rreddy-22 commented on code in PR #13443: URL: https://github.com/apache/kafka/pull/13443#discussion_r1177156668
########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/RangeAssignor.java: ########## @@ -0,0 +1,261 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collection; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; + +import static java.lang.Math.min; + +/** + * The Server Side Sticky Range Assignor inherits properties of both the range assignor and the sticky assignor. + * Properties are as follows: + * <ol> + * <li> Each member must get at least one partition for every topic that it is subscribed to. The only exception is when + * the number of subscribed members is greater than the number of partitions for that topic. (Range) </li> + * <li> Partitions should be assigned to members in a way that facilitates the join operation when required. (Range) </li> + * This can only be done if every member is subscribed to the same topics and the topics are co-partitioned. + * Two streams are co-partitioned if the following conditions are met: + * <ul> + * <li> The keys must have the same schemas. + * <li> The topics involved must have the same number of partitions. + * </ul> + * <li> Members should retain as much of their previous assignment as possible to reduce the number of partition movements during reassignment. (Sticky) </li> + * </ol> + */ +public class RangeAssignor implements PartitionAssignor { + + private static final Logger log = LoggerFactory.getLogger(RangeAssignor.class); + + public static final String RANGE_ASSIGNOR_NAME = "range"; + + @Override + public String name() { + return RANGE_ASSIGNOR_NAME; + } + + static class RemainingAssignmentsForMember<String, Integer> { + private final String memberId; + private final Integer remaining; Review Comment: done ########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/RangeAssignor.java: ########## @@ -0,0 +1,261 @@ +/* + * 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.coordinator.group.assignor; + +import org.apache.kafka.common.Uuid; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.ArrayList; +import java.util.Collection; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; + +import static java.lang.Math.min; + +/** + * The Server Side Sticky Range Assignor inherits properties of both the range assignor and the sticky assignor. + * Properties are as follows: + * <ol> + * <li> Each member must get at least one partition for every topic that it is subscribed to. The only exception is when + * the number of subscribed members is greater than the number of partitions for that topic. (Range) </li> + * <li> Partitions should be assigned to members in a way that facilitates the join operation when required. (Range) </li> + * This can only be done if every member is subscribed to the same topics and the topics are co-partitioned. + * Two streams are co-partitioned if the following conditions are met: + * <ul> + * <li> The keys must have the same schemas. + * <li> The topics involved must have the same number of partitions. + * </ul> + * <li> Members should retain as much of their previous assignment as possible to reduce the number of partition movements during reassignment. (Sticky) </li> + * </ol> + */ +public class RangeAssignor implements PartitionAssignor { + + private static final Logger log = LoggerFactory.getLogger(RangeAssignor.class); + + public static final String RANGE_ASSIGNOR_NAME = "range"; + + @Override + public String name() { + return RANGE_ASSIGNOR_NAME; + } + + static class RemainingAssignmentsForMember<String, Integer> { + private final String memberId; + private final Integer remaining; + + public RemainingAssignmentsForMember(String memberId, Integer remaining) { + this.memberId = memberId; + this.remaining = remaining; + } + + public String memberId() { + return memberId; + } + + public Integer remaining() { + return remaining; + } + + } + + private Map<Uuid, List<String>> membersPerTopic(final AssignmentSpec assignmentSpec) { + Map<Uuid, List<String>> membersPerTopic = new HashMap<>(); + Map<String, AssignmentMemberSpec> membersData = assignmentSpec.members(); + + membersData.forEach((memberId, memberMetadata) -> { + Collection<Uuid> topics = memberMetadata.subscribedTopicIds(); + for (Uuid topicId: topics) { + // Only topics that are present in both the subscribed topics list and the topic metadata should be considered for assignment. + if (assignmentSpec.topics().containsKey(topicId)) { + membersPerTopic + .computeIfAbsent(topicId, k -> new ArrayList<>()) + .add(memberId); + } else { + log.warn(memberId + " subscribed to topic " + topicId + " which doesn't exist in the topic metadata"); + } + } + }); + + return membersPerTopic; + } + + private Map<Uuid, List<Integer>> getUnassignedPartitionsPerTopic(final AssignmentSpec assignmentSpec, Map<Uuid, Set<Integer>> assignedStickyPartitionsPerTopic) { + Map<Uuid, List<Integer>> unassignedPartitionsPerTopic = new HashMap<>(); + Map<Uuid, AssignmentTopicMetadata> topicsMetadata = assignmentSpec.topics(); + + topicsMetadata.forEach((topicId, assignmentTopicMetadata) -> { + ArrayList<Integer> unassignedPartitionsForTopic = new ArrayList<>(); + int numPartitions = assignmentTopicMetadata.numPartitions(); + // List of unassigned partitions per topic contains the partitions in ascending order. + Set<Integer> assignedStickyPartitionsForTopic = assignedStickyPartitionsPerTopic.getOrDefault(topicId, new HashSet<>()); + for (int i = 0; i < numPartitions; i++) { + if (!assignedStickyPartitionsForTopic.contains(i)) { + unassignedPartitionsForTopic.add(i); + } + } + unassignedPartitionsPerTopic.put(topicId, unassignedPartitionsForTopic); + }); + + return unassignedPartitionsPerTopic; + } + +/** + * <p> The algorithm includes the following steps: + * <ol> + * <li> Generate a map of <code>membersPerTopic</code> using the given member subscriptions.</li> + * <li> Generate a list of members (<code>potentiallyUnfilledMembers</code>) that have not met the minimum required quota for assignment AND + * get a list (<code>assignedStickyPartitionsPerTopic</code>) of partitions that we want to retain in the new assignment.</li> + * <li> Add members from the <code>potentiallyUnfilledMembers</code> list to the <code>unfilledMembers</code> list if they haven't met the total required quota i.e. minimum number of partitions per member + 1 (if member is designated to receive one of the excess partitions). </li> + * <li> Generate a list of unassigned partitions by calculating the difference between total partitions and already assigned (sticky) partitions. </li> + * <li> Iterate through the unfilled members and assign partitions from the unassigned partitions. </li> + * </ol> + * </p> + */ + @Override + public GroupAssignment assign(final AssignmentSpec assignmentSpec) throws PartitionAssignorException { + Map<String, Map<Uuid, Set<Integer>>> membersWithNewAssignmentPerTopic = new HashMap<>(); + // Step 1 + Map<Uuid, List<String>> membersPerTopic = membersPerTopic(assignmentSpec); + // Step 2 + Map<Uuid, List<RemainingAssignmentsForMember<String, Integer>>> unfilledMembersPerTopic = new HashMap<>(); + Map<Uuid, Set<Integer>> assignedStickyPartitionsPerTopic = new HashMap<>(); + + membersPerTopic.forEach((topicId, membersForTopic) -> { + // For each topic we have a temporary list of members stored in potentiallyUnfilledMembers. + // The list is populated with members that satisfy one of the two conditions: + // 1) Members that already have the minimum required number of partitions i.e. total partitions divided by total subscribed members + // BUT they could be assigned an extra partition later on. Extra partitions exist if total partitions % number of members is greater than 0. + // In this case we add the member to the unfilled members map iff an extra partition needs to be assigned to it. + // 2) Members that don't have the minimum required partitions, so irrespective of whether they get an extra partition or not they get added to the unfilled map later. + List<RemainingAssignmentsForMember<String, Integer>> potentiallyUnfilledMembers = new ArrayList<>(); + + AssignmentTopicMetadata topicData = assignmentSpec.topics().get(topicId); + int numPartitionsForTopic = topicData.numPartitions(); + + // Idle members case : When the number of members subscribed to a topic is greater than the total number of partitions, + // all members get assigned via the "extra partitions" logic since minRequiredQuota = 0. + int minRequiredQuota = numPartitionsForTopic / membersForTopic.size(); + // Each member can get only ONE extra partition per topic after receiving the minimum quota. + int numMembersWithExtraPartition = numPartitionsForTopic % membersForTopic.size(); + + for (String memberId: membersForTopic) { + Set<Integer> assignedPartitionsForTopic = assignmentSpec.members().get(memberId) + .assignedPartitions().getOrDefault(topicId, Collections.emptySet()); + + int currentAssignmentSize = assignedPartitionsForTopic.size(); + List<Integer> currentAssignmentListForTopic = new ArrayList<>(assignedPartitionsForTopic); + + // If there were previously assigned partitions present, we want to retain them. + if (currentAssignmentSize > 0) { + // We need to retain: + // 1) currentSize number of partitions (when currentSize < required) OR + // 2) required number of partitions (when currentSize > required). + int retainedPartitionsCount = min(currentAssignmentSize, minRequiredQuota); + // The partitions need to be in ascending order since we want the same partition numbers from each topic + // to go to the same member to facilitate joins in case of co-partitioned topics. + Collections.sort(currentAssignmentListForTopic); + for (int i = 0; i < retainedPartitionsCount; i++) { + assignedStickyPartitionsPerTopic + .computeIfAbsent(topicId, k -> new HashSet<>()) + .add(currentAssignmentListForTopic.get(i)); + membersWithNewAssignmentPerTopic + .computeIfAbsent(memberId, k -> new HashMap<>()) + .computeIfAbsent(topicId, k -> new HashSet<>()) + .add(currentAssignmentListForTopic.get(i)); + } + } + + // Number of partitions left to reach the minRequiredQuota. + int remaining = minRequiredQuota - currentAssignmentSize; + + // There are 3 cases w.r.t the value of remaining: + // 1) remaining < 0: this means that the member has more than the min required amount. + if (remaining < 0 && numMembersWithExtraPartition > 0) { + // In order to remain as sticky as possible, since the order of members can be different, we want the members that already had extra + // partitions to retain them if it's still required, instead of assigning the extras to the first few members directly. + numMembersWithExtraPartition--; + // Since we already added the minimumRequiredQuota of partitions in the previous step (until minReq - 1), we just need to + // add the extra partition that will be present at the index right after min quota was satisfied. + assignedStickyPartitionsPerTopic + .computeIfAbsent(topicId, k -> new HashSet<>()) + .add(currentAssignmentListForTopic.get(minRequiredQuota)); + membersWithNewAssignmentPerTopic + .computeIfAbsent(memberId, k -> new HashMap<>()) + .computeIfAbsent(topicId, k -> new HashSet<>()) + .add(currentAssignmentListForTopic.get(minRequiredQuota)); + } else { + // 2) If remaining = 0: it has min req partitions but there is scope for getting an extra partition later on, so it is a potential unfilled member. Review Comment: I think they're the same thing tbh :( -- 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. To unsubscribe, e-mail: jira-unsubscr...@kafka.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
