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fix rebalancing-tasks bug and added tests #900

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Apr 12, 2022
Merged

fix rebalancing-tasks bug and added tests #900

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2cdffef
fix rebalancing-tasks bug and added tests
Mar 25, 2022
dc588b4
add some more test cases with even number of instances and with singl…
Mar 29, 2022
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3 changes: 2 additions & 1 deletion ...rver/src/main/java/com/linkedin/datastream/server/assignment/StickyMulticastStrategy.java
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Original file line number Diff line number Diff line change
Expand Up @@ -205,7 +205,8 @@ public Map<String, Set<DatastreamTask>> assign(List<DatastreamGroup> datastreams
int minTasksPerInstance = tasksTotal / instances.size();

// some rebalance to increase the task count in instances below the minTasksPerInstance
while (newAssignment.get(instancesBySize.get(0)).size() < minTasksPerInstance) {
while (newAssignment.get(instancesBySize.get(0)).size() + _imbalanceThreshold < newAssignment.get(
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This is a lot to parse in one line. Consider pulling out into a couple vars so the logic is more obvious.

instancesBySize.get(instancesBySize.size() - 1)).size()) {
String smallInstance = instancesBySize.get(0);
String largeInstance = instancesBySize.get(instancesBySize.size() - 1);

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76 changes: 76 additions & 0 deletions .../src/test/java/com/linkedin/datastream/server/assignment/TestStickyMulticastStrategy.java
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Expand Up @@ -7,9 +7,11 @@

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
Expand Down Expand Up @@ -499,6 +501,80 @@ public void testExtraTasksAreNotAssignedDuringReassignment() {
}
}

@Test
public void testReBalancingTasksWithThreshold() {
String[] instances = new String[]{"instance1", "instance2", "instance3"};
reBalancingTasksWithThresholdHelper(instances, new int[]{9, 9, 13}, 1);
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reBalancingTasksWithThresholdHelper(instances, new int[]{9, 9, 13}, 2);
reBalancingTasksWithThresholdHelper(instances, new int[]{9, 9, 13}, 3);

reBalancingTasksWithThresholdHelper(instances, new int[]{1, 10, 20}, 1);
reBalancingTasksWithThresholdHelper(instances, new int[]{1, 10, 20}, 2);
reBalancingTasksWithThresholdHelper(instances, new int[]{1, 10, 20}, 3);

reBalancingTasksWithThresholdHelper(instances, new int[]{5, 5, 5}, 1);
reBalancingTasksWithThresholdHelper(instances, new int[]{5, 5, 5}, 2);
reBalancingTasksWithThresholdHelper(instances, new int[]{5, 5, 5}, 3);

instances = new String[]{"instance1", "instance2"};
reBalancingTasksWithThresholdHelper(instances, new int[]{9, 13}, 1);
reBalancingTasksWithThresholdHelper(instances, new int[]{9, 13}, 2);
reBalancingTasksWithThresholdHelper(instances, new int[]{9, 13}, 3);

reBalancingTasksWithThresholdHelper(instances, new int[]{1, 10}, 1);
reBalancingTasksWithThresholdHelper(instances, new int[]{1, 10}, 2);
reBalancingTasksWithThresholdHelper(instances, new int[]{1, 10}, 3);

reBalancingTasksWithThresholdHelper(instances, new int[]{5, 5}, 1);
reBalancingTasksWithThresholdHelper(instances, new int[]{5, 5}, 2);
reBalancingTasksWithThresholdHelper(instances, new int[]{5, 5}, 3);

instances = new String[]{"instance1"};
reBalancingTasksWithThresholdHelper(instances, new int[]{9}, 1);
reBalancingTasksWithThresholdHelper(instances, new int[]{9}, 2);
reBalancingTasksWithThresholdHelper(instances, new int[]{9}, 3);
}

// this helper function tests the rebalancing of tasks with an imbalance threshold across the instances
// with StickyMulticastStrategy
private void reBalancingTasksWithThresholdHelper(String[] instances, int[] taskDistribution, int imbalanceThreshold) {
List<DatastreamGroup> datastreams = generateDatastreams("ds", 1);
StickyMulticastStrategy strategy = new StickyMulticastStrategy(Optional.empty(), imbalanceThreshold);

// create a dummy current assignment following the parameterized task distribution; based on which the
// new assignment will be generated.
HashMap<String, Set<DatastreamTask>> currentDummyAssignment = new HashMap<>();
for (int index = 0; index < instances.length; index += 1) {
currentDummyAssignment.put(instances[index],
getDummyTasksSet(taskDistribution[index], datastreams.get(0).getDatastreams()));
}

int totalNumberTasks = currentDummyAssignment.values().stream().mapToInt(Collection::size).sum();
// setting the total count of tasks as the max tasks for our single datastream, so that the new assignment
// distribution looks similar to the current assignment.
datastreams.get(0).getDatastreams().get(0).getMetadata().put(CFG_MAX_TASKS, Integer.toString(totalNumberTasks));

Map<String, Set<DatastreamTask>> assignment =
strategy.assign(datastreams, Arrays.asList(instances), currentDummyAssignment);

Arrays.sort(instances, Comparator.comparing(x -> assignment.get(x).size()));

int minTasksAssignedToInstance = assignment.get(instances[0]).size();
int maxTasksAssignedToInstance = assignment.get(instances[instances.length - 1]).size();

Assert.assertTrue(maxTasksAssignedToInstance - minTasksAssignedToInstance <= imbalanceThreshold);
}

// returns a dummy set with #numTasks tasks
private HashSet<DatastreamTask> getDummyTasksSet(int numTasks, List<Datastream> datastreams) {
HashSet<DatastreamTask> assignedTasks = new HashSet<>();
while (numTasks > 0) {
assignedTasks.add(new DatastreamTaskImpl(datastreams));
numTasks -= 1;
}
return assignedTasks;
}

private static String assignmentToString(Map<String, Set<DatastreamTask>> assignment) {
StringBuilder builder = new StringBuilder();
assignment.keySet().stream().sorted().forEach(instance -> {
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