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[fix][broker] Fix ordering issue with ConsistentHashingStickyKeyConsu…
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…merSelector
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@lhotari
lhotari committed Sep 20, 2024
1 parent 105192d commit 12577d5
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172 changes: 139 additions & 33 deletions ...ain/java/org/apache/pulsar/broker/service/ConsistentHashingStickyKeyConsumerSelector.java
View file
Original file line number Diff line number Diff line change
Expand Up @@ -18,17 +18,19 @@
*/
package org.apache.pulsar.broker.service;

import com.google.common.collect.Lists;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.NavigableMap;
import java.util.TreeMap;
import java.util.WeakHashMap;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import org.apache.commons.lang3.mutable.MutableInt;
import org.apache.pulsar.client.api.Range;
import org.apache.pulsar.common.util.Murmur3_32Hash;

Expand All @@ -44,15 +46,118 @@ public class ConsistentHashingStickyKeyConsumerSelector implements StickyKeyCons
private final ReadWriteLock rwLock = new ReentrantReadWriteLock();

// Consistent-Hash ring
private final NavigableMap<Integer, List<Consumer>> hashRing;
private final NavigableMap<Integer, HashRingEntry> hashRing;
// used for distributing consumer instance selections evenly in the hash ring when there
// are multiple instances of consumer with the same consumer name or when there are hash collisions
private final Map<Consumer, MutableInt> consumerSelectionCounters;

private final int numberOfPoints;

public ConsistentHashingStickyKeyConsumerSelector(int numberOfPoints) {
this.hashRing = new TreeMap<>();
this.consumerSelectionCounters = new WeakHashMap<>();
this.numberOfPoints = numberOfPoints;
}

/**
* This class is used to store the consumers and the selected consumer for a hash value in the hash ring.
* This attempts to distribute the consumers evenly in the hash ring for consumers with the same
* consumer name and priority level. These entries collide in the hash ring.
* The selected consumer is the consumer that is selected to serve the hash value.
* It is not changed unless a consumer is removed or a colliding consumer with higher priority or
* lower selection count is added.
*/
private static class HashRingEntry {
// This class is used to store the consumer which it was added to the hash ring
// sorting will be by priority, consumer name and usage count of the consumer instance
record ConsumerEntry(Consumer consumer, MutableInt consumerSelectionCounter)
implements Comparable<ConsumerEntry> {
private static final Comparator<ConsumerEntry>
BASE_CONSUMER_ENTRY_COMPARATOR = Comparator.<ConsumerEntry, Integer>
comparing(entry -> entry.consumer().getPriorityLevel()).reversed()
.thenComparing(entry -> entry.consumer().consumerName());


private static final Comparator<ConsumerEntry>
CONSUMER_ENTRY_COMPARATOR = BASE_CONSUMER_ENTRY_COMPARATOR
// prefer the consumer instance with lowest selection count so that consumers get
// evenly distributed
.thenComparing(ConsumerEntry::consumerSelectionCounter);

@Override
public int compareTo(ConsumerEntry o) {
return CONSUMER_ENTRY_COMPARATOR.compare(this, o);
}

// comparison without the usage count so that the consumer doesn't get changed too eagerly
// when entries are removed
public int baseCompareTo(ConsumerEntry o) {
return BASE_CONSUMER_ENTRY_COMPARATOR.compare(this, o);
}
}

private final List<ConsumerEntry> consumers;
ConsumerEntry selectedConsumerEntry;

public HashRingEntry() {
this.consumers = new ArrayList<>();
}

public void addConsumer(Consumer consumer, MutableInt selectedCounter) {
consumers.add(new ConsumerEntry(consumer, selectedCounter));
selectConsumer(null);
}

public boolean removeConsumer(Consumer consumer) {
boolean removed = consumers.removeIf(consumerEntry -> consumerEntry.consumer().equals(consumer));
selectConsumer(consumer);
return removed;
}

public Consumer getSelectedConsumer() {
return selectedConsumerEntry != null ? selectedConsumerEntry.consumer() : null;
}

private void selectConsumer(Consumer removedConsumer) {
if (consumers.size() > 1) {
boolean addOperation = removedConsumer == null;
if (addOperation) {
Collections.sort(consumers);
}
ConsumerEntry newSelectedConsumer = consumers.get(0);
// change the selected consumer only if the newer has higher priority,
// or the same priority and an earlier name in sorting order
if (selectedConsumerEntry == null || addOperation
|| selectedConsumerEntry.consumer.equals(removedConsumer)
|| selectedConsumerEntry.baseCompareTo(newSelectedConsumer) > 0) {
changeSelectedConsumerEntry(newSelectedConsumer);
}
} else if (consumers.size() == 1) {
changeSelectedConsumerEntry(consumers.get(0));
} else {
changeSelectedConsumerEntry(null);
}
}

private void changeSelectedConsumerEntry(ConsumerEntry newSelectedConsumer) {
beforeChangingSelectedConsumerEntry();
selectedConsumerEntry = newSelectedConsumer;
afterChangingSelectedConsumerEntry();
}

private void beforeChangingSelectedConsumerEntry() {
if (selectedConsumerEntry != null) {
selectedConsumerEntry.consumerSelectionCounter.decrement();
}
}

private void afterChangingSelectedConsumerEntry() {
if (selectedConsumerEntry != null) {
selectedConsumerEntry.consumerSelectionCounter.increment();
}
}
}

@Override
public CompletableFuture<Void> addConsumer(Consumer consumer) {
rwLock.writeLock().lock();
Expand All @@ -61,24 +166,20 @@ public CompletableFuture<Void> addConsumer(Consumer consumer) {
// The points are deterministically added based on the hash of the consumer name
for (int i = 0; i < numberOfPoints; i++) {
int hash = calculateHashForConsumerAndIndex(consumer, i);
hashRing.compute(hash, (k, v) -> {
if (v == null) {
return Lists.newArrayList(consumer);
} else {
if (!v.contains(consumer)) {
v.add(consumer);
v.sort(Comparator.comparing(Consumer::consumerName, String::compareTo));
}
return v;
}
});
HashRingEntry hashRingEntry = hashRing.computeIfAbsent(hash, k -> new HashRingEntry());
// Add the consumer to the hash ring entry
hashRingEntry.addConsumer(consumer, getConsumerSelectedCount(consumer));
}
return CompletableFuture.completedFuture(null);
} finally {
rwLock.writeLock().unlock();
}
}

private MutableInt getConsumerSelectedCount(Consumer consumer) {
return consumerSelectionCounters.computeIfAbsent(consumer, k -> new MutableInt());
}

private static int calculateHashForConsumerAndIndex(Consumer consumer, int index) {
String key = consumer.consumerName() + KEY_SEPARATOR + index;
return Murmur3_32Hash.getInstance().makeHash(key.getBytes());
Expand All @@ -92,15 +193,11 @@ public void removeConsumer(Consumer consumer) {
for (int i = 0; i < numberOfPoints; i++) {
int hash = calculateHashForConsumerAndIndex(consumer, i);
hashRing.compute(hash, (k, v) -> {
if (v == null) {
return null;
} else {
v.removeIf(c -> c.equals(consumer));
if (v.isEmpty()) {
v = null;
}
return v;
v.removeConsumer(consumer);
if (v.getSelectedConsumer() == null) {
v = null;
}
return v;
});
}
} finally {
Expand All @@ -115,16 +212,14 @@ public Consumer select(int hash) {
if (hashRing.isEmpty()) {
return null;
}

List<Consumer> consumerList;
Map.Entry<Integer, List<Consumer>> ceilingEntry = hashRing.ceilingEntry(hash);
HashRingEntry hashRingEntry;
Map.Entry<Integer, HashRingEntry> ceilingEntry = hashRing.ceilingEntry(hash);
if (ceilingEntry != null) {
consumerList = ceilingEntry.getValue();
hashRingEntry = ceilingEntry.getValue();
} else {
consumerList = hashRing.firstEntry().getValue();
hashRingEntry = hashRing.firstEntry().getValue();
}

return consumerList.get(hash % consumerList.size());
return hashRingEntry.getSelectedConsumer();
} finally {
rwLock.readLock().unlock();
}
Expand All @@ -135,13 +230,24 @@ public Map<Consumer, List<Range>> getConsumerKeyHashRanges() {
Map<Consumer, List<Range>> result = new LinkedHashMap<>();
rwLock.readLock().lock();
try {
if (hashRing.isEmpty()) {
return result;
}
int start = 0;
for (Map.Entry<Integer, List<Consumer>> entry: hashRing.entrySet()) {
for (Consumer consumer: entry.getValue()) {
result.computeIfAbsent(consumer, key -> new ArrayList<>())
int lastKey = 0;
for (Map.Entry<Integer, HashRingEntry> entry: hashRing.entrySet()) {
Consumer consumer = entry.getValue().getSelectedConsumer();
result.computeIfAbsent(consumer, key -> new ArrayList<>())
.add(Range.of(start, entry.getKey()));
}
start = entry.getKey() + 1;
lastKey = entry.getKey();
start = lastKey + 1;
}
// Handle wrap-around
HashRingEntry firstHashRingEntry = hashRing.firstEntry().getValue();
Consumer firstSelectedConsumer = firstHashRingEntry.getSelectedConsumer();
List<Range> ranges = result.get(firstSelectedConsumer);
if (lastKey != Integer.MAX_VALUE - 1) {
ranges.add(Range.of(lastKey + 1, Integer.MAX_VALUE - 1));
}
} finally {
rwLock.readLock().unlock();
Expand Down
98 changes: 88 additions & 10 deletions ...java/org/apache/pulsar/broker/service/ConsistentHashingStickyKeyConsumerSelectorTest.java
View file
Original file line number Diff line number Diff line change
Expand Up @@ -18,9 +18,9 @@
*/
package org.apache.pulsar.broker.service;

import static org.assertj.core.api.Assertions.assertThat;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
Expand All @@ -31,6 +31,7 @@
import java.util.stream.IntStream;
import org.apache.pulsar.broker.service.BrokerServiceException.ConsumerAssignException;
import org.apache.pulsar.client.api.Range;
import org.mockito.Mockito;
import org.testng.Assert;
import org.testng.annotations.Test;

Expand All @@ -54,7 +55,7 @@ public void testConsumerSelect() throws ConsumerAssignException {
selector.addConsumer(consumer2);

final int N = 1000;
final double PERCENT_ERROR = 0.20; // 20 %
final double PERCENT_ERROR = 0.25; // 25 %

Map<String, Integer> selectionMap = new HashMap<>();
for (int i = 0; i < N; i++) {
Expand Down Expand Up @@ -146,12 +147,17 @@ public void testGetConsumerKeyHashRanges() throws BrokerServiceException.Consume
ConsistentHashingStickyKeyConsumerSelector selector = new ConsistentHashingStickyKeyConsumerSelector(3);
List<String> consumerName = Arrays.asList("consumer1", "consumer2", "consumer3");
List<Consumer> consumers = new ArrayList<>();
long id=0;
for (String s : consumerName) {
Consumer consumer = mock(Consumer.class);
when(consumer.consumerName()).thenReturn(s);
Consumer consumer = createMockConsumer(s, s, id++);
selector.addConsumer(consumer);
consumers.add(consumer);
}

// check that results are the same when called multiple times
assertThat(selector.getConsumerKeyHashRanges())
.containsExactlyEntriesOf(selector.getConsumerKeyHashRanges());

Map<Consumer, List<Range>> expectedResult = new HashMap<>();
expectedResult.put(consumers.get(0), Arrays.asList(
Range.of(119056335, 242013991),
Expand All @@ -160,17 +166,47 @@ public void testGetConsumerKeyHashRanges() throws BrokerServiceException.Consume
expectedResult.put(consumers.get(1), Arrays.asList(
Range.of(0, 90164503),
Range.of(90164504, 119056334),
Range.of(382436668, 722195656)));
Range.of(382436668, 722195656),
Range.of(1914695767, 2147483646)));
expectedResult.put(consumers.get(2), Arrays.asList(
Range.of(242013992, 242377547),
Range.of(242377548, 382436667),
Range.of(1656011843, 1707482097)));
for (Map.Entry<Consumer, List<Range>> entry : selector.getConsumerKeyHashRanges().entrySet()) {
System.out.println(entry.getValue());
Assert.assertEquals(entry.getValue(), expectedResult.get(entry.getKey()));
expectedResult.remove(entry.getKey());
assertThat(selector.getConsumerKeyHashRanges()).containsExactlyInAnyOrderEntriesOf(expectedResult);
}

@Test
public void testConsumersGetEvenlyMappedWhenThereAreCollisions()
throws BrokerServiceException.ConsumerAssignException {
ConsistentHashingStickyKeyConsumerSelector selector = new ConsistentHashingStickyKeyConsumerSelector(5);
List<Consumer> consumers = new ArrayList<>();
for (int i = 0; i < 5; i++) {
// use the same name for all consumers
Consumer consumer = createMockConsumer("consumer", "index " + i, i);
selector.addConsumer(consumer);
consumers.add(consumer);
}
Assert.assertEquals(expectedResult.size(), 0);
// check that results are the same when called multiple times
assertThat(selector.getConsumerKeyHashRanges())
.containsExactlyEntriesOf(selector.getConsumerKeyHashRanges());

Map<Consumer, List<Range>> expectedResult = new HashMap<>();
expectedResult.put(consumers.get(0), List.of(Range.of(306176209, 365902830)));
expectedResult.put(consumers.get(1), List.of(Range.of(216056714, 306176208)));
expectedResult.put(consumers.get(2), List.of(Range.of(365902831, 1240826377)));
expectedResult.put(consumers.get(3), List.of(Range.of(1240826378, 1862045174)));
expectedResult.put(consumers.get(4), List.of(Range.of(0, 216056713), Range.of(1862045175, 2147483646)));
assertThat(selector.getConsumerKeyHashRanges()).containsExactlyInAnyOrderEntriesOf(expectedResult);
}

private static Consumer createMockConsumer(String consumerName, String toString, long id) {
// without stubOnly, the mock will record method invocations and run into OOME
Consumer consumer = mock(Consumer.class, Mockito.withSettings().stubOnly());
when(consumer.consumerName()).thenReturn(consumerName);
when(consumer.getPriorityLevel()).thenReturn(0);
when(consumer.toString()).thenReturn(toString);
when(consumer.consumerId()).thenReturn(id);
return consumer;
}

// reproduces https://github.com/apache/pulsar/issues/22050
Expand Down Expand Up @@ -216,4 +252,46 @@ public void shouldRemoveConsumersFromConsumerKeyHashRanges() {
// then there should be no mapping remaining
Assert.assertEquals(selector.getConsumerKeyHashRanges().size(), 0);
}

@Test
public void testShouldNotChangeSelectedConsumerWhenConsumerIsRemoved() {
final ConsistentHashingStickyKeyConsumerSelector selector = new ConsistentHashingStickyKeyConsumerSelector(25);
final String consumerName = "consumer";
final int numOfInitialConsumers = 25;
List<Consumer> consumers = new ArrayList<>();
for (int i = 0; i < numOfInitialConsumers; i++) {
final Consumer consumer = createMockConsumer(consumerName, "index " + i, i);
consumers.add(consumer);
selector.addConsumer(consumer);
}

int hashRangeSize = Integer.MAX_VALUE;
int validationPointCount = 100;
int increment = hashRangeSize / validationPointCount;
List<Consumer> selectedConsumerBeforeRemoval = new ArrayList<>();

for (int i = 0; i < validationPointCount; i++) {
selectedConsumerBeforeRemoval.add(selector.select(i * increment));
}

for (int i = 0; i < validationPointCount; i++) {
Consumer selected = selector.select(i * increment);
Consumer expected = selectedConsumerBeforeRemoval.get(i);
assertThat(selected.consumerId()).as("validationPoint %d", i).isEqualTo(expected.consumerId());
}

/*
TODO: failing test case
for (Consumer removedConsumer : consumers) {
selector.removeConsumer(removedConsumer);
for (int i = 0; i < validationPointCount; i++) {
Consumer selected = selector.select(i * increment);
Consumer expected = selectedConsumerBeforeRemoval.get(i);
if (expected != removedConsumer) {
assertThat(selected.consumerId()).as("validationPoint %d", i).isEqualTo(expected.consumerId());
}
}
}
*/
}
}

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