Hey all, While I agree that KAFKA-20115 is not a regression in 4.2, I think that releasing 4.2 without the fix would be really bad as it impacts all groups using the classic protocol. They experience long rebalances when the underlying __consumer_offsets hosting them is reassigned in the cluster, which is common with tools such as Cruise Control. It is pretty disruptive.
Best, David On Sun, Feb 8, 2026 at 12:32 PM Christo Lolov <[email protected]> wrote: > Hello Mickael, > > In my opinion KAFKA-20115 is a blocker and necessitates another RC once > merged. My hope is that one will be the last RC for 4.2.0. Let me know if > you disagree with the classification. > > Hello Matthias, > > Before I prepare a new RC, I will cherry-pick the changes. > > Best, > Christo > > > On 7 Feb 2026, at 00:03, Matthias J. Sax <[email protected]> wrote: > > > > Hello, > > > > If we do a new RC, can we merge and cherry-pick two minor docs PRs? > > > > - https://github.com/apache/kafka/pull/21366 > > - https://github.com/apache/kafka/pull/21397 > > > > Both already approved -- did just hold off to merge to `trunk`, to not > later forget to do the cherry-pick. > > > > > > I also just approved a bug-fix for > https://issues.apache.org/jira/browse/KAFKA-19960 ( > https://github.com/apache/kafka/pull/21365) which is a critical bug. Also > ok to only get into 4.2.1, but of course better to get into 4.2.0 directly > if there is no objection? > > > > > > -Matthias > > > > > >> On 2/6/26 6:59 AM, Mickael Maison wrote: > >> Hi Christo, > >> Can you clarify how you've triaged > >> https://issues.apache.org/jira/browse/KAFKA-20115? > >> Is it a regression that requires a new RC or not? > >> Thanks, > >> Mickael > >>> On Tue, Feb 3, 2026 at 7:00 PM Sean Quah via dev <[email protected]> > wrote: > >>> > >>> Hi all, > >>> Unfortunately we discovered a regression in 4.2 today: > >>> https://issues.apache.org/jira/browse/KAFKA-20115 > >>> The impact is that when we have a group coordinator leadership change > in > >>> the middle of consumer group rebalancing, we can leave parked > JoinGroup and > >>> SyncGroup requests hanging until clients time out the request. I think > the > >>> timeout interval is the rebalance timeout/max.poll.interval.ms which > is 5 > >>> minutes long by default, so it can be fairly disruptive to consumer > >>> applications. > >>> > >>> A fix is in progress at https://github.com/apache/kafka/pull/21396. > >>> > >>> Thanks, > >>> Sean > >>> > >>>> On Mon, Feb 2, 2026 at 4:42 PM Christo Lolov <[email protected]> > wrote: > >>> > >>>> Hello Kafka users, developers and client-developers, > >>>> > >>>> This is the RC3 candidate for release of Apache Kafka 4.2.0. > >>>> > >>>> This release has many exciting changes: > >>>> * Kafka Queues (Share Groups) is now production-ready with new > >>>> features like the RENEW acknowledgement type for extended processing > >>>> times, adaptive batching for coordinators, and comprehensive lag > >>>> metrics. > >>>> * Kafka Streams brings the server-side rebalance protocol to GA with a > >>>> limited feature set, adds dead letter queue support in exception > >>>> handlers, introduces anchored wall-clock punctuation for deterministic > >>>> scheduling, and gives users full control over whether to send a leave > >>>> group request on closing. > >>>> * This release also delivers significant improvements to consistency > >>>> and observability: CLI tools now feature standardized arguments like > >>>> --bootstrap-server across all tools, metric naming has been corrected > >>>> to follow the kafka.COMPONENT convention, and new idle ratio metrics > >>>> provide better visibility into controller and MetadataLoader > >>>> performance. > >>>> * Security is enhanced with a new allowlist connector client > >>>> configuration override policy, while thread-safety improvements to > >>>> RecordHeader eliminate concurrency risks. > >>>> * Additional highlights include external schema support in > >>>> JsonConverter for reduced message sizes, dynamic configuration for > >>>> remote log manager thread pools, and rack ID exposure in the Admin API > >>>> for consumer and share group members. > >>>> > >>>> Release notes for the 4.2.0 release: > >>>> > https://dist.apache.org/repos/dist/dev/kafka/4.2.0-rc3/RELEASE_NOTES.html > >>>> > >>>> *** Please download, test and vote by Thursday, February 5, 5pm UTC > >>>> > >>>> Kafka's KEYS file containing PGP keys we use to sign the release: > >>>> https://kafka.apache.org/KEYS > >>>> > >>>> * Release artifacts to be voted upon (source and binary): > >>>> https://dist.apache.org/repos/dist/dev/kafka/4.2.0-rc3/ > >>>> > >>>> * Docker release artifacts to be voted upon: > >>>> apache/kafka:4.2.0-rc3 > >>>> apache/kafka-native:4.2.0-rc3 > >>>> > >>>> * Maven artifacts to be voted upon: > >>>> > https://repository.apache.org/content/groups/staging/org/apache/kafka/ > >>>> > >>>> * Javadoc: > >>>> > https://dist.apache.org/repos/dist/dev/kafka/4.2.0-rc3/javadoc/index.html > >>>> > >>>> * Tag to be voted upon (off 4.2 branch) is the 4.2.0 tag: > >>>> https://github.com/apache/kafka/releases/tag/4.2.0-rc3 > >>>> > >>>> * Documentation: > >>>> * Protocol: > >>>> https://github.com/apache/kafka-site/pull/785 > >>>> > >>>> * Successful CI builds for the 4.2 branch: > >>>> Unit/integration tests: > >>>> https://github.com/apache/kafka/actions/runs/21591368372 > >>>> System tests: I have started the tests in my environment and will > share > >>>> test > >>>> results in the next ~24 hours. > >>>> > >>>> * Successful Docker Image Github Actions Pipeline for 4.2 branch: > >>>> Docker Build Test Pipeline (JVM): > >>>> https://github.com/apache/kafka/actions/runs/21591979775 > >>>> Docker Build Test Pipeline (Native): > >>>> https://github.com/apache/kafka/actions/runs/21592431252 > >>>> > >>>> Thanks, > >>>> Christo > >>>> > > >
