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Authors Mehari Beyene, Divij Vaidya

Status

Current state:"Under Discussion"

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

JIRA: KAFKA-7739

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

Motivation

This proposal aims to address a gap in the existing functionality introduced by KIP 405, which enabled customers to enable Tiered Storage but did not provide the capability to disable it. To enhance the flexibility and control of data storage in Kafka clusters, we propose the introduction of a Tiered Storage disablement feature. This feature will allow customers to selectively disable Tiered Storage on a per-topic basis. There are several reasons why customers would be interested in this feature:

1. Flexibility: Currently, customers can enable Tiered Storage but lack the ability to disable it, creating a one-way decision that may discourage them from fully exploring the feature. By introducing the Tiered Storage disablement feature, we offer customers the flexibility to enable or disable the feature as needed, empowering them to make informed choices that align with their specific requirements.
2. Cost Optimization: When data is duplicated in both local and tiered storage, it incurs costs for both tiers. However, not all customers require long-term tiered storage for their data. By providing the option to disable the feature, customers can save costs when Tiered Storage is not necessary, allowing them to optimize their expenses without compromising data retention needs.
3. Temporary or Experimental Setups: The Tiered Storage disablement feature grants customers the ability to conduct temporary experiments and evaluate the benefits of tiered storage without committing to a permanent architectural change in their data pipelines. By enabling customers to disable Tiered Storage when not needed, they can easily evaluate the impact and advantages of the feature, fostering a culture of experimentation and informed decision-making.
4. Compatibility: Allowing customers to disable the Tiered Storage feature enhances the compatibility of Kafka clusters. It enables seamless migration between different Kafka versions or service providers that may not support Tiered Storage. By offering the option to disable Tiered Storage, customers can smoothly transition their Kafka deployments, ensuring compatibility and reducing potential operational challenges.

Goals/Requirements

1. Disable Tiering on a Topic: Customers should have the ability to disable tiering on a topic that has Tiered Storage enabled.
2. Retention of Tiered Data: When disabling tiered storage on a topic, customers should have the option to retain the tiered data according to the configured retention policy prior to disabling tiering.
3. Deletion of Tiered Data: When disabling tiered storage on a topic, customers should have the option to delete the tiered data in the remote storage associated with that topic.
4. Fetching Previously Tiered Data: Customers should have the option to continue fetching data that was previously tiered before the tiered storage disablement. This allows them to access and consume the tiered data even after the tiering feature has been disabled.
5. Re-enabling Tiering on a Previously Disabled Topic: Customers should be able to re-enable tiering on a topic that was previously disabled, allowing them to resume tiered storage for that specific topic.
6. Support for Both Kraft and ZooKeeper-Based Clusters: The tiered storage disablement feature should be designed and implemented to support both Kraft and ZooKeeper-based Kafka clusters, ensuring compatibility across different cluster configurations.

Non-Goals

The following aspects are considered as non-goals for the tiered storage disablement feature:

1. System-Wide Disablement: The tiered storage disablement feature does not aim to support the system-wide disablement of tiered storage on a cluster level, as this is controlled by the cluster-level configuration remote.log.storage.system.enable.
2. Support for Compacted Topics: Tiered Storage is not supported for compacted topics, and this behavior will remain unchanged. During re-enablement, the feature will not support tiered storage for compacted topics. When initially enabling tiered storage for a topic, we check that the topic does not have compaction enabled, however, if the topic has historically used a compaction policy, we do not perform deep check to restrict tiered storage enablement. This behavior will remain consistent during re-enablement as well.

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.