Greg Harris created KAFKA-17232:
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Summary: MirrorCheckpointConnector does not generate task configs
if initial consumer group load times out
Key: KAFKA-17232
URL: https://issues.apache.org/jira/browse/KAFKA-17232
Project: Kafka
Issue Type: Bug
Components: mirrormaker
Affects Versions: 3.9.0
Reporter: Greg Harris
The MirrorCheckpointConnector has two operations that read the source consumer
groups:
* loadInitialConsumerGroups
* refreshConsumerGroups
loadInitialConsumerGroups blocks the start() method of the connector, while
refreshConsumerGroups is asynchronous and runs periodically while the connector
is running.
loadInitialConsumerGroups may take a long time to execute, and may exceed the
configured "admin.timeout.ms" used by the Scheduler. This timeout is logged and
the start() method returns normally. If this happens, the framework will
generate task configs immediately after start(), before
loadInitialConsumerGroups can finish, and will generate an empty set of task
configs:
[https://github.com/apache/kafka/blob/e2494e6ffb89f8288ed2aeb9b5596c755210bffd/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorCheckpointConnector.java#L118-L121].
Later, when loadInitialConsumerGroups completes, it will not request task
reconfiguration, believing it is the initial load operation.
Later still, when refreshConsumerGroups completes, it will not request task
reconfiguration, as the set of consumer groups has not changed since the
initial load:
[https://github.com/apache/kafka/blob/e2494e6ffb89f8288ed2aeb9b5596c755210bffd/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorCheckpointConnector.java#L173-L180]
This leads to a situation where the MirrorCheckpointConnector believes it has
converged with nothing to update, but actually has consumer groups that are not
allocated to tasks.
This happens particularly for large, stable Kafka clusters with many consumer
groups that are not being actively created or deleted.
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