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https://issues.apache.org/jira/browse/KAFKA-6607?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matthias J. Sax resolved KAFKA-6607.
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Fix Version/s: 2.5.0
Resolution: Fixed
> Kafka Streams lag not zero when input topic transactional
> ---------------------------------------------------------
>
> Key: KAFKA-6607
> URL: https://issues.apache.org/jira/browse/KAFKA-6607
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 1.0.0
> Reporter: Matthias J. Sax
> Assignee: Matthias J. Sax
> Priority: Minor
> Fix For: 2.5.0
>
>
> When an input topic for a Kafka Streams application is written using
> transaction, Kafka Streams commits an "incorrect" offset, ie, it commits
> "lastProcessedMessageOffset + 1" that is smaller than "endOffset" if it
> reaches the end of topic. The reason is the commit marker that is the last
> "message" in the topic; Streams does not take commit markers into account
> when committing.
> This is not a correctness issue, but when one inspect the consumer lag via
> {{bin/kafka-consumer.group.sh}} the lag is shown as 1 instead of 0 – what is
> correct from consumer-group tool point of view.
> Note that all applications using a plain consumer may face the same issue if
> they use `KafkaConsumer#commitSync(Map<TopicPartition, OffsetAndMetadata>
> offsets)`: to address the issue, the correct pattern is to either commit
> "nextRecord.offset()" (if the next record is available already, ie, was
> returned by `poll()`, or use `consumer.position()` that takes the commit
> marker into account and would "step over it").
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