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Status

Current state:   ["Under Discussion"]

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: here [Change the link from KAFKA-1 to your own ticket]

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

Motivation

Describe the problems you are trying to solve.

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

The documentation says that ReplicationBytes(Out|In)PerSec metrics report "byte out/in (to the other brokers) rate per topic". However, according to the code, it looks like this statement is misleading , and these metrics actually report only per broker metrics. This mismatch between the documentation and actual implementation might cause problems for users who rely on these metrics. For example, as can be seen here Cruise Control relies on these metrics to build a per-topic workload model. (although, it looks like CC authors are aware of the fact that ReplicationBytes(Out|In)PerSec do not report per topic metrics yet). 

Thus, I'm proposing to align the implementation with documentation and make ReplicationBytes(Out|In)PerSec report per topic metrics.

Alternatively, we could align documentation with the implementation and say that ReplicationBytes(Out|In)PerSec report only per broker metrics. I've actually already opened a PR for that. (I'll close the PR if this KIP is accepted)

Public Interfaces

MBean will change from current "kafka.server:type=BrokerTopicMetrics,name=ReplicationBytesInPerSec" to the "kafka.server:type=BrokerTopicMetrics,name=ReplicationBytesInPerSec,topic=([-.\w]+)".  (same for ReplicationBytesOutPerSec)

Proposed Changes

Extend the current implementation of ReplicationBytes(Out|In)PerSec to include per-topic metricsDescribe 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

Since the proposed changes won't remove any existing metrics there shouldn't be any compatibility issues.

Test Plan

Newly added metrics can be tested using a JMX tool, also I think it's possible to implement integration tests.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.