...

This page is meant as a template for writing a KIP. To create a KIP choose Tools->Copy on this page and modify with your content and replace the heading with the next KIP number and a description of your issue. Replace anything in italics with your own description.

Status

Current state:  [One of "Under Discussion", " Accepted", "Rejected"]

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 solveIt's pretty common to have several listeners defined on Kafka brokers. Each listener has its own pool of network threads. In many cases some listeners handle a lot less traffic than others and typically don't need the same number of threads. This KIP proposes optionally setting the sizes of these pool individually using per listener configurations. This will allow fine tuning the number of threads to dynamically accommodate traffic spikes or slightly reduce memory usage when using listeners with different usages.

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 existing configuration "num.network.threads" will be updated to also support being set on specific listener via the "listener.name.<NAME>" notation. Like this other per-listener configuration, the listener name must be provided in lower case.

For example, a valid configuration could be:

listeners=EXTERNAL://:9092,INTERNAL://:9093,CONTROLLER://:9094
advertised.listeners=EXTERNAL://localhost:9092,INTERNAL://localhost:9093,CONTROLLER://localhost:9094
listener.security.protocol.map=EXTERNAL:PLAINTEXT,INTERNAL:PLAINTEXT,CONTROLLER:PLAINTEXT
num.network.threads=16
listener.name.internal.num.network.threads=2

With this configuration, we would end up with:

• 16 threads in the External listener network thread pool
• 2 threads in the Internal listener network thread pool

The control plane listener is not touched by this proposal, it always has a single thread.

Like with the existing configuration, "num.network.threads" per listener configurations will also be reconfigurable. For example, a user could run the following command to have 3 threads in the Internal listener network thread pool.

./bin/kafka-configs.sh --bootstrap-server localhost:9092 --entity-type brokers --entity-default --alter --add-config listener.name.internal.num.network.threads=3

The documentation will be adjusted to mention it can optionally be configured on a specific listener:
Listener-level limits may also be configured by prefixing the config name with the listener prefix, for example, listener.name.internal.num.network.threads

Proposed Changes

Most of the changes are in SocketServer where the logic creating Acceptors and Processors lives. To make this reconfigurable, the data plane acceptor will have to implement ListenerReconfigurable. Also the logic to create Processors will be moved directly inside Acceptor instead of being driven by SocketServerDescribe 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?

Rejected Alternatives

This is a new configuration option. This changes nothing for existing Kafka environments.

Rejected Alternatives

NoneIf 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.