Sean Quah created KAFKA-19424:
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Summary: FindCoordinator inconsistent across brokers when
__consumer_offsets partition count is increased
Key: KAFKA-19424
URL: https://issues.apache.org/jira/browse/KAFKA-19424
Project: Kafka
Issue Type: Bug
Components: group-coordinator
Reporter: Sean Quah
{{GroupCoordinatorService}} captures the number of partitions of
{{__consumer_offsets}} at startup. This is used to map group ids to
{{__consumer_offsets}} partitions in {{GroupCoordinatorService.partitionFor}}.
When adding partitions to {{__consumer_offsets}}, {{GroupCoordinatorService}}
doesn't update its cached partition count. This means that newly started
brokers will map group ids to partitions differently to existing brokers and
FindCoordinator requests can return different results depending on which broker
the client asks.
It's proposed to make brokers consistent by updating the cached partition count
in {{GroupMetadataService.onNewMetadataImage}}.
We should additionally log a warning when the partition count changes, since
adding partitions to {{__consumer_offsets}} is not truly supported, as any
existing group info will remain on the old partition and become un-findable.
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