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[Enhancement] Optimize delayed message delivery by reducing unnecessary reads to storage in InMemoryDelayedDeliveryTracker #23912

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#23918
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[Enhancement] Optimize delayed message delivery by reducing unnecessary reads to storage in InMemoryDelayedDeliveryTracker#23912
#23918
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type/enhancementThe enhancements for the existing features or docs. e.g. reduce memory usage of the delayed messages
@lhotari

Description

@lhotari
lhotari
opened on Jan 30, 2025

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Motivation

In the current delayed message delivery, there's an opportunity to reduce unnecessary reads to storage.

In Pulsar, there are 2 implementations for the delayed delivery tracker, InMemoryDelayedDeliveryTracker and BucketDelayedDeliveryTracker.
This is configured by the delayedDeliveryTrackerFactoryClassName configuration key. The default setting chooses the in memory implementation:

pulsar/conf/broker.conf

Lines 614 to 617 in b02d52c

# Class name of the factory that implements the delayed deliver tracker.
# If value is "org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTrackerFactory",
# will create bucket based delayed message index tracker.
delayedDeliveryTrackerFactoryClassName=org.apache.pulsar.broker.delayed.InMemoryDelayedDeliveryTrackerFactory

The BucketDelayedDeliveryTracker contains an optimization to skip messages in reading which have been "indexed":

pulsar/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentDispatcherMultipleConsumers.java

Lines 446 to 457 in 11a615e

protected Predicate<Position> createReadEntriesSkipConditionForNormalRead() {
Predicate<Position> skipCondition = null;
// Filter out and skip read delayed messages exist in DelayedDeliveryTracker
if (delayedDeliveryTracker.isPresent()) {
final DelayedDeliveryTracker deliveryTracker = delayedDeliveryTracker.get();
if (deliveryTracker instanceof BucketDelayedDeliveryTracker) {
skipCondition = position -> ((BucketDelayedDeliveryTracker) deliveryTracker)
.containsMessage(position.getLedgerId(), position.getEntryId());
}
}
return skipCondition;
}

This already reduces reads when BucketDelayedDeliveryTracker is in use.

The state of the InMemoryDelayedDeliveryTracker gets cleared after all consumers have disconnected:

pulsar/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentDispatcherMultipleConsumers.java

Lines 187 to 202 in 12b0579

if (consumerList.isEmpty()) {
if (havePendingRead || havePendingReplayRead) {
// There is a pending read from previous run. We must wait for it to complete and then rewind
shouldRewindBeforeReadingOrReplaying = true;
} else {
cursor.rewind();
shouldRewindBeforeReadingOrReplaying = false;
}
redeliveryMessages.clear();
delayedDeliveryTracker.ifPresent(tracker -> {
// Don't clean up BucketDelayedDeliveryTracker, otherwise we will lose the bucket snapshot
if (tracker instanceof InMemoryDelayedDeliveryTracker) {
tracker.clear();
}
});
}

Solution

It would be useful to keep state also in the InMemoryDelayedDeliveryTracker and skip reading delayed messages when the information is already available for the delivery time of a specific entry.

Alternatives

No response

Anything else?

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Are you willing to submit a PR?

  • I'm willing to submit a PR!

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