Hi Christo, I'll leave Kirk to explain the impact properly. It is not a regression in 4.2 and looks like the problem has existed for a while.
We have bug fix releases for several Kafka versions running at the moment. Personally, I'd like a fix for this in 4.1.2 because there might not be a 4.1.3. For 4.2.0, we know there will be a 4.2.1, so we do have an easy way of making a fix available in the 4.2.x line. Whether it's considered a blocker for 4.2.0 or not, we can ship a fix in a timely manner. Thanks, Andrew On 2026/02/11 08:50:58 Christo Lolov wrote: > Hello Kirk, > > Thanks for bringing this to my attention! Could you help me understand the > impact of this? As far as I understand the description, the downside is > that if a consumer runs into this it will no longer report an accurate lag > metric. If this is the only impact I am inclined to err on the side of not > considering it a blocker for 4.2.0, calling it out in the blog post and > including it in 4.2.1. > > Thoughts? > > Best, > Christo > > On Tue, 10 Feb 2026 at 19:24, Kirk True <[email protected]> wrote: > > > Hi Christo, > > > > We recently discovered KAFKA-20131 which, although not a regression, can > > cause the Consumer.currentLag() API call to be unable to fetch the lag > > until the Consumer is closed and another is restarted. There's been a > > couple of off-mailing list discussions about this, but wanted to raise it > > as a potential blocker here for broader discussion. > > > > Thanks, > > Kirk > > > > On Tue, Feb 10, 2026, at 7:27 AM, Christo Lolov wrote: > > > Hello Kafka users, developers and client-developers, > > > > > > This is the RC4 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-rc4/RELEASE_NOTES.html > > > > > > *** Please download, test and vote by Friday, February 13, 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-rc4/ > > > > > > * Docker release artifacts to be voted upon: > > > apache/kafka:4.2.0-rc4 > > > apache/kafka-native:4.2.0-rc4 > > > > > > * 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-rc4/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-rc4 > > > > > > * 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/21860071096 > > > 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/21861574007 > > > Docker Build Test Pipeline (Native): > > > https://github.com/apache/kafka/actions/runs/21861786570 > > > > > > Thanks, > > > Christo > > > > > >
