| package sarama |
| |
| import ( |
| "container/heap" |
| "errors" |
| "fmt" |
| "math" |
| "sort" |
| "strings" |
| ) |
| |
| const ( |
| // RangeBalanceStrategyName identifies strategies that use the range partition assignment strategy |
| RangeBalanceStrategyName = "range" |
| |
| // RoundRobinBalanceStrategyName identifies strategies that use the round-robin partition assignment strategy |
| RoundRobinBalanceStrategyName = "roundrobin" |
| |
| // StickyBalanceStrategyName identifies strategies that use the sticky-partition assignment strategy |
| StickyBalanceStrategyName = "sticky" |
| |
| defaultGeneration = -1 |
| ) |
| |
| // BalanceStrategyPlan is the results of any BalanceStrategy.Plan attempt. |
| // It contains an allocation of topic/partitions by memberID in the form of |
| // a `memberID -> topic -> partitions` map. |
| type BalanceStrategyPlan map[string]map[string][]int32 |
| |
| // Add assigns a topic with a number partitions to a member. |
| func (p BalanceStrategyPlan) Add(memberID, topic string, partitions ...int32) { |
| if len(partitions) == 0 { |
| return |
| } |
| if _, ok := p[memberID]; !ok { |
| p[memberID] = make(map[string][]int32, 1) |
| } |
| p[memberID][topic] = append(p[memberID][topic], partitions...) |
| } |
| |
| // -------------------------------------------------------------------- |
| |
| // BalanceStrategy is used to balance topics and partitions |
| // across members of a consumer group |
| type BalanceStrategy interface { |
| // Name uniquely identifies the strategy. |
| Name() string |
| |
| // Plan accepts a map of `memberID -> metadata` and a map of `topic -> partitions` |
| // and returns a distribution plan. |
| Plan(members map[string]ConsumerGroupMemberMetadata, topics map[string][]int32) (BalanceStrategyPlan, error) |
| |
| // AssignmentData returns the serialized assignment data for the specified |
| // memberID |
| AssignmentData(memberID string, topics map[string][]int32, generationID int32) ([]byte, error) |
| } |
| |
| // -------------------------------------------------------------------- |
| |
| // BalanceStrategyRange is the default and assigns partitions as ranges to consumer group members. |
| // Example with one topic T with six partitions (0..5) and two members (M1, M2): |
| // M1: {T: [0, 1, 2]} |
| // M2: {T: [3, 4, 5]} |
| var BalanceStrategyRange = &balanceStrategy{ |
| name: RangeBalanceStrategyName, |
| coreFn: func(plan BalanceStrategyPlan, memberIDs []string, topic string, partitions []int32) { |
| step := float64(len(partitions)) / float64(len(memberIDs)) |
| |
| for i, memberID := range memberIDs { |
| pos := float64(i) |
| min := int(math.Floor(pos*step + 0.5)) |
| max := int(math.Floor((pos+1)*step + 0.5)) |
| plan.Add(memberID, topic, partitions[min:max]...) |
| } |
| }, |
| } |
| |
| // BalanceStrategySticky assigns partitions to members with an attempt to preserve earlier assignments |
| // while maintain a balanced partition distribution. |
| // Example with topic T with six partitions (0..5) and two members (M1, M2): |
| // M1: {T: [0, 2, 4]} |
| // M2: {T: [1, 3, 5]} |
| // |
| // On reassignment with an additional consumer, you might get an assignment plan like: |
| // M1: {T: [0, 2]} |
| // M2: {T: [1, 3]} |
| // M3: {T: [4, 5]} |
| // |
| var BalanceStrategySticky = &stickyBalanceStrategy{} |
| |
| // -------------------------------------------------------------------- |
| |
| type balanceStrategy struct { |
| name string |
| coreFn func(plan BalanceStrategyPlan, memberIDs []string, topic string, partitions []int32) |
| } |
| |
| // Name implements BalanceStrategy. |
| func (s *balanceStrategy) Name() string { return s.name } |
| |
| // Plan implements BalanceStrategy. |
| func (s *balanceStrategy) Plan(members map[string]ConsumerGroupMemberMetadata, topics map[string][]int32) (BalanceStrategyPlan, error) { |
| // Build members by topic map |
| mbt := make(map[string][]string) |
| for memberID, meta := range members { |
| for _, topic := range meta.Topics { |
| mbt[topic] = append(mbt[topic], memberID) |
| } |
| } |
| |
| // Sort members for each topic |
| for topic, memberIDs := range mbt { |
| sort.Sort(&balanceStrategySortable{ |
| topic: topic, |
| memberIDs: memberIDs, |
| }) |
| } |
| |
| // Assemble plan |
| plan := make(BalanceStrategyPlan, len(members)) |
| for topic, memberIDs := range mbt { |
| s.coreFn(plan, memberIDs, topic, topics[topic]) |
| } |
| return plan, nil |
| } |
| |
| // AssignmentData simple strategies do not require any shared assignment data |
| func (s *balanceStrategy) AssignmentData(memberID string, topics map[string][]int32, generationID int32) ([]byte, error) { |
| return nil, nil |
| } |
| |
| type balanceStrategySortable struct { |
| topic string |
| memberIDs []string |
| } |
| |
| func (p balanceStrategySortable) Len() int { return len(p.memberIDs) } |
| func (p balanceStrategySortable) Swap(i, j int) { |
| p.memberIDs[i], p.memberIDs[j] = p.memberIDs[j], p.memberIDs[i] |
| } |
| |
| func (p balanceStrategySortable) Less(i, j int) bool { |
| return balanceStrategyHashValue(p.topic, p.memberIDs[i]) < balanceStrategyHashValue(p.topic, p.memberIDs[j]) |
| } |
| |
| func balanceStrategyHashValue(vv ...string) uint32 { |
| h := uint32(2166136261) |
| for _, s := range vv { |
| for _, c := range s { |
| h ^= uint32(c) |
| h *= 16777619 |
| } |
| } |
| return h |
| } |
| |
| type stickyBalanceStrategy struct { |
| movements partitionMovements |
| } |
| |
| // Name implements BalanceStrategy. |
| func (s *stickyBalanceStrategy) Name() string { return StickyBalanceStrategyName } |
| |
| // Plan implements BalanceStrategy. |
| func (s *stickyBalanceStrategy) Plan(members map[string]ConsumerGroupMemberMetadata, topics map[string][]int32) (BalanceStrategyPlan, error) { |
| // track partition movements during generation of the partition assignment plan |
| s.movements = partitionMovements{ |
| Movements: make(map[topicPartitionAssignment]consumerPair), |
| PartitionMovementsByTopic: make(map[string]map[consumerPair]map[topicPartitionAssignment]bool), |
| } |
| |
| // prepopulate the current assignment state from userdata on the consumer group members |
| currentAssignment, prevAssignment, err := prepopulateCurrentAssignments(members) |
| if err != nil { |
| return nil, err |
| } |
| |
| // determine if we're dealing with a completely fresh assignment, or if there's existing assignment state |
| isFreshAssignment := false |
| if len(currentAssignment) == 0 { |
| isFreshAssignment = true |
| } |
| |
| // create a mapping of all current topic partitions and the consumers that can be assigned to them |
| partition2AllPotentialConsumers := make(map[topicPartitionAssignment][]string) |
| for topic, partitions := range topics { |
| for _, partition := range partitions { |
| partition2AllPotentialConsumers[topicPartitionAssignment{Topic: topic, Partition: partition}] = []string{} |
| } |
| } |
| |
| // create a mapping of all consumers to all potential topic partitions that can be assigned to them |
| // also, populate the mapping of partitions to potential consumers |
| consumer2AllPotentialPartitions := make(map[string][]topicPartitionAssignment, len(members)) |
| for memberID, meta := range members { |
| consumer2AllPotentialPartitions[memberID] = make([]topicPartitionAssignment, 0) |
| for _, topicSubscription := range meta.Topics { |
| // only evaluate topic subscriptions that are present in the supplied topics map |
| if _, found := topics[topicSubscription]; found { |
| for _, partition := range topics[topicSubscription] { |
| topicPartition := topicPartitionAssignment{Topic: topicSubscription, Partition: partition} |
| consumer2AllPotentialPartitions[memberID] = append(consumer2AllPotentialPartitions[memberID], topicPartition) |
| partition2AllPotentialConsumers[topicPartition] = append(partition2AllPotentialConsumers[topicPartition], memberID) |
| } |
| } |
| } |
| |
| // add this consumer to currentAssignment (with an empty topic partition assignment) if it does not already exist |
| if _, exists := currentAssignment[memberID]; !exists { |
| currentAssignment[memberID] = make([]topicPartitionAssignment, 0) |
| } |
| } |
| |
| // create a mapping of each partition to its current consumer, where possible |
| currentPartitionConsumers := make(map[topicPartitionAssignment]string, len(currentAssignment)) |
| unvisitedPartitions := make(map[topicPartitionAssignment]bool, len(partition2AllPotentialConsumers)) |
| for partition := range partition2AllPotentialConsumers { |
| unvisitedPartitions[partition] = true |
| } |
| var unassignedPartitions []topicPartitionAssignment |
| for memberID, partitions := range currentAssignment { |
| var keepPartitions []topicPartitionAssignment |
| for _, partition := range partitions { |
| // If this partition no longer exists at all, likely due to the |
| // topic being deleted, we remove the partition from the member. |
| if _, exists := partition2AllPotentialConsumers[partition]; !exists { |
| continue |
| } |
| delete(unvisitedPartitions, partition) |
| currentPartitionConsumers[partition] = memberID |
| |
| if !strsContains(members[memberID].Topics, partition.Topic) { |
| unassignedPartitions = append(unassignedPartitions, partition) |
| continue |
| } |
| keepPartitions = append(keepPartitions, partition) |
| } |
| currentAssignment[memberID] = keepPartitions |
| } |
| for unvisited := range unvisitedPartitions { |
| unassignedPartitions = append(unassignedPartitions, unvisited) |
| } |
| |
| // sort the topic partitions in order of priority for reassignment |
| sortedPartitions := sortPartitions(currentAssignment, prevAssignment, isFreshAssignment, partition2AllPotentialConsumers, consumer2AllPotentialPartitions) |
| |
| // at this point we have preserved all valid topic partition to consumer assignments and removed |
| // all invalid topic partitions and invalid consumers. Now we need to assign unassignedPartitions |
| // to consumers so that the topic partition assignments are as balanced as possible. |
| |
| // an ascending sorted set of consumers based on how many topic partitions are already assigned to them |
| sortedCurrentSubscriptions := sortMemberIDsByPartitionAssignments(currentAssignment) |
| s.balance(currentAssignment, prevAssignment, sortedPartitions, unassignedPartitions, sortedCurrentSubscriptions, consumer2AllPotentialPartitions, partition2AllPotentialConsumers, currentPartitionConsumers) |
| |
| // Assemble plan |
| plan := make(BalanceStrategyPlan, len(currentAssignment)) |
| for memberID, assignments := range currentAssignment { |
| if len(assignments) == 0 { |
| plan[memberID] = make(map[string][]int32) |
| } else { |
| for _, assignment := range assignments { |
| plan.Add(memberID, assignment.Topic, assignment.Partition) |
| } |
| } |
| } |
| return plan, nil |
| } |
| |
| // AssignmentData serializes the set of topics currently assigned to the |
| // specified member as part of the supplied balance plan |
| func (s *stickyBalanceStrategy) AssignmentData(memberID string, topics map[string][]int32, generationID int32) ([]byte, error) { |
| return encode(&StickyAssignorUserDataV1{ |
| Topics: topics, |
| Generation: generationID, |
| }, nil) |
| } |
| |
| func strsContains(s []string, value string) bool { |
| for _, entry := range s { |
| if entry == value { |
| return true |
| } |
| } |
| return false |
| } |
| |
| // Balance assignments across consumers for maximum fairness and stickiness. |
| func (s *stickyBalanceStrategy) balance(currentAssignment map[string][]topicPartitionAssignment, prevAssignment map[topicPartitionAssignment]consumerGenerationPair, sortedPartitions []topicPartitionAssignment, unassignedPartitions []topicPartitionAssignment, sortedCurrentSubscriptions []string, consumer2AllPotentialPartitions map[string][]topicPartitionAssignment, partition2AllPotentialConsumers map[topicPartitionAssignment][]string, currentPartitionConsumer map[topicPartitionAssignment]string) { |
| initializing := false |
| if len(sortedCurrentSubscriptions) == 0 || len(currentAssignment[sortedCurrentSubscriptions[0]]) == 0 { |
| initializing = true |
| } |
| |
| // assign all unassigned partitions |
| for _, partition := range unassignedPartitions { |
| // skip if there is no potential consumer for the partition |
| if len(partition2AllPotentialConsumers[partition]) == 0 { |
| continue |
| } |
| sortedCurrentSubscriptions = assignPartition(partition, sortedCurrentSubscriptions, currentAssignment, consumer2AllPotentialPartitions, currentPartitionConsumer) |
| } |
| |
| // narrow down the reassignment scope to only those partitions that can actually be reassigned |
| for partition := range partition2AllPotentialConsumers { |
| if !canTopicPartitionParticipateInReassignment(partition, partition2AllPotentialConsumers) { |
| sortedPartitions = removeTopicPartitionFromMemberAssignments(sortedPartitions, partition) |
| } |
| } |
| |
| // narrow down the reassignment scope to only those consumers that are subject to reassignment |
| fixedAssignments := make(map[string][]topicPartitionAssignment) |
| for memberID := range consumer2AllPotentialPartitions { |
| if !canConsumerParticipateInReassignment(memberID, currentAssignment, consumer2AllPotentialPartitions, partition2AllPotentialConsumers) { |
| fixedAssignments[memberID] = currentAssignment[memberID] |
| delete(currentAssignment, memberID) |
| sortedCurrentSubscriptions = sortMemberIDsByPartitionAssignments(currentAssignment) |
| } |
| } |
| |
| // create a deep copy of the current assignment so we can revert to it if we do not get a more balanced assignment later |
| preBalanceAssignment := deepCopyAssignment(currentAssignment) |
| preBalancePartitionConsumers := make(map[topicPartitionAssignment]string, len(currentPartitionConsumer)) |
| for k, v := range currentPartitionConsumer { |
| preBalancePartitionConsumers[k] = v |
| } |
| |
| reassignmentPerformed := s.performReassignments(sortedPartitions, currentAssignment, prevAssignment, sortedCurrentSubscriptions, consumer2AllPotentialPartitions, partition2AllPotentialConsumers, currentPartitionConsumer) |
| |
| // if we are not preserving existing assignments and we have made changes to the current assignment |
| // make sure we are getting a more balanced assignment; otherwise, revert to previous assignment |
| if !initializing && reassignmentPerformed && getBalanceScore(currentAssignment) >= getBalanceScore(preBalanceAssignment) { |
| currentAssignment = deepCopyAssignment(preBalanceAssignment) |
| currentPartitionConsumer = make(map[topicPartitionAssignment]string, len(preBalancePartitionConsumers)) |
| for k, v := range preBalancePartitionConsumers { |
| currentPartitionConsumer[k] = v |
| } |
| } |
| |
| // add the fixed assignments (those that could not change) back |
| for consumer, assignments := range fixedAssignments { |
| currentAssignment[consumer] = assignments |
| } |
| } |
| |
| // BalanceStrategyRoundRobin assigns partitions to members in alternating order. |
| // For example, there are two topics (t0, t1) and two consumer (m0, m1), and each topic has three partitions (p0, p1, p2): |
| // M0: [t0p0, t0p2, t1p1] |
| // M1: [t0p1, t1p0, t1p2] |
| var BalanceStrategyRoundRobin = new(roundRobinBalancer) |
| |
| type roundRobinBalancer struct{} |
| |
| func (b *roundRobinBalancer) Name() string { |
| return RoundRobinBalanceStrategyName |
| } |
| |
| func (b *roundRobinBalancer) Plan(memberAndMetadata map[string]ConsumerGroupMemberMetadata, topics map[string][]int32) (BalanceStrategyPlan, error) { |
| if len(memberAndMetadata) == 0 || len(topics) == 0 { |
| return nil, errors.New("members and topics are not provided") |
| } |
| // sort partitions |
| var topicPartitions []topicAndPartition |
| for topic, partitions := range topics { |
| for _, partition := range partitions { |
| topicPartitions = append(topicPartitions, topicAndPartition{topic: topic, partition: partition}) |
| } |
| } |
| sort.SliceStable(topicPartitions, func(i, j int) bool { |
| pi := topicPartitions[i] |
| pj := topicPartitions[j] |
| return pi.comparedValue() < pj.comparedValue() |
| }) |
| |
| // sort members |
| var members []memberAndTopic |
| for memberID, meta := range memberAndMetadata { |
| m := memberAndTopic{ |
| memberID: memberID, |
| topics: make(map[string]struct{}), |
| } |
| for _, t := range meta.Topics { |
| m.topics[t] = struct{}{} |
| } |
| members = append(members, m) |
| } |
| sort.SliceStable(members, func(i, j int) bool { |
| mi := members[i] |
| mj := members[j] |
| return mi.memberID < mj.memberID |
| }) |
| |
| // assign partitions |
| plan := make(BalanceStrategyPlan, len(members)) |
| i := 0 |
| n := len(members) |
| for _, tp := range topicPartitions { |
| m := members[i%n] |
| for !m.hasTopic(tp.topic) { |
| i++ |
| m = members[i%n] |
| } |
| plan.Add(m.memberID, tp.topic, tp.partition) |
| i++ |
| } |
| return plan, nil |
| } |
| |
| func (b *roundRobinBalancer) AssignmentData(memberID string, topics map[string][]int32, generationID int32) ([]byte, error) { |
| return nil, nil // do nothing for now |
| } |
| |
| type topicAndPartition struct { |
| topic string |
| partition int32 |
| } |
| |
| func (tp *topicAndPartition) comparedValue() string { |
| return fmt.Sprintf("%s-%d", tp.topic, tp.partition) |
| } |
| |
| type memberAndTopic struct { |
| memberID string |
| topics map[string]struct{} |
| } |
| |
| func (m *memberAndTopic) hasTopic(topic string) bool { |
| _, isExist := m.topics[topic] |
| return isExist |
| } |
| |
| // Calculate the balance score of the given assignment, as the sum of assigned partitions size difference of all consumer pairs. |
| // A perfectly balanced assignment (with all consumers getting the same number of partitions) has a balance score of 0. |
| // Lower balance score indicates a more balanced assignment. |
| func getBalanceScore(assignment map[string][]topicPartitionAssignment) int { |
| consumer2AssignmentSize := make(map[string]int, len(assignment)) |
| for memberID, partitions := range assignment { |
| consumer2AssignmentSize[memberID] = len(partitions) |
| } |
| |
| var score float64 |
| for memberID, consumerAssignmentSize := range consumer2AssignmentSize { |
| delete(consumer2AssignmentSize, memberID) |
| for _, otherConsumerAssignmentSize := range consumer2AssignmentSize { |
| score += math.Abs(float64(consumerAssignmentSize - otherConsumerAssignmentSize)) |
| } |
| } |
| return int(score) |
| } |
| |
| // Determine whether the current assignment plan is balanced. |
| func isBalanced(currentAssignment map[string][]topicPartitionAssignment, allSubscriptions map[string][]topicPartitionAssignment) bool { |
| sortedCurrentSubscriptions := sortMemberIDsByPartitionAssignments(currentAssignment) |
| min := len(currentAssignment[sortedCurrentSubscriptions[0]]) |
| max := len(currentAssignment[sortedCurrentSubscriptions[len(sortedCurrentSubscriptions)-1]]) |
| if min >= max-1 { |
| // if minimum and maximum numbers of partitions assigned to consumers differ by at most one return true |
| return true |
| } |
| |
| // create a mapping from partitions to the consumer assigned to them |
| allPartitions := make(map[topicPartitionAssignment]string) |
| for memberID, partitions := range currentAssignment { |
| for _, partition := range partitions { |
| if _, exists := allPartitions[partition]; exists { |
| Logger.Printf("Topic %s Partition %d is assigned more than one consumer", partition.Topic, partition.Partition) |
| } |
| allPartitions[partition] = memberID |
| } |
| } |
| |
| // for each consumer that does not have all the topic partitions it can get make sure none of the topic partitions it |
| // could but did not get cannot be moved to it (because that would break the balance) |
| for _, memberID := range sortedCurrentSubscriptions { |
| consumerPartitions := currentAssignment[memberID] |
| consumerPartitionCount := len(consumerPartitions) |
| |
| // skip if this consumer already has all the topic partitions it can get |
| if consumerPartitionCount == len(allSubscriptions[memberID]) { |
| continue |
| } |
| |
| // otherwise make sure it cannot get any more |
| potentialTopicPartitions := allSubscriptions[memberID] |
| for _, partition := range potentialTopicPartitions { |
| if !memberAssignmentsIncludeTopicPartition(currentAssignment[memberID], partition) { |
| otherConsumer := allPartitions[partition] |
| otherConsumerPartitionCount := len(currentAssignment[otherConsumer]) |
| if consumerPartitionCount < otherConsumerPartitionCount { |
| return false |
| } |
| } |
| } |
| } |
| return true |
| } |
| |
| // Reassign all topic partitions that need reassignment until balanced. |
| func (s *stickyBalanceStrategy) performReassignments(reassignablePartitions []topicPartitionAssignment, currentAssignment map[string][]topicPartitionAssignment, prevAssignment map[topicPartitionAssignment]consumerGenerationPair, sortedCurrentSubscriptions []string, consumer2AllPotentialPartitions map[string][]topicPartitionAssignment, partition2AllPotentialConsumers map[topicPartitionAssignment][]string, currentPartitionConsumer map[topicPartitionAssignment]string) bool { |
| reassignmentPerformed := false |
| modified := false |
| |
| // repeat reassignment until no partition can be moved to improve the balance |
| for { |
| modified = false |
| // reassign all reassignable partitions (starting from the partition with least potential consumers and if needed) |
| // until the full list is processed or a balance is achieved |
| for _, partition := range reassignablePartitions { |
| if isBalanced(currentAssignment, consumer2AllPotentialPartitions) { |
| break |
| } |
| |
| // the partition must have at least two consumers |
| if len(partition2AllPotentialConsumers[partition]) <= 1 { |
| Logger.Printf("Expected more than one potential consumer for partition %s topic %d", partition.Topic, partition.Partition) |
| } |
| |
| // the partition must have a consumer |
| consumer := currentPartitionConsumer[partition] |
| if consumer == "" { |
| Logger.Printf("Expected topic %s partition %d to be assigned to a consumer", partition.Topic, partition.Partition) |
| } |
| |
| if _, exists := prevAssignment[partition]; exists { |
| if len(currentAssignment[consumer]) > (len(currentAssignment[prevAssignment[partition].MemberID]) + 1) { |
| sortedCurrentSubscriptions = s.reassignPartition(partition, currentAssignment, sortedCurrentSubscriptions, currentPartitionConsumer, prevAssignment[partition].MemberID) |
| reassignmentPerformed = true |
| modified = true |
| continue |
| } |
| } |
| |
| // check if a better-suited consumer exists for the partition; if so, reassign it |
| for _, otherConsumer := range partition2AllPotentialConsumers[partition] { |
| if len(currentAssignment[consumer]) > (len(currentAssignment[otherConsumer]) + 1) { |
| sortedCurrentSubscriptions = s.reassignPartitionToNewConsumer(partition, currentAssignment, sortedCurrentSubscriptions, currentPartitionConsumer, consumer2AllPotentialPartitions) |
| reassignmentPerformed = true |
| modified = true |
| break |
| } |
| } |
| } |
| if !modified { |
| return reassignmentPerformed |
| } |
| } |
| } |
| |
| // Identify a new consumer for a topic partition and reassign it. |
| func (s *stickyBalanceStrategy) reassignPartitionToNewConsumer(partition topicPartitionAssignment, currentAssignment map[string][]topicPartitionAssignment, sortedCurrentSubscriptions []string, currentPartitionConsumer map[topicPartitionAssignment]string, consumer2AllPotentialPartitions map[string][]topicPartitionAssignment) []string { |
| for _, anotherConsumer := range sortedCurrentSubscriptions { |
| if memberAssignmentsIncludeTopicPartition(consumer2AllPotentialPartitions[anotherConsumer], partition) { |
| return s.reassignPartition(partition, currentAssignment, sortedCurrentSubscriptions, currentPartitionConsumer, anotherConsumer) |
| } |
| } |
| return sortedCurrentSubscriptions |
| } |
| |
| // Reassign a specific partition to a new consumer |
| func (s *stickyBalanceStrategy) reassignPartition(partition topicPartitionAssignment, currentAssignment map[string][]topicPartitionAssignment, sortedCurrentSubscriptions []string, currentPartitionConsumer map[topicPartitionAssignment]string, newConsumer string) []string { |
| consumer := currentPartitionConsumer[partition] |
| // find the correct partition movement considering the stickiness requirement |
| partitionToBeMoved := s.movements.getTheActualPartitionToBeMoved(partition, consumer, newConsumer) |
| return s.processPartitionMovement(partitionToBeMoved, newConsumer, currentAssignment, sortedCurrentSubscriptions, currentPartitionConsumer) |
| } |
| |
| // Track the movement of a topic partition after assignment |
| func (s *stickyBalanceStrategy) processPartitionMovement(partition topicPartitionAssignment, newConsumer string, currentAssignment map[string][]topicPartitionAssignment, sortedCurrentSubscriptions []string, currentPartitionConsumer map[topicPartitionAssignment]string) []string { |
| oldConsumer := currentPartitionConsumer[partition] |
| s.movements.movePartition(partition, oldConsumer, newConsumer) |
| |
| currentAssignment[oldConsumer] = removeTopicPartitionFromMemberAssignments(currentAssignment[oldConsumer], partition) |
| currentAssignment[newConsumer] = append(currentAssignment[newConsumer], partition) |
| currentPartitionConsumer[partition] = newConsumer |
| return sortMemberIDsByPartitionAssignments(currentAssignment) |
| } |
| |
| // Determine whether a specific consumer should be considered for topic partition assignment. |
| func canConsumerParticipateInReassignment(memberID string, currentAssignment map[string][]topicPartitionAssignment, consumer2AllPotentialPartitions map[string][]topicPartitionAssignment, partition2AllPotentialConsumers map[topicPartitionAssignment][]string) bool { |
| currentPartitions := currentAssignment[memberID] |
| currentAssignmentSize := len(currentPartitions) |
| maxAssignmentSize := len(consumer2AllPotentialPartitions[memberID]) |
| if currentAssignmentSize > maxAssignmentSize { |
| Logger.Printf("The consumer %s is assigned more partitions than the maximum possible", memberID) |
| } |
| if currentAssignmentSize < maxAssignmentSize { |
| // if a consumer is not assigned all its potential partitions it is subject to reassignment |
| return true |
| } |
| for _, partition := range currentPartitions { |
| if canTopicPartitionParticipateInReassignment(partition, partition2AllPotentialConsumers) { |
| return true |
| } |
| } |
| return false |
| } |
| |
| // Only consider reassigning those topic partitions that have two or more potential consumers. |
| func canTopicPartitionParticipateInReassignment(partition topicPartitionAssignment, partition2AllPotentialConsumers map[topicPartitionAssignment][]string) bool { |
| return len(partition2AllPotentialConsumers[partition]) >= 2 |
| } |
| |
| // The assignment should improve the overall balance of the partition assignments to consumers. |
| func assignPartition(partition topicPartitionAssignment, sortedCurrentSubscriptions []string, currentAssignment map[string][]topicPartitionAssignment, consumer2AllPotentialPartitions map[string][]topicPartitionAssignment, currentPartitionConsumer map[topicPartitionAssignment]string) []string { |
| for _, memberID := range sortedCurrentSubscriptions { |
| if memberAssignmentsIncludeTopicPartition(consumer2AllPotentialPartitions[memberID], partition) { |
| currentAssignment[memberID] = append(currentAssignment[memberID], partition) |
| currentPartitionConsumer[partition] = memberID |
| break |
| } |
| } |
| return sortMemberIDsByPartitionAssignments(currentAssignment) |
| } |
| |
| // Deserialize topic partition assignment data to aid with creation of a sticky assignment. |
| func deserializeTopicPartitionAssignment(userDataBytes []byte) (StickyAssignorUserData, error) { |
| userDataV1 := &StickyAssignorUserDataV1{} |
| if err := decode(userDataBytes, userDataV1); err != nil { |
| userDataV0 := &StickyAssignorUserDataV0{} |
| if err := decode(userDataBytes, userDataV0); err != nil { |
| return nil, err |
| } |
| return userDataV0, nil |
| } |
| return userDataV1, nil |
| } |
| |
| // filterAssignedPartitions returns a map of consumer group members to their list of previously-assigned topic partitions, limited |
| // to those topic partitions currently reported by the Kafka cluster. |
| func filterAssignedPartitions(currentAssignment map[string][]topicPartitionAssignment, partition2AllPotentialConsumers map[topicPartitionAssignment][]string) map[string][]topicPartitionAssignment { |
| assignments := deepCopyAssignment(currentAssignment) |
| for memberID, partitions := range assignments { |
| // perform in-place filtering |
| i := 0 |
| for _, partition := range partitions { |
| if _, exists := partition2AllPotentialConsumers[partition]; exists { |
| partitions[i] = partition |
| i++ |
| } |
| } |
| assignments[memberID] = partitions[:i] |
| } |
| return assignments |
| } |
| |
| func removeTopicPartitionFromMemberAssignments(assignments []topicPartitionAssignment, topic topicPartitionAssignment) []topicPartitionAssignment { |
| for i, assignment := range assignments { |
| if assignment == topic { |
| return append(assignments[:i], assignments[i+1:]...) |
| } |
| } |
| return assignments |
| } |
| |
| func memberAssignmentsIncludeTopicPartition(assignments []topicPartitionAssignment, topic topicPartitionAssignment) bool { |
| for _, assignment := range assignments { |
| if assignment == topic { |
| return true |
| } |
| } |
| return false |
| } |
| |
| func sortPartitions(currentAssignment map[string][]topicPartitionAssignment, partitionsWithADifferentPreviousAssignment map[topicPartitionAssignment]consumerGenerationPair, isFreshAssignment bool, partition2AllPotentialConsumers map[topicPartitionAssignment][]string, consumer2AllPotentialPartitions map[string][]topicPartitionAssignment) []topicPartitionAssignment { |
| unassignedPartitions := make(map[topicPartitionAssignment]bool, len(partition2AllPotentialConsumers)) |
| for partition := range partition2AllPotentialConsumers { |
| unassignedPartitions[partition] = true |
| } |
| |
| sortedPartitions := make([]topicPartitionAssignment, 0) |
| if !isFreshAssignment && areSubscriptionsIdentical(partition2AllPotentialConsumers, consumer2AllPotentialPartitions) { |
| // if this is a reassignment and the subscriptions are identical (all consumers can consumer from all topics) |
| // then we just need to simply list partitions in a round robin fashion (from consumers with |
| // most assigned partitions to those with least) |
| assignments := filterAssignedPartitions(currentAssignment, partition2AllPotentialConsumers) |
| |
| // use priority-queue to evaluate consumer group members in descending-order based on |
| // the number of topic partition assignments (i.e. consumers with most assignments first) |
| pq := make(assignmentPriorityQueue, len(assignments)) |
| i := 0 |
| for consumerID, consumerAssignments := range assignments { |
| pq[i] = &consumerGroupMember{ |
| id: consumerID, |
| assignments: consumerAssignments, |
| } |
| i++ |
| } |
| heap.Init(&pq) |
| |
| for { |
| // loop until no consumer-group members remain |
| if pq.Len() == 0 { |
| break |
| } |
| member := pq[0] |
| |
| // partitions that were assigned to a different consumer last time |
| var prevPartitionIndex int |
| for i, partition := range member.assignments { |
| if _, exists := partitionsWithADifferentPreviousAssignment[partition]; exists { |
| prevPartitionIndex = i |
| break |
| } |
| } |
| |
| if len(member.assignments) > 0 { |
| partition := member.assignments[prevPartitionIndex] |
| sortedPartitions = append(sortedPartitions, partition) |
| delete(unassignedPartitions, partition) |
| if prevPartitionIndex == 0 { |
| member.assignments = member.assignments[1:] |
| } else { |
| member.assignments = append(member.assignments[:prevPartitionIndex], member.assignments[prevPartitionIndex+1:]...) |
| } |
| heap.Fix(&pq, 0) |
| } else { |
| heap.Pop(&pq) |
| } |
| } |
| |
| for partition := range unassignedPartitions { |
| sortedPartitions = append(sortedPartitions, partition) |
| } |
| } else { |
| // an ascending sorted set of topic partitions based on how many consumers can potentially use them |
| sortedPartitions = sortPartitionsByPotentialConsumerAssignments(partition2AllPotentialConsumers) |
| } |
| return sortedPartitions |
| } |
| |
| func sortMemberIDsByPartitionAssignments(assignments map[string][]topicPartitionAssignment) []string { |
| // sort the members by the number of partition assignments in ascending order |
| sortedMemberIDs := make([]string, 0, len(assignments)) |
| for memberID := range assignments { |
| sortedMemberIDs = append(sortedMemberIDs, memberID) |
| } |
| sort.SliceStable(sortedMemberIDs, func(i, j int) bool { |
| ret := len(assignments[sortedMemberIDs[i]]) - len(assignments[sortedMemberIDs[j]]) |
| if ret == 0 { |
| return sortedMemberIDs[i] < sortedMemberIDs[j] |
| } |
| return len(assignments[sortedMemberIDs[i]]) < len(assignments[sortedMemberIDs[j]]) |
| }) |
| return sortedMemberIDs |
| } |
| |
| func sortPartitionsByPotentialConsumerAssignments(partition2AllPotentialConsumers map[topicPartitionAssignment][]string) []topicPartitionAssignment { |
| // sort the members by the number of partition assignments in descending order |
| sortedPartionIDs := make([]topicPartitionAssignment, len(partition2AllPotentialConsumers)) |
| i := 0 |
| for partition := range partition2AllPotentialConsumers { |
| sortedPartionIDs[i] = partition |
| i++ |
| } |
| sort.Slice(sortedPartionIDs, func(i, j int) bool { |
| if len(partition2AllPotentialConsumers[sortedPartionIDs[i]]) == len(partition2AllPotentialConsumers[sortedPartionIDs[j]]) { |
| ret := strings.Compare(sortedPartionIDs[i].Topic, sortedPartionIDs[j].Topic) |
| if ret == 0 { |
| return sortedPartionIDs[i].Partition < sortedPartionIDs[j].Partition |
| } |
| return ret < 0 |
| } |
| return len(partition2AllPotentialConsumers[sortedPartionIDs[i]]) < len(partition2AllPotentialConsumers[sortedPartionIDs[j]]) |
| }) |
| return sortedPartionIDs |
| } |
| |
| func deepCopyAssignment(assignment map[string][]topicPartitionAssignment) map[string][]topicPartitionAssignment { |
| m := make(map[string][]topicPartitionAssignment, len(assignment)) |
| for memberID, subscriptions := range assignment { |
| m[memberID] = append(subscriptions[:0:0], subscriptions...) |
| } |
| return m |
| } |
| |
| func areSubscriptionsIdentical(partition2AllPotentialConsumers map[topicPartitionAssignment][]string, consumer2AllPotentialPartitions map[string][]topicPartitionAssignment) bool { |
| curMembers := make(map[string]int) |
| for _, cur := range partition2AllPotentialConsumers { |
| if len(curMembers) == 0 { |
| for _, curMembersElem := range cur { |
| curMembers[curMembersElem]++ |
| } |
| continue |
| } |
| |
| if len(curMembers) != len(cur) { |
| return false |
| } |
| |
| yMap := make(map[string]int) |
| for _, yElem := range cur { |
| yMap[yElem]++ |
| } |
| |
| for curMembersMapKey, curMembersMapVal := range curMembers { |
| if yMap[curMembersMapKey] != curMembersMapVal { |
| return false |
| } |
| } |
| } |
| |
| curPartitions := make(map[topicPartitionAssignment]int) |
| for _, cur := range consumer2AllPotentialPartitions { |
| if len(curPartitions) == 0 { |
| for _, curPartitionElem := range cur { |
| curPartitions[curPartitionElem]++ |
| } |
| continue |
| } |
| |
| if len(curPartitions) != len(cur) { |
| return false |
| } |
| |
| yMap := make(map[topicPartitionAssignment]int) |
| for _, yElem := range cur { |
| yMap[yElem]++ |
| } |
| |
| for curMembersMapKey, curMembersMapVal := range curPartitions { |
| if yMap[curMembersMapKey] != curMembersMapVal { |
| return false |
| } |
| } |
| } |
| return true |
| } |
| |
| // We need to process subscriptions' user data with each consumer's reported generation in mind |
| // higher generations overwrite lower generations in case of a conflict |
| // note that a conflict could exist only if user data is for different generations |
| func prepopulateCurrentAssignments(members map[string]ConsumerGroupMemberMetadata) (map[string][]topicPartitionAssignment, map[topicPartitionAssignment]consumerGenerationPair, error) { |
| currentAssignment := make(map[string][]topicPartitionAssignment) |
| prevAssignment := make(map[topicPartitionAssignment]consumerGenerationPair) |
| |
| // for each partition we create a sorted map of its consumers by generation |
| sortedPartitionConsumersByGeneration := make(map[topicPartitionAssignment]map[int]string) |
| for memberID, meta := range members { |
| consumerUserData, err := deserializeTopicPartitionAssignment(meta.UserData) |
| if err != nil { |
| return nil, nil, err |
| } |
| for _, partition := range consumerUserData.partitions() { |
| if consumers, exists := sortedPartitionConsumersByGeneration[partition]; exists { |
| if consumerUserData.hasGeneration() { |
| if _, generationExists := consumers[consumerUserData.generation()]; generationExists { |
| // same partition is assigned to two consumers during the same rebalance. |
| // log a warning and skip this record |
| Logger.Printf("Topic %s Partition %d is assigned to multiple consumers following sticky assignment generation %d", partition.Topic, partition.Partition, consumerUserData.generation()) |
| continue |
| } else { |
| consumers[consumerUserData.generation()] = memberID |
| } |
| } else { |
| consumers[defaultGeneration] = memberID |
| } |
| } else { |
| generation := defaultGeneration |
| if consumerUserData.hasGeneration() { |
| generation = consumerUserData.generation() |
| } |
| sortedPartitionConsumersByGeneration[partition] = map[int]string{generation: memberID} |
| } |
| } |
| } |
| |
| // prevAssignment holds the prior ConsumerGenerationPair (before current) of each partition |
| // current and previous consumers are the last two consumers of each partition in the above sorted map |
| for partition, consumers := range sortedPartitionConsumersByGeneration { |
| // sort consumers by generation in decreasing order |
| var generations []int |
| for generation := range consumers { |
| generations = append(generations, generation) |
| } |
| sort.Sort(sort.Reverse(sort.IntSlice(generations))) |
| |
| consumer := consumers[generations[0]] |
| if _, exists := currentAssignment[consumer]; !exists { |
| currentAssignment[consumer] = []topicPartitionAssignment{partition} |
| } else { |
| currentAssignment[consumer] = append(currentAssignment[consumer], partition) |
| } |
| |
| // check for previous assignment, if any |
| if len(generations) > 1 { |
| prevAssignment[partition] = consumerGenerationPair{ |
| MemberID: consumers[generations[1]], |
| Generation: generations[1], |
| } |
| } |
| } |
| return currentAssignment, prevAssignment, nil |
| } |
| |
| type consumerGenerationPair struct { |
| MemberID string |
| Generation int |
| } |
| |
| // consumerPair represents a pair of Kafka consumer ids involved in a partition reassignment. |
| type consumerPair struct { |
| SrcMemberID string |
| DstMemberID string |
| } |
| |
| // partitionMovements maintains some data structures to simplify lookup of partition movements among consumers. |
| type partitionMovements struct { |
| PartitionMovementsByTopic map[string]map[consumerPair]map[topicPartitionAssignment]bool |
| Movements map[topicPartitionAssignment]consumerPair |
| } |
| |
| func (p *partitionMovements) removeMovementRecordOfPartition(partition topicPartitionAssignment) consumerPair { |
| pair := p.Movements[partition] |
| delete(p.Movements, partition) |
| |
| partitionMovementsForThisTopic := p.PartitionMovementsByTopic[partition.Topic] |
| delete(partitionMovementsForThisTopic[pair], partition) |
| if len(partitionMovementsForThisTopic[pair]) == 0 { |
| delete(partitionMovementsForThisTopic, pair) |
| } |
| if len(p.PartitionMovementsByTopic[partition.Topic]) == 0 { |
| delete(p.PartitionMovementsByTopic, partition.Topic) |
| } |
| return pair |
| } |
| |
| func (p *partitionMovements) addPartitionMovementRecord(partition topicPartitionAssignment, pair consumerPair) { |
| p.Movements[partition] = pair |
| if _, exists := p.PartitionMovementsByTopic[partition.Topic]; !exists { |
| p.PartitionMovementsByTopic[partition.Topic] = make(map[consumerPair]map[topicPartitionAssignment]bool) |
| } |
| partitionMovementsForThisTopic := p.PartitionMovementsByTopic[partition.Topic] |
| if _, exists := partitionMovementsForThisTopic[pair]; !exists { |
| partitionMovementsForThisTopic[pair] = make(map[topicPartitionAssignment]bool) |
| } |
| partitionMovementsForThisTopic[pair][partition] = true |
| } |
| |
| func (p *partitionMovements) movePartition(partition topicPartitionAssignment, oldConsumer, newConsumer string) { |
| pair := consumerPair{ |
| SrcMemberID: oldConsumer, |
| DstMemberID: newConsumer, |
| } |
| if _, exists := p.Movements[partition]; exists { |
| // this partition has previously moved |
| existingPair := p.removeMovementRecordOfPartition(partition) |
| if existingPair.DstMemberID != oldConsumer { |
| Logger.Printf("Existing pair DstMemberID %s was not equal to the oldConsumer ID %s", existingPair.DstMemberID, oldConsumer) |
| } |
| if existingPair.SrcMemberID != newConsumer { |
| // the partition is not moving back to its previous consumer |
| p.addPartitionMovementRecord(partition, consumerPair{ |
| SrcMemberID: existingPair.SrcMemberID, |
| DstMemberID: newConsumer, |
| }) |
| } |
| } else { |
| p.addPartitionMovementRecord(partition, pair) |
| } |
| } |
| |
| func (p *partitionMovements) getTheActualPartitionToBeMoved(partition topicPartitionAssignment, oldConsumer, newConsumer string) topicPartitionAssignment { |
| if _, exists := p.PartitionMovementsByTopic[partition.Topic]; !exists { |
| return partition |
| } |
| if _, exists := p.Movements[partition]; exists { |
| // this partition has previously moved |
| if oldConsumer != p.Movements[partition].DstMemberID { |
| Logger.Printf("Partition movement DstMemberID %s was not equal to the oldConsumer ID %s", p.Movements[partition].DstMemberID, oldConsumer) |
| } |
| oldConsumer = p.Movements[partition].SrcMemberID |
| } |
| |
| partitionMovementsForThisTopic := p.PartitionMovementsByTopic[partition.Topic] |
| reversePair := consumerPair{ |
| SrcMemberID: newConsumer, |
| DstMemberID: oldConsumer, |
| } |
| if _, exists := partitionMovementsForThisTopic[reversePair]; !exists { |
| return partition |
| } |
| var reversePairPartition topicPartitionAssignment |
| for otherPartition := range partitionMovementsForThisTopic[reversePair] { |
| reversePairPartition = otherPartition |
| } |
| return reversePairPartition |
| } |
| |
| func (p *partitionMovements) isLinked(src, dst string, pairs []consumerPair, currentPath []string) ([]string, bool) { |
| if src == dst { |
| return currentPath, false |
| } |
| if len(pairs) == 0 { |
| return currentPath, false |
| } |
| for _, pair := range pairs { |
| if src == pair.SrcMemberID && dst == pair.DstMemberID { |
| currentPath = append(currentPath, src, dst) |
| return currentPath, true |
| } |
| } |
| |
| for _, pair := range pairs { |
| if pair.SrcMemberID == src { |
| // create a deep copy of the pairs, excluding the current pair |
| reducedSet := make([]consumerPair, len(pairs)-1) |
| i := 0 |
| for _, p := range pairs { |
| if p != pair { |
| reducedSet[i] = pair |
| i++ |
| } |
| } |
| |
| currentPath = append(currentPath, pair.SrcMemberID) |
| return p.isLinked(pair.DstMemberID, dst, reducedSet, currentPath) |
| } |
| } |
| return currentPath, false |
| } |
| |
| func (p *partitionMovements) in(cycle []string, cycles [][]string) bool { |
| superCycle := make([]string, len(cycle)-1) |
| for i := 0; i < len(cycle)-1; i++ { |
| superCycle[i] = cycle[i] |
| } |
| superCycle = append(superCycle, cycle...) |
| for _, foundCycle := range cycles { |
| if len(foundCycle) == len(cycle) && indexOfSubList(superCycle, foundCycle) != -1 { |
| return true |
| } |
| } |
| return false |
| } |
| |
| func (p *partitionMovements) hasCycles(pairs []consumerPair) bool { |
| cycles := make([][]string, 0) |
| for _, pair := range pairs { |
| // create a deep copy of the pairs, excluding the current pair |
| reducedPairs := make([]consumerPair, len(pairs)-1) |
| i := 0 |
| for _, p := range pairs { |
| if p != pair { |
| reducedPairs[i] = pair |
| i++ |
| } |
| } |
| if path, linked := p.isLinked(pair.DstMemberID, pair.SrcMemberID, reducedPairs, []string{pair.SrcMemberID}); linked { |
| if !p.in(path, cycles) { |
| cycles = append(cycles, path) |
| Logger.Printf("A cycle of length %d was found: %v", len(path)-1, path) |
| } |
| } |
| } |
| |
| // for now we want to make sure there is no partition movements of the same topic between a pair of consumers. |
| // the odds of finding a cycle among more than two consumers seem to be very low (according to various randomized |
| // tests with the given sticky algorithm) that it should not worth the added complexity of handling those cases. |
| for _, cycle := range cycles { |
| if len(cycle) == 3 { |
| return true |
| } |
| } |
| return false |
| } |
| |
| func (p *partitionMovements) isSticky() bool { |
| for topic, movements := range p.PartitionMovementsByTopic { |
| movementPairs := make([]consumerPair, len(movements)) |
| i := 0 |
| for pair := range movements { |
| movementPairs[i] = pair |
| i++ |
| } |
| if p.hasCycles(movementPairs) { |
| Logger.Printf("Stickiness is violated for topic %s", topic) |
| Logger.Printf("Partition movements for this topic occurred among the following consumer pairs: %v", movements) |
| return false |
| } |
| } |
| return true |
| } |
| |
| func indexOfSubList(source []string, target []string) int { |
| targetSize := len(target) |
| maxCandidate := len(source) - targetSize |
| nextCand: |
| for candidate := 0; candidate <= maxCandidate; candidate++ { |
| j := candidate |
| for i := 0; i < targetSize; i++ { |
| if target[i] != source[j] { |
| // Element mismatch, try next cand |
| continue nextCand |
| } |
| j++ |
| } |
| // All elements of candidate matched target |
| return candidate |
| } |
| return -1 |
| } |
| |
| type consumerGroupMember struct { |
| id string |
| assignments []topicPartitionAssignment |
| } |
| |
| // assignmentPriorityQueue is a priority-queue of consumer group members that is sorted |
| // in descending order (most assignments to least assignments). |
| type assignmentPriorityQueue []*consumerGroupMember |
| |
| func (pq assignmentPriorityQueue) Len() int { return len(pq) } |
| |
| func (pq assignmentPriorityQueue) Less(i, j int) bool { |
| // order asssignment priority queue in descending order using assignment-count/member-id |
| if len(pq[i].assignments) == len(pq[j].assignments) { |
| return strings.Compare(pq[i].id, pq[j].id) > 0 |
| } |
| return len(pq[i].assignments) > len(pq[j].assignments) |
| } |
| |
| func (pq assignmentPriorityQueue) Swap(i, j int) { |
| pq[i], pq[j] = pq[j], pq[i] |
| } |
| |
| func (pq *assignmentPriorityQueue) Push(x interface{}) { |
| member := x.(*consumerGroupMember) |
| *pq = append(*pq, member) |
| } |
| |
| func (pq *assignmentPriorityQueue) Pop() interface{} { |
| old := *pq |
| n := len(old) |
| member := old[n-1] |
| *pq = old[0 : n-1] |
| return member |
| } |