isViolatingPost = isViolating(cluster, action); + cluster.doAction(action); + + // Cluster is in post-move state, so figure out the original violations + BalanceAction undoAction = action.undoAction(); + boolean isViolatingPre = isViolating(cluster, undoAction); + + // Reset cluster + cluster.doAction(undoAction); + + if (isViolatingPre && isViolatingPost) { Review Comment: This looks a lot like a `Comparator`. -- This is an automated message from the Apache Git Service. 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