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Status

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

Discussion thread: here

JIRA: here

Vote thread: Re: [VOTE} KIP-733: change Kafka Streams default replication factor config (there is no DISCUSS thread)

JIRA:

Released: 3.0.0Released: <Kafka Version>

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

Since Kafka 2.4.0, it is possible to rely on the broker default replication factor setting when creating a topic (cf KIP-464: Defaults for AdminClient#createTopic). Even if approved via KIP-464 already, Kafka Streams did not adapt this new feature yet, due to backward compatibility concerns. Given the upcoming major release, we want to enable this feature in Kafka Streams by default now. The main motivation is, that the current default replication.factor=1  puts some burden on users to change the config when they put an application into production. While user are already able to change the config to -1  if their brokers are on 2.4.0 or newer version, it's still an additional config they need to take care of.

Public Interfaces

The default config of replication.factor should be changes.

Proposed Changes

We propose the change the default value of StreamsConfig.REPLICATION_FACTOR_CONFIG from 1 to -1 (meaning use broker default). We also change the "importance level" of replication.factor from HIGH to MEDIUM.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

This change may impact users running Kafka Streams applications against older brokers, i.e., 2.3 or older that don't support the -1 config. For those uses, they would need to change the default before they can start a (new) application.

Note: if an existing application is upgrade, users won't be affected, because if internal replication/changleog topics exist already, no create topic request would be sent anyway. Only if a new application is deployed, or if an existing application is reset, and thus repartition/changelog topics would need to be created users might be affected. Because the application won't startup for this case, the impact is minor and can be considered non-critical. Applications already running in production won't break.

It is unclear how many users might be affected because they use older brokers than 2.4.0. However, we consider it an important improvement for default configs and want to take to opportunity of a major release to make this change (as it's technically breaking backward compatibility).

Test Plan

Regular unit testing is sufficient to ensure that users get a descriptive error message if they hit this client/server incompatibility.

Rejected Alternatives

N/AIf 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.