kirktrue commented on code in PR #14357: URL: https://github.com/apache/kafka/pull/14357#discussion_r1353534627
########## clients/src/main/java/org/apache/kafka/clients/consumer/internals/AssignmentReconciler.java: ########## @@ -0,0 +1,355 @@ +/* + * 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.clients.consumer.internals; + +import org.apache.kafka.clients.consumer.ConsumerRebalanceListener; +import org.apache.kafka.clients.consumer.internals.events.AssignPartitionsEvent; +import org.apache.kafka.clients.consumer.internals.events.BackgroundEvent; +import org.apache.kafka.clients.consumer.internals.events.LosePartitionsEvent; +import org.apache.kafka.clients.consumer.internals.events.RebalanceCallbackEvent; +import org.apache.kafka.clients.consumer.internals.events.RevokePartitionsEvent; +import org.apache.kafka.common.TopicPartition; +import org.apache.kafka.common.Uuid; +import org.apache.kafka.common.message.ConsumerGroupHeartbeatResponseData.Assignment; +import org.apache.kafka.common.message.ConsumerGroupHeartbeatResponseData.TopicPartitions; +import org.apache.kafka.clients.consumer.internals.Utils.TopicPartitionComparator; +import org.apache.kafka.common.utils.LogContext; +import org.slf4j.Logger; + +import java.util.Collection; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.Map; +import java.util.Objects; +import java.util.Optional; +import java.util.Set; +import java.util.SortedSet; +import java.util.TreeSet; +import java.util.concurrent.BlockingQueue; +import java.util.stream.Collectors; + +/** + * {@code AssignmentReconciler} performs the work of reconciling this consumer's partition assignment as directed + * by the consumer group coordinator. When the coordinator determines that a change to the partition ownership of + * the group is required, it will communicate with each consumer to relay its respective <em>target</em> + * assignment, that is, the set of partitions for which that consumer should now assume ownership. It is the then the + * responsibility of the consumer to work toward that target by performing the necessary internal modifications to + * satisfy the assignment from the coordinator. In practical terms, this means that it must first determine the set + * difference between the <em>{@link SubscriptionState#assignedPartitions() current assignment}</em> and the + * <em>{@link Assignment#assignedTopicPartitions() target assignment}</em>. + * + * <p/> + * + * Internally, reconciliation is a multi-step process: + * + * <ol> + * <li>Calculating partitions to revoke</li> + * <li>Invoking {@link ConsumerRebalanceListener#onPartitionsRevoked(Collection)}</li> + * <li>Removing those partitions from its {@link SubscriptionState#assignFromSubscribed(Collection) assignment}</li> + * <li>Perform a heartbeat acknowledgement with the group coordinator</li> + * <li>Calculating partitions to assign</li> + * <li>Invoking {@link ConsumerRebalanceListener#onPartitionsAssigned(Collection)}</li> + * <li>Adding those partitions to its {@link SubscriptionState#assignFromSubscribed(Collection) assignment}</li> + * <li>Perform a heartbeat acknowledgement with the group coordinator</li> + * </ol> + * + * <p/> + * + * Because the target assignment from the group coordinator is <em>declarative</em>, the implementation of the + * reconciliation process is idempotent. The caller of this class is free to invoke {@link #maybeReconcile(Optional)} + * repeatedly for as long as the group coordinator provides an {@link Assignment}. + * + * <ul> + * <li> + * {@link ReconciliationResult#UNCHANGED}: no changes were made to the set of partitions. + * </li> + * <li> + * {@link ReconciliationResult#RECONCILING}: changes to the assignment have started. In practice this means + * that the appropriate {@link ConsumerRebalanceListener} callback method is being invoked. + * </li> + * <li> + * {@link ReconciliationResult#APPLIED_LOCALLY}: the {@link ConsumerRebalanceListener} callback method was made and + * the changes were applied locally. + * </li> + * </ul> + * + * The comparison against the {@link SubscriptionState#assignedPartitions() current set of assigned partitions} and + * the {@link Assignment#assignedTopicPartitions() target set of assigned partitions} is performed by essentially + * <em>flattening</em> the respective entries into two sets of {@link org.apache.kafka.common.TopicPartition partitons} + * which are then compared using basic {@link Set} comparisons. + */ +public class AssignmentReconciler { + + /** + * The result of the {@link #revoke(Optional)} or {@link #assign(Optional)} methods being invoked. + */ + enum ReconciliationResult { + UNCHANGED, + RECONCILING, + APPLIED_LOCALLY + } + + private final Logger log; + private final SubscriptionState subscriptions; + private final ConsumerMetadata metadata; + private final BlockingQueue<BackgroundEvent> backgroundEventQueue; + private Optional<RebalanceCallbackEvent> inflightCallback; + + AssignmentReconciler(LogContext logContext, + SubscriptionState subscriptions, + ConsumerMetadata metadata, + BlockingQueue<BackgroundEvent> backgroundEventQueue) { + this.log = logContext.logger(getClass()); + this.subscriptions = subscriptions; + this.metadata = metadata; + this.backgroundEventQueue = backgroundEventQueue; + } + + /** + * Perform the reconciliation process, as necessary to meet the given {@link Assignment target assignment}. Note + * that the reconciliation is a multi-step process, and this method should be invoked on each heartbeat if + * the coordinator provides a {@link Assignment target assignment}. + * + * @param assignment Target {@link Assignment} + * @return {@link ReconciliationResult} + */ + ReconciliationResult maybeReconcile(Optional<Assignment> assignment) { + // Check for any outstanding operations first. If a conclusive result has already been reached, return that + // before processing any further. + if (inflightCallback.isPresent()) { + // We don't actually need the _result_ of the event, just to know that it's complete. + if (inflightCallback.get().future().isDone()) { + // This is the happy path--we completed the callback. Clear out our inflight callback first, though. + inflightCallback = Optional.empty(); + return ReconciliationResult.APPLIED_LOCALLY; + } else { + // So we have a callback event out there, but it's neither complete nor expired, so wait. + return ReconciliationResult.RECONCILING; + } + } + + // First, we need to determine if any partitions need to be revoked. + switch (revoke(assignment)) { + case APPLIED_LOCALLY: + // If we've successfully revoked the partitions locally, we need to send an acknowledgement request + // ASAP to let the coordinator know. + log.debug("The revocation step of partition reconciliation has completed locally; will inform the consumer group coordinator"); + return ReconciliationResult.APPLIED_LOCALLY; + + case RECONCILING: + // At this point, we've started the revocation, but it isn't complete, so there's nothing + // to do here but wait until it's finished or expires. + log.debug("The revocation step of partition reconciliation is in progress"); + return ReconciliationResult.RECONCILING; + + case UNCHANGED: + log.debug("The revocation step of partition reconciliation has no changes; it was previously completed"); + break; + } + + // Next, we need to determine the partitions to be added, if any. + switch (assign(assignment)) { + case APPLIED_LOCALLY: + // If we've assigned one or more partitions, we need to send an acknowledgement request ASAP to + // let the coordinator know that they've been added locally. + log.debug("The assignment step of partition reconciliation has completed locally; will inform the consumer group coordinator"); + return ReconciliationResult.APPLIED_LOCALLY; + + case RECONCILING: + // At this point, we've started the assignment, but it isn't complete, so we wait... + log.debug("The assignment step of partition reconciliation is in progress"); + return ReconciliationResult.RECONCILING; + + case UNCHANGED: + log.debug("The assignment step of partition reconciliation has no changes; it was previously completed"); + break; + } + + log.debug("Both revocation and assignment steps of partition reconciliation are complete"); + return ReconciliationResult.UNCHANGED; + } + + ReconciliationResult lose() { + // Clear the inflight callback reference. This is done regardless of if one existed; if there was one it is + // now abandoned because we're going to "lose" our partitions. This will also allow us to skip the inflight + // check the other steps take. + inflightCallback = Optional.empty(); + + // For the lose step, our partition diff is simply all the partitions in our current assignment. + SetDifferenceGenerator setDifferenceGenerator = (assigned, target) -> sortPartitions(assigned); + + // For lose, we modify the "current" assignment by removing all its entries, full stop. We can thus ignore + // the diff-ed partitions that are passed in. + AssignmentGenerator assignmentGenerator = __ -> Collections.emptySortedSet(); + + return reconcile(Optional.empty(), + String.format("%s.onPartitionsLost()", ConsumerRebalanceListener.class.getSimpleName()), + setDifferenceGenerator, + LosePartitionsEvent::new, + assignmentGenerator); + } + + private ReconciliationResult revoke(Optional<Assignment> assignment) { + // For the revocation step, our partition diff is calculated by filtering out any partitions from our current + // assignment that aren't in the given target assignment. + SetDifferenceGenerator setDifferenceGenerator = (assigned, target) -> sortPartitions(assigned + .stream() + .filter(tp -> !target.contains(tp)) + .collect(Collectors.toSet())); + + // For revocation, we modify the "current" assignment by removing all entries that were not present in the + // "target" assignment. + AssignmentGenerator modifier = diffPartitions -> { + Set<TopicPartition> newAssignment = new HashSet<>(subscriptions.assignedPartitions()); + newAssignment.removeAll(diffPartitions); + return sortPartitions(newAssignment); + }; + + return reconcile(assignment, + String.format("%s.onPartitionsRevoked()", ConsumerRebalanceListener.class.getSimpleName()), + setDifferenceGenerator, + RevokePartitionsEvent::new, + modifier); + } + + private ReconciliationResult assign(Optional<Assignment> assignment) { + // For the assignment step, our partition diff is calculated by filtering out any partitions from the given + // target assignment that aren't presently in our current assignment. + SetDifferenceGenerator setDifferenceGenerator = (assigned, target) -> sortPartitions(target + .stream() + .filter(tp -> !assigned.contains(tp)) + .collect(Collectors.toSet())); + + // For assignment, we modify the "current" assignment by adding all entries that were present in the + // "target" assignment but not in the "current" assignment. + AssignmentGenerator modifier = diffPartitions -> { + Set<TopicPartition> newAssignment = new HashSet<>(subscriptions.assignedPartitions()); + newAssignment.addAll(diffPartitions); + return sortPartitions(newAssignment); + }; + + return reconcile(assignment, + String.format("%s.onPartitionsAssigned()", ConsumerRebalanceListener.class.getSimpleName()), + setDifferenceGenerator, + AssignPartitionsEvent::new, + modifier); + } + + private ReconciliationResult reconcile(Optional<Assignment> assignment, + String listenerMethodName, + SetDifferenceGenerator setDifferenceGenerator, + EventGenerator eventGenerator, + AssignmentGenerator assignmentGenerator) { + // "diff" the two sets of partitions: our "current" assignment and the "target" assignment. The result is + // sorted primarily so when the partitions show up in the logs, it's easier for us humans to understand. + SortedSet<TopicPartition> diffPartitions = setDifferenceGenerator.generate( + subscriptions.assignedPartitions(), + targetPartitions(metadata, assignment) + ); + + if (diffPartitions.isEmpty()) { + log.debug("Skipping invocation of {} as no partitions were changed in the new assignment", + listenerMethodName); + return ReconciliationResult.UNCHANGED; + } + + // Set up our callback invocation. We don't block here waiting on it its completion, though. + log.debug("Preparing to invoke {} with the following partitions: {}", listenerMethodName, diffPartitions); + RebalanceCallbackEvent event = eventGenerator.generate(diffPartitions); + inflightCallback = Optional.of(event); + + // Enqueue it in our background->application shared queue. This should be invoked in the Consumer.poll() method. + backgroundEventQueue.add(event); + + // It is only after the appropriate ConsumerRebalanceListener has been executed on the application thread + // (via Consumer.poll()), can we "commit" the change to the assigned partitions in SubscriptionState. + event.future().whenComplete((result, error) -> { + if (error != null) { + log.warn("An error occurred when invoking {} with the following partitions: {}", + listenerMethodName, + diffPartitions, + error); + // TODO: should we proceed or abort? + } + + log.debug("{} was successfully executed with the following partitions: {}", + listenerMethodName, + diffPartitions); + + SortedSet<TopicPartition> newAssignment = assignmentGenerator.generate(diffPartitions); + + // And finally... assign the new set of partitions! + subscriptions.assignFromSubscribed(newAssignment); Review Comment: Correct. -- This is an automated message from the Apache Git Service. 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