vvcephei commented on a change in pull request #8497:
URL: https://github.com/apache/kafka/pull/8497#discussion_r411676361
##########
File path:
streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/TaskMovement.java
##########
@@ -16,128 +16,94 @@
*/
package org.apache.kafka.streams.processor.internals.assignment;
-import java.util.HashMap;
-import java.util.Iterator;
-import java.util.LinkedList;
+import static
org.apache.kafka.streams.processor.internals.assignment.AssignmentUtils.taskIsCaughtUpOnClient;
+
import java.util.List;
import java.util.Map;
-import java.util.Objects;
-import java.util.Set;
import java.util.SortedSet;
+import java.util.TreeSet;
import java.util.UUID;
import org.apache.kafka.streams.processor.TaskId;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
public class TaskMovement {
- private static final Logger log =
LoggerFactory.getLogger(TaskMovement.class);
-
final TaskId task;
- final UUID source;
- final UUID destination;
+ private final UUID destination;
- TaskMovement(final TaskId task, final UUID source, final UUID destination)
{
+ TaskMovement(final TaskId task, final UUID destination) {
this.task = task;
- this.source = source;
this.destination = destination;
}
- @Override
- public boolean equals(final Object o) {
- if (this == o) {
- return true;
- }
- if (o == null || getClass() != o.getClass()) {
- return false;
- }
- final TaskMovement movement = (TaskMovement) o;
- return Objects.equals(task, movement.task) &&
- Objects.equals(source, movement.source) &&
- Objects.equals(destination, movement.destination);
- }
-
- @Override
- public int hashCode() {
- return Objects.hash(task, source, destination);
- }
-
/**
- * Computes the movement of tasks from the state constrained to the
balanced assignment, up to the configured
- * {@code max.warmup.replicas}. A movement corresponds to a warmup replica
on the destination client, with
- * a few exceptional cases:
- * <p>
- * 1. Tasks whose destination clients are caught-up, or whose source
clients are not caught-up, will be moved
- * immediately from the source to the destination in the state constrained
assignment
- * 2. Tasks whose destination client previously had this task as a standby
will not be counted towards the total
- * {@code max.warmup.replicas}. Instead they will be counted against that
task's total {@code num.standby.replicas}.
- *
- * @param statefulActiveTaskAssignment the initial, state constrained
assignment, with the source clients
- * @param balancedStatefulActiveTaskAssignment the final, balanced
assignment, with the destination clients
- * @return list of the task movements from statefulActiveTaskAssignment to
balancedStatefulActiveTaskAssignment
+ * @return whether any warmup replicas were assigned
*/
- static List<TaskMovement> getMovements(final Map<UUID, List<TaskId>>
statefulActiveTaskAssignment,
- final Map<UUID, List<TaskId>>
balancedStatefulActiveTaskAssignment,
- final Map<TaskId, SortedSet<UUID>>
tasksToCaughtUpClients,
- final Map<UUID, ClientState>
clientStates,
- final Map<TaskId, Integer>
tasksToRemainingStandbys,
- final int maxWarmupReplicas) {
- if (statefulActiveTaskAssignment.size() !=
balancedStatefulActiveTaskAssignment.size()) {
- throw new IllegalStateException("Tried to compute movements but
assignments differ in size.");
- }
+ static boolean assignTaskMovements(final Map<UUID, List<TaskId>>
statefulActiveTaskAssignment,
+ final Map<TaskId, SortedSet<UUID>>
tasksToCaughtUpClients,
+ final Map<UUID, ClientState>
clientStates,
+ final Map<TaskId, Integer>
tasksToRemainingStandbys,
+ final int maxWarmupReplicas) {
+ boolean warmupReplicasAssigned = false;
+
+ final ValidClientsByTaskLoadQueue clientsByTaskLoad =
+ new ValidClientsByTaskLoadQueue(
+ clientStates,
+ (client, task) -> taskIsCaughtUpOnClient(task, client,
tasksToCaughtUpClients)
+ );
- final Map<TaskId, UUID> taskToDestinationClient = new HashMap<>();
- for (final Map.Entry<UUID, List<TaskId>> clientEntry :
balancedStatefulActiveTaskAssignment.entrySet()) {
- final UUID destination = clientEntry.getKey();
- for (final TaskId task : clientEntry.getValue()) {
- taskToDestinationClient.put(task, destination);
+ final SortedSet<TaskMovement> taskMovements = new TreeSet<>(
+ (movement, other) -> {
+ final int numCaughtUpClients =
tasksToCaughtUpClients.get(movement.task).size();
+ final int otherNumCaughtUpClients =
tasksToCaughtUpClients.get(other.task).size();
+ if (numCaughtUpClients != otherNumCaughtUpClients) {
+ return numCaughtUpClients - otherNumCaughtUpClients;
+ } else {
+ return movement.task.compareTo(other.task);
+ }
}
+ );
+
+ for (final Map.Entry<UUID, List<TaskId>> assignmentEntry :
statefulActiveTaskAssignment.entrySet()) {
+ final UUID client = assignmentEntry.getKey();
+ final ClientState state = clientStates.get(client);
+ for (final TaskId task : assignmentEntry.getValue()) {
+ if (taskIsCaughtUpOnClient(task, client,
tasksToCaughtUpClients)) {
+ state.assignActive(task);
+ } else {
+ final TaskMovement taskMovement = new TaskMovement(task,
client);
+ taskMovements.add(taskMovement);
+ }
+ }
+ clientsByTaskLoad.offer(client);
}
- int remainingAllowedWarmupReplicas = maxWarmupReplicas;
- final List<TaskMovement> movements = new LinkedList<>();
- for (final Map.Entry<UUID, List<TaskId>> sourceClientEntry :
statefulActiveTaskAssignment.entrySet()) {
- final UUID source = sourceClientEntry.getKey();
+ int remainingWarmupReplicas = maxWarmupReplicas;
+ for (final TaskMovement movement : taskMovements) {
+ final UUID leastLoadedClient =
clientsByTaskLoad.poll(movement.task);
+ if (leastLoadedClient == null) {
+ throw new IllegalStateException("Tried to move task to
caught-up client but none exist");
+ }
- final Iterator<TaskId> sourceClientTasksIterator =
sourceClientEntry.getValue().iterator();
- while (sourceClientTasksIterator.hasNext()) {
- final TaskId task = sourceClientTasksIterator.next();
- final UUID destination = taskToDestinationClient.get(task);
- if (destination == null) {
- log.error("Task {} is assigned to client {} in initial
assignment but has no owner in the final " +
- "balanced assignment.", task, source);
- throw new IllegalStateException("Found task in initial
assignment that was not assigned in the final.");
- } else if (!source.equals(destination)) {
- if (destinationClientIsCaughtUp(task, destination,
tasksToCaughtUpClients)) {
- sourceClientTasksIterator.remove();
-
statefulActiveTaskAssignment.get(destination).add(task);
- } else {
- if
(clientStates.get(destination).prevStandbyTasks().contains(task)
- && tasksToRemainingStandbys.get(task) > 0
- ) {
- decrementRemainingStandbys(task,
tasksToRemainingStandbys);
- } else {
- --remainingAllowedWarmupReplicas;
- }
+ final ClientState sourceClientState =
clientStates.get(leastLoadedClient);
+ sourceClientState.assignActive(movement.task);
- movements.add(new TaskMovement(task, source,
destination));
- if (remainingAllowedWarmupReplicas == 0) {
- return movements;
- }
- }
- }
+ final ClientState destinationClientState =
clientStates.get(movement.destination);
+ if
(destinationClientState.prevStandbyTasks().contains(movement.task) &&
tasksToRemainingStandbys.get(movement.task) > 0) {
Review comment:
I think we're trying to strike a balance of not harming HA while moving
tasks around.
So if we have a task T and three nodes A, B[T=active], C[T=standby], and we
want to move T to A, then we'll do it by assigning a warmup to A and letting B
continue to be active and C continue to be a standby until A catches up.
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