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Status

Current state:  Under DiscussionAccepted

Discussion thread: TODO here 

Voting thread:here

JIRA: TODO KAFKA-20229 

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

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We have the RemoteClusterUtils API to enable users to perform some operations of their MirrorMaker environmentenvironments. One method from this API, translateOffsets(), allows to manually translate consumer group offsets. This is useful when MirrorCheckpointConnector is not configured to automatically sync offsets or when dealing with a disaster and unplanned failover. This method works by fully reading the checkpoints topic which is populated by MirrorCheckpointConnector, so this can be an expensive call and it can take a long time if depending on the size of the topic is large. This method takes a single consumer group id as input, so it makes it unusable unsuitable in cases when the offsets of several consumer groups have to be translated as each call re-reads the full topic. 

Since the full topic is read anyway, we should have a method to translate the committed offsets of multiple consumer groups at the same time.

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

A new translateOffsets() method in RemoteClusterUtils that takes a regex pattern to specify the consumer groups:

/**
 * Translates remote consumer groups' offsets into corresponding local offsets. Topics are automatically
 *  renamed according to the configured {@link ReplicationPolicy}.
 *  @param properties Map of properties to instantiate a {@link MirrorClient}
 *  @param remoteClusterAlias The alias of the remote cluster
 *  @param consumerGroupPattern The regex pattern specifying the consumer groups to translate offsets for
 *  @param timeout The maximum time to block when consuming from the checkpoints topic
 *  @throws IllegalArgumentException If any of the arguments are null
 */
public static Map<String, Map<TopicPartition, OffsetAndMetadata>> translateOffsets(Map<String, Object> properties, String remoteClusterAlias, Pattern consumerGroupPattern, Duration timeout) {
}

The matching method in MirrorClient:

/**
 * Translates remote consumer groups' offsets into corresponding local offsets. Topics are automatically
 * renamed according to the ReplicationPolicy.
 * @param consumerGroupPattern The regex pattern specifying the consumer groups to translate offsets for
 * @param remoteClusterAlias The alias of remote cluster
 * @param timeout The maximum time to block when consuming from the checkpoints topic
 * @throws IllegalArgumentException If any of the arguments are null
 */
public Map<String, Map<TopicPartition, OffsetAndMetadata>> remoteConsumerOffsets(Pattern consumerGroupPattern, String remoteClusterAlias, Duration timeout) {
}

Proposed Changes

The existing MirrorClient.remoteConsumerOffsets() will invoke the new method with a regex just matching the specified consumer group Id.  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

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• This is adding new methods. There are no behavior changes to existing methods.

Test Plan

The new methods will be tested using unit tests. This will require some refactoring in MirrorClient to make the remoteConsumerOffsets() method testable (we currently don't have tests for that method).

Rejected Alternatives

• Deprecate the existing RemoteClusterUtils.translateOffsets() and MirrorClient.remoteConsumerOffsets() methods: Internally these will use the same logic as the new methods, so we can keep them.
• Specify the desired consumer groups via a collection: This limits the ability of translating all consumer group offsets.