Sep 23, 2021
10 min read

What’s New in Apache Pulsar 2.8.1

Yu Liu
Hang Chen
Software Engineer, StreamNative & Apache Pulsar PMC Member

What’s New in Apache Pulsar 2.8.1

The Apache Pulsar community releases version 2.8.1! 49 contributors provided improvements and bug fixes that delivered 213 commits.

Highlights of this release are as below:

  • Key-shared subscriptions no longer stop dispatching to consumers when repeatedly opening and closing consumers. PR-10920
  • System topic no longer has potential data loss when not configured for compaction. PR-11003
  • Consumers are not allowed to read data on topics to which they are not subscribed. PR-11912

This blog walks through the most noteworthy changes grouped by component. For the complete list including all features, enhancements, and bug fixes, check out the Pulsar 2.8.1 Release Notes.

Notable bug fixes and enhancements


Precise publish rate limit takes effect as expected. PR-11446

Issue: Previously, when setting precise publish rate limits on topics, it did not work.

Resolution: Implemented a new RateLimiter using the LeakingBucket and FixedWindow algorithms.

Messages with the same keys are delivered to the correct consumers on Key-Shared subscriptions. PR-10762

Issue: Messages with the same keys were out of order when message redelivery occurred on a Key-Shared subscription.

Resolution: When sending a message to messagesToRedeliver, the broker saved the hash value of the key. If the dispatcher attempted to send newer messages to the consumer that had a key corresponding to any one of the saved hash values, they were added to messagesToRedeliver instead of being sent. This prevented messages with the same key from being out of order.

Active producers with the same name are no longer removed from the topic map. PR-11804

Issue: Previously, when there were producers with the same name, an error would be triggered and the old producer would be removed even though it was still writing to a topic.

Resolution: Validated producers based on a connection ID (local & remote addresses and unique ID) and a producer ID within that connection rather than a producer name.

Topics in a fenced state can recover when producers continue to reconnect to brokers. PR-11737

Issue: Previously, when a producer continued to reconnect to a broker, the fenced state of the topic was always set to true, which caused the topic to be unable to recover.

Resolution: Add an entry to ManagedLedgerException when the polled operation is not equal to the current operation.

Topic properly initializes the cursor to prevent data loss. PR-11547

Issue: Previously, when subscribing to a topic with the earliest position, data would be lost because ManagedLedger used a wrong position to initialize a cursor.

Resolution: Added a test to check a cursor's position when subscribing to a topic with the earliest position.

Deadlock no longer occurs when using hasMessageAvailableAsync and readNextAsync. PR-11183

Issue: Previously, when messages were added to an incoming queue, a deadlock might occur. The deadlock might happen in two possible scenarios. First, if the message was added to the queue before the message was read. Second, if readNextAsync was completed before future.whenComplete was called.

Resolution: Used an internal thread to process the callback of hasMessageAvailableAsync.

Memory leak does not occur when calling getLastMessageId API. PR-10977

Issue: Previously, the broker ran out of memory when calling the getLastMessageId API.

Resolution: Added the entry.release() call to the PersistentTopic.getLastMessageId.

Compaction is triggered for system topics. PR-10941

Issue: Previously, when a topic had only non-durable subscriptions, the compaction was not triggered because it had 0 estimated backlog size.

Resolution: Used the total backlog size to trigger the compaction. Changed the behavior in the case of no durable subscriptions to use the total backlog size

Key-shared subscriptions no longer stop dispatching to consumers when repeatedly opening and closing consumers. PR-10920

Issue: Repeatedly opening and closing consumers with a Key-Shared subscription might occasionally stop dispatching messages to all consumers.

Resolution: Moved the mark-delete position and removed the consumer from the selector before calling removeConsumer().

Consumers are not allowed to read data on topics to which they are not subscribed. PR-11912

Issue: Previously, the request ledger was not checked whether it belonged to a consumer’s connected topic, which allowed the consumer to read data that does not belong to the connected topic.

Resolution: Added a check on the ManagedLedger level before executing read operations.

Topic Policy

Retention policy works as expected. PR-11021

Issue: Previously, the retention policy did not work because it was not set in the managedLedger configuration.

Resolution: Set the retention policy in the managedLedger configuration to the onUpdate listener method.

System topic no longer has potential data loss when not configured for compaction. PR-11003

Issue: Previously, data might be lost if there were no durable subscriptions on topics.

Resolution: Leveraged the topic compaction cursor to retain data.


Pulsar proxy correctly shuts down outbound connections. PR-11848

Issue: Previously, there was a memory leak of outgoing TCP connections in the Pulsar proxy because the ProxyConnectionPool instances were created outside the PulsarClientImpl instance and not closed when the client was closed.

Resolution: Shut down the ConnectionPool correctly.


Pulsar Functions support Protobuf schema. PR-11709

Issue: Previously, the exception GeneratedMessageV3 is not assignable was thrown when using a Protobuf schema.

Resolution: Added the relevant dependencies to the Pulsar instance.


Partitioned-topic consumers clean up resources after a failure. PR-11754

Issue: Previously, partitioned-topic consumers did not clean up the resources when failing to create consumers. If this failure occurred with non-recoverable errors, it triggered a memory leak, which made applications unstable.

Resolution: Closed and cleaned timer task references.

Race conditions do not occur on multi-topic consumers. PR-11764

Issue: Previously, there was a race condition between 2 threads when one of the individual consumers was in a "paused" state and the shared queue was full.

Resolution: Validated the state of the shared queue after marking the consumer as "paused". The consumer is not blocked if the other thread has emptied the queue in the meantime.

Consumers are not blocked on batchReceive. PR-11691

Issue: Previously, consumers were blocked when Consumer.batchReceive() was called concurrently by different threads due to a race condition in

Resolution: Put pinnedInternalExecutor in ConsumerBase to allow batch timer, ConsumerImpl, and MultiTopicsConsumerImpl to submit work in a single thread.

Python client correctly enables custom logging. PR-11882

Issue: Previously, deadlock might happen when custom logging was enabled in the Python client.

Resolution: Detached the worker thread and reduced log level.

What is Next?

If you are interested in learning more about Pulsar 2.8.1, you can download and try it out now!

The first-ever Pulsar Virtual Summit Europe 2021 will take place in October. Register now and help us make it an even bigger success by spreading the word on social media!

For more information about the Apache Pulsar project and the progress, visit the Pulsar website, follow the project on Twitter @apache_pulsar, and join Pulsar Slack!

Get involved

To get started, you can download Pulsar directly or you can spin up a Pulsar cluster with a free 30-day trial of StreamNative Cloud! We also offer technical consulting and expert training to help get your organization started. As always, we are highly responsive to your feedback. Feel free to contact us if you have any questions at any time. We look forward to hearing from you and stay tuned for the next Pulsar release!

Yu Liu
Yu Liu is an Apache Pulsar PMC member and a content strategist from StreamNative.
Hang Chen
Hang Chen is an Apache Pulsar PMC member and a software engineer at StreamNative. He once worked at BIGO, a Singapore-based technology company that provides video-based social media products. He mainly focuses on Pulsar stability, performance, Flink integration, and KoP.


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