cmccabe commented on a change in pull request #10494: URL: https://github.com/apache/kafka/pull/10494#discussion_r632796424
########## File path: metadata/src/main/java/org/apache/kafka/controller/StripedReplicaPlacer.java ########## @@ -0,0 +1,411 @@ +/* + * 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.kafka.controller; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.Iterator; +import java.util.List; +import java.util.Map; +import java.util.Optional; +import java.util.Random; + +import org.apache.kafka.common.errors.InvalidReplicationFactorException; +import org.apache.kafka.metadata.OptionalStringComparator; +import org.apache.kafka.metadata.UsableBroker; + + +/** + * The striped replica placer. + * + * + * GOALS + * The design of this placer attempts to satisfy a few competing goals. Firstly, we want + * to spread the replicas as evenly as we can across racks. In the simple case where + * broker racks have not been configured, this goal is a no-op, of course. But it is the + * highest priority goal in multi-rack clusters. + * + * Our second goal is to spread the replicas evenly across brokers. Since we are placing + * multiple partitions, we try to avoid putting each partition on the same set of + * replicas, even if it does satisfy the rack placement goal. However, we treat the rack + * placement goal as higher priority than this goal-- if you configure 10 brokers in rack + * A and B, and 1 broker in rack C, you will end up with a lot of partitions on that one + * broker in rack C. If you were to place a lot of partitions with replication factor 3, + * each partition would try to get a replica there. In general racks are supposed to be + * about the same size -- if they aren't, this is a user error. + * + * Thirdly, we would prefer to place replicas on unfenced brokers, rather than on fenced Review comment: I added some text saying that we want new leaders to be evenly distributed if any one broker is fenced -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
