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Status

Current state:  Under DiscussionAdopted

Discussion thread: [DISCUSS] KIP-446: Add changelog topic configuration to KTable suppresshere [Change the link from the KIP proposal email archive to your own email thread]

JIRA:

Implemented: 2.6.0

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

Motivation

When suppressing record updates in a KTable, an internal changelog topic is created.Currently the streams DSL does not provide a way to configure this topic. The suppress operator sends a record to the topic when it is received from upstream, and sends a tombstone after it is emtited.  Thus, data in the buffer is much shorter lived than data in other KTables, and the buffer changelog also may be much more compactable than KTable changelogs. Currently the configuration for this topic cannot be set using the Streams DSL, instead a user has to run an external tool to override the defaults.

Other parts of the Streams API that create internal topics do allow for a user to set their configuration. When aggregating a stream, for example, an instance of Materialized is passed to the aggregate method which holds a topicConfig of type Map<String, String>.

Public Interfaces

Add `withLoggingEnabled/Disabled` to BufferConfig

We add two methods  to {code}BufferConfig{code}

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

...

Suppressed.BufferConfig.

• withLogginEnabled: (default) enables logging and allows for configuration of the changelog topic
• withLoggingDisabled: disables logging to the changelog topic

When none of the above methods is called, the behavior will be no different from the current implementation, i.e., records will be written to a changelog topic with the default settings.

Public Interfaces

The public interface of BufferConfig will change to include the previously mentioned methods.

public interface Suppressed<K> {

    interface BufferConfig<BC extends BufferConfig<BC>> {
        /**
         * Disable the changelog for store built by this {@link StoreBuilder}.
         * This will turn off fault-tolerance for your store.
         * By default the changelog is enabled.
         * @return this
         */
        BC withLoggingDisabled();

        /**
         * Indicates that a changelog topic should be created containing the currently suppressed 
         * records. Due to the short-lived nature of records in this topic it is likely more
         * compactable than changelog topics for KTables.
         *
         * @param config Configs that should be applied to the changelog. Note: Any unrecognized
         * configs will be ignored.
         * @return this
         */
        BC withLoggingEnabled(final Map<String, String> config);
    }
}

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

The impact on existing applications will be non-existant as this change does not remove or alter existing behavior.

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.