Edoardo Comar created KAFKA-16622:
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             Summary: Mirromaker2 first Checkpoint not emitted until consumer 
group fully catches up once
                 Key: KAFKA-16622
                 URL: https://issues.apache.org/jira/browse/KAFKA-16622
             Project: Kafka
          Issue Type: Bug
          Components: mirrormaker
    Affects Versions: 3.6.2, 3.7.0, 3.8.0
            Reporter: Edoardo Comar
         Attachments: edo-connect-mirror-maker-sourcetarget.properties

We observed an excessively delayed emission of the MM2 Checkpoint record.
It only gets created when the source consumer reaches the end of a topic. This 
does not seem reasonable.

In a very simple setup :

Tested with a standalone single process MirrorMaker2 mirroring between two 
single-node kafka clusters(mirromaker config attached) with quick refresh 
intervals (eg 5 sec) and a small offset.lag.max (eg 10)

create a single topic in the source cluster
produce data to it (e.g. 10000 records)
start a slow consumer - e.g. fetching 50records/poll and pausing 1 sec between 
polls which commits after each poll

watch the Checkpoint topic in the target cluster

bin/kafka-console-consumer.sh --bootstrap-server localhost:9192 \
  --topic source.checkpoints.internal \
  --formatter org.apache.kafka.connect.mirror.formatters.CheckpointFormatter \
   --from-beginning

-> no record appears in the checkpoint topic until the consumer reaches the end 
of the topic (ie its consumer group lag gets down to 0).







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