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[Subscription] Prevent consumers from idling on dry regions #18738

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Merged
jt2594838 merged 2 commits into from
Sep 30, 2026
Merged

[Subscription] Prevent consumers from idling on dry regions #18738

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fbb8227
[Subscription] Prevent consumers from idling on dry regions
Caideyipi Sep 28, 2026
0167f1f
Merge origin/master into fix/subscription-dry-region-polling-master
Caideyipi Sep 30, 2026
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37 changes: 31 additions & 6 deletions ...de/src/main/java/org/apache/iotdb/db/subscription/broker/ConsensusSubscriptionBroker.java
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Original file line number Diff line number Diff line change
Expand Up @@ -140,15 +140,25 @@ public List<SubscriptionEvent> poll(
refreshAndGetTopicOwnership(topicName, queues, consumerId);
final List<ConsensusPrefetchingQueue> assignedQueues =
getAssignedQueues(queues, consumerId, ownershipSnapshot);
if (assignedQueues.isEmpty()) {
final List<ConsensusPrefetchingQueue> pollQueues =
new ArrayList<>(buildPollOrderForAssignedQueues(assignedQueues, topicName));
final int assignedQueueCount = pollQueues.size();
pollQueues.addAll(buildFallbackPollOrder(queues, assignedQueues));
if (pollQueues.isEmpty()) {
continue;
}

final List<ConsensusPrefetchingQueue> pollQueues =
buildPollOrderForAssignedQueues(assignedQueues, topicName);
final int eventsBeforeTopicPoll = eventsToPoll.size();

for (final ConsensusPrefetchingQueue consensusQueue : pollQueues) {
for (int queueIndex = 0; queueIndex < pollQueues.size(); queueIndex++) {
final boolean isFallbackQueue = queueIndex >= assignedQueueCount;
// Ownership remains the preferred polling path. Only borrow one ready event from another
// region when every assigned region is currently empty, preventing a consumer from timing
// out solely because its region has a temporary dry spell.
if (isFallbackQueue && eventsToPoll.size() > eventsBeforeTopicPoll) {
break;
}

final ConsensusPrefetchingQueue consensusQueue = pollQueues.get(queueIndex);
if (consensusQueue.isClosed()) {
continue;
}
Expand Down Expand Up @@ -185,7 +195,7 @@ public List<SubscriptionEvent> poll(
eventsToPoll.add(event);
totalSize += currentSize;

if (totalSize >= maxBytes) {
if (isFallbackQueue || totalSize >= maxBytes) {
break;
}
}
Expand Down Expand Up @@ -616,6 +626,21 @@ private List<ConsensusPrefetchingQueue> buildPollOrderForAssignedQueues(
return orderedQueues;
}

private List<ConsensusPrefetchingQueue> buildFallbackPollOrder(
final List<ConsensusPrefetchingQueue> queues,
final List<ConsensusPrefetchingQueue> assignedQueues) {
return queues.stream()
.filter(queue -> !queue.isClosed())
.filter(queue -> !assignedQueues.contains(queue))
// Do not block on another consumer's region. Borrow only events that are already ready.
.filter(queue -> queue.getPrefetchedEventCount() > 0)
.sorted(
Comparator.comparingLong(ConsensusPrefetchingQueue::getLag)
.reversed()
.thenComparing(queue -> queue.getConsensusGroupId().toString()))
.collect(Collectors.toList());
}

private ConsensusPrefetchingQueue getQueueForCommitContext(
final List<ConsensusPrefetchingQueue> queues, final SubscriptionCommitContext commitContext) {
final String regionId = commitContext.getRegionId();
Expand Down
53 changes: 53 additions & 0 deletions .../org/apache/iotdb/db/subscription/broker/ConsensusSubscriptionBrokerPayloadLimitTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -35,13 +35,15 @@
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertSame;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.never;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

public class ConsensusSubscriptionBrokerPayloadLimitTest {

private static final String CONSUMER_GROUP_ID = "consumerGroup";
private static final String CONSUMER_ID = "consumer";
private static final String OTHER_CONSUMER_ID = "otherConsumer";
private static final String TOPIC_NAME = "topic";

@Test
Expand Down Expand Up @@ -73,6 +75,57 @@ public void testPollRequeuesEventThatWouldExceedPayloadLimit() throws Exception
verify(secondQueue).requeue(CONSUMER_ID, secondCommitContext);
}

@Test
public void testPollBorrowsReadyEventWhenAssignedQueueIsEmpty() throws Exception {
final ConsensusSubscriptionBroker broker = new ConsensusSubscriptionBroker(CONSUMER_GROUP_ID);
final ConsensusPrefetchingQueue fallbackQueue = mock(ConsensusPrefetchingQueue.class);
final ConsensusPrefetchingQueue assignedQueue = mock(ConsensusPrefetchingQueue.class);
final SubscriptionEvent fallbackEvent = mock(SubscriptionEvent.class);

when(fallbackQueue.getConsensusGroupId()).thenReturn(new DataRegionId(1));
when(assignedQueue.getConsensusGroupId()).thenReturn(new DataRegionId(2));
when(fallbackQueue.getPrefetchedEventCount()).thenReturn(1);
when(fallbackQueue.poll(CONSUMER_ID, null)).thenReturn(fallbackEvent);
when(fallbackEvent.getCurrentResponseSize()).thenReturn(30);
bindQueues(broker, Arrays.asList(fallbackQueue, assignedQueue));

// The first consumer initially owns both regions. After the second consumer joins, the stable
// ownership balancer moves DataRegion[2] to it and keeps DataRegion[1] with the first consumer.
broker.poll(OTHER_CONSUMER_ID, Collections.singleton(TOPIC_NAME), 60L);
final List<SubscriptionEvent> events =
broker.poll(CONSUMER_ID, Collections.singleton(TOPIC_NAME), 60L);

assertEquals(1, events.size());
assertSame(fallbackEvent, events.get(0));
verify(assignedQueue).poll(CONSUMER_ID, null);
verify(fallbackQueue).poll(CONSUMER_ID, null);
}

@Test
public void testPollKeepsOwnershipAffinityWhenAssignedQueueHasData() throws Exception {
final ConsensusSubscriptionBroker broker = new ConsensusSubscriptionBroker(CONSUMER_GROUP_ID);
final ConsensusPrefetchingQueue fallbackQueue = mock(ConsensusPrefetchingQueue.class);
final ConsensusPrefetchingQueue assignedQueue = mock(ConsensusPrefetchingQueue.class);
final SubscriptionEvent fallbackEvent = mock(SubscriptionEvent.class);
final SubscriptionEvent assignedEvent = mock(SubscriptionEvent.class);

when(fallbackQueue.getConsensusGroupId()).thenReturn(new DataRegionId(1));
when(assignedQueue.getConsensusGroupId()).thenReturn(new DataRegionId(2));
when(fallbackQueue.getPrefetchedEventCount()).thenReturn(1);
when(fallbackQueue.poll(CONSUMER_ID, null)).thenReturn(fallbackEvent);
when(assignedQueue.poll(CONSUMER_ID, null)).thenReturn(assignedEvent);
when(assignedEvent.getCurrentResponseSize()).thenReturn(30);
bindQueues(broker, Arrays.asList(fallbackQueue, assignedQueue));

broker.poll(OTHER_CONSUMER_ID, Collections.singleton(TOPIC_NAME), 60L);
final List<SubscriptionEvent> events =
broker.poll(CONSUMER_ID, Collections.singleton(TOPIC_NAME), 60L);

assertEquals(1, events.size());
assertSame(assignedEvent, events.get(0));
verify(fallbackQueue, never()).poll(CONSUMER_ID, null);
}

@Test
public void testRequeueInFlightEventsAcrossRegionQueues() throws Exception {
final ConsensusSubscriptionBroker broker = new ConsensusSubscriptionBroker(CONSUMER_GROUP_ID);
Expand Down
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