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new 17a9d2d4546 [feature][blog] Add 2.9.3 release blog (#16772)
17a9d2d4546 is described below
commit 17a9d2d45462eee682f1eba29bb2584f211eb1fb
Author: momo-jun <[email protected]>
AuthorDate: Fri Jul 29 10:35:19 2022 +0800
[feature][blog] Add 2.9.3 release blog (#16772)
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+---
+title: "What’s New in Apache Pulsar 2.9.3"
+date: 2022-07-27
+author: "mattisonchao, momo-jun"
+---
+
+The Apache Pulsar community releases version 2.9.3! 50 contributors provided
improvements and bug fixes that delivered 200+ commits. Thanks for all your
contributions.
+
+The highlight of the 2.9.3 release is introducing 30+ transaction fixes and
improvements. Earlier-adoption users of Pulsar transactions have documented
long-term use in their production environments and reported valuable findings
in real applications. This provides the Pulsar community with the opportunity
to make a difference.
+
+This blog walks through the most noteworthy changes. For the complete list
including all feature enhancements and bug fixes, check out the [Pulsar 2.9.3
Release Notes](https://pulsar.apache.org/release-notes/versioned/pulsar-2.9.3/).
+
+
+### Enabled cursor data compression to reduce persistent cursor data size.
[14542](https://github.com/apache/pulsar/pull/14542)
+
+#### Issue
+The cursor data is managed by the ZooKeeper/Etcd metadata store. When the data
size increases, it may take too much time to pull the data, and brokers may end
up writing large chunks of data to the ZooKeeper/Etcd metadata store.
+
+#### Resolution
+Provide the ability to enable compression mechanisms to reduce cursor data
size and the pulling time.
+
+
+### Reduced the memory occupied by `metadataPositions` and avoid OOM.
[15137](https://github.com/apache/pulsar/pull/15137)
+
+#### Issue
+The map `metadataPositions` in MLPendingAckStore is used to clear useless data
in PendingAck, where the key is the position that is persistent in PendingAck
and the value is the max position acked by an operation. It judges whether the
max subscription cursor position is smaller than the subscription cursor’s
`markDeletePosition`. If the max position is smaller, then the log cursor will
mark to delete the position. It causes two main issues:
+* In normal cases, this map stores all transaction ack operations. This is a
waste of memory and CPU.
+* If a transaction that has not been committed for a long time acks a message
in a later position, the map will not be cleaned up, which finally leads to OOM
(out-of-memory).
+
+#### Resolution
+Regularly store a small amount of data according to certain rules. For more
detailed implementation, refer to
[PIP-153](https://github.com/apache/pulsar/issues/15073).
+
+
+### Checked `lowWaterMark` before appending transaction entries to Transaction
Buffer. [15424](https://github.com/apache/pulsar/pull/15424)
+
+#### Issue
+When a client sends messages using a previously committed transaction, these
messages are visible to consumers unexpectedly.
+
+#### Resolution
+Add a map to store the `lowWaterMark` of Transaction Coordinator in
Trasanction Buffer, and check `lowWaterMark` before appending transaction
entries to Trasanction Buffer. So when sending messages using an invalid
transaction, clients will receive `NotAllowedException`.
+
+
+### Fixed the consumption performance regression.
[PR-15162](https://github.com/apache/pulsar/pull/15162)
+
+#### Issue
+This performance regression was introduced in 2.10.0, 2.9.1, and 2.8.3. You
may find a significant performance drop with message listeners while using Java
Client. The root cause is each message will introduce the thread switching from
the external thread pool to the internal thread poll and then to the external
thread pool.
+
+#### Resolution
+Avoid the thread switching for each message to improve consumption throughput.
+
+
+### Fixed a deadlock issue of topic creation.
[PR-15570](https://github.com/apache/pulsar/pull/15570)
+
+#### Issue
+This deadlock issue occurred during topic creation by trying to re-acquire the
same `StampedLock` from the same thread when removing it. This will cause the
topic to stop service for a long time, and ultimately with a failure in the
deduplication or geo-replication check. The workaround is restarting the broker.
+
+
+### Optimized the memory usage of brokers.
+
+#### Issue
+Pulsar has some internal data structures, such as
`ConcurrentLongLongPairHashMap`, and `ConcurrentLongPairHashMap`, which can
reduce the memory usage rather than using the Boxing type. However, in earlier
versions, the data structures were not supported for shrinking even if the data
was removed, which wasted a certain amount of memory in certain situations.
+
+**Pull requests**
+* https://github.com/apache/pulsar/pull/15354
+* https://github.com/apache/pulsar/pull/15342
+* https://github.com/apache/pulsar/pull/14663
+* https://github.com/apache/pulsar/pull/14515
+* https://github.com/apache/pulsar/pull/14497
+
+#### Resolution
+Support the shrinking of the internal data structures, such as
`ConcurrentSortedLongPairSet`, `ConcurrentOpenHashMap`, and so on.
+
+
+# What’s Next?
+
+If you are interested in learning more about Pulsar 2.9.3, you can
[download](https://pulsar.apache.org/versions/) and try it out now!
+
+**Pulsar Summit San Francisco 2022** will take place on August 18th, 2022.
[Register now](https://pulsar-summit.org/) 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 current progress,
visit
+the [Pulsar website](https://pulsar.apache.org), follow the project on Twitter
+[@apache_pulsar](https://twitter.com/apache_pulsar), and join [Pulsar
Slack](https://apache-pulsar.herokuapp.com/)!
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