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Status
Current state: Draft
Discussion thread: here
JIRA: KAFKA-3853
Released: <Kafka Version>
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
Motivation
KAFKA-3853 asks for an improvement to the new-consumer
option of the consumer group command. This command, when passed a consumer group that has no consumer (i.e., when the group state is Empty
), currently reports an error indicating that there is no active member:
$ bin/kafka-consumer-groups.sh --new-consumer --bootstrap-server localhost:9092 --describe --group group1 Note: This will only show information about consumers that use the Java consumer API (non-ZooKeeper-based consumers). Error: Consumer group 'group1' has no active members.
The requested improvement is returning offsets within the group (and leaving the owner column empty) instead of returning the error message above. The error message can still be printed to to stderr
as a warning.
When the group is Stable
(i.e. when there are active consumers in the group), the offsets associated with the group are returned as part of the info returned for each consumer in the group in terms of a ConsumerSummary
record. But there is no ConsumerSummary
record if there is no consumer in the group, and therefore, in that scenario a different method is required for extracting those offsets.
Public Interfaces
Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.
A public interface is any change to the following:
Binary log format
The network protocol and api behavior
Any class in the public packages under clientsConfiguration, especially client configuration
org/apache/kafka/common/serialization
org/apache/kafka/common
org/apache/kafka/common/errors
org/apache/kafka/clients/producer
org/apache/kafka/clients/consumer (eventually, once stable)
Monitoring
Command line tools and arguments
- Anything else that will likely break existing users in some way when they upgrade
Proposed Changes
Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.
Compatibility, Deprecation, and Migration Plan
- What impact (if any) will there be on existing users?
- If we are changing behavior how will we phase out the older behavior?
- If we need special migration tools, describe them here.
- When will we remove the existing behavior?
Test Plan
Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?
Rejected Alternatives
If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.