Status

Current state: Adopted

Discussion thread: 

JIRA: KAFKA-12313

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Motivation

KIP-659 introduced a config windowSize to TimeWindowedDeserializer which discourages the setting of windowSize to Long.MAX_VALUE as the default value. However, there is still a possibility of setting the config only for innerClassSerde or only for windowSize. This KIP aims at standardising the way the serialisers and deserializer object can be created for the usage in console consumer, plain consumer and via the DSL. 

Proposed Changes

Here are the changes being proposed in the KIP:

1. StreamsConfig
   1. Deprecate default.windowed.key.serde.inner and default.windowed.value.serde.inner. 
   2. Introduce a new config called windowed.inner.class.serde. This way, the config comes closer to the window.size.ms config introduced in KIP-659 and it also emphasises that the config isn't really a default one.
2. ConsoleConsumer
   1. It would be mandatory to pass windowed.inner.class.serde and window.size.ms config. 
3. The following table discusses the proposed changes for the Windowed Serdes and proposed changes based on Client Type.

   	Windowed Serde Type	Client Type	Constructor Invoked	Proposed Change
   1	TimeWindowedDeserializer	Console Consumer	Default constructor	Ensure both windowSize and Serde class configs are set. Throw error if not.
   		Plain Consumer	Default OR Parameterised	Ok to use either as long as the configs supplied don't conflict.
   		Kafka Streams	Parameterised	User supplies parameters by constructing a TimeWindowedSerde object. No change
   2	TimeWindowedSerializer	Console Producer	Default constructor	Ensure Serde class config is set. Throw error if not.
   		Plain Producer	Default OR Parameterised	Ok to use either as long as the configs supplied don't conflict.
   		Kafka Streams	Parameterised	User supplies parameters by constructing a TimeWindowedSerde object. No change
   3	SessionWindowedDeserializer	Console consumer	Default constructor	Ensure Serde class config is set. Throw error if not.
   		Plain consumer	Default OR Parameterised	Ok to use either as long as the configs supplied don't conflict.
   		Kafka Streams	Parameterised	User supplies parameters by constructing a SessionWindowedSerde object. No change
   4	SessionWindowedSerializer	Console Producer	Default constructor	Ensure Serde class config is set. Throw error if not.
   		Plain Producer	Default OR Parameterised	Ok to use either as long as the configs supplied don't conflict.
   		Kafka Streams	Parameterised	User supplies parameters by constructing a SessionWindowedSerde object. No change

Public Interfaces

• StreamsConfig:
  • Deprecate default.windowed.key.serde.inner and default.windowed.value.serde.inner in StreamConfig. 
    • Introduce a new config called windowed.inner.class.serde. 
      

          public static final String WINDOWED_INNER_CLASS_SERDE = "windowed.inner.class.serde";
          private static final String WINDOWED_INNER_CLASS_SERDE_DOC = " Serde for the inner class of a windowed record. Must implement the " +
              "<code>org.apache.kafka.common.serialization.Serde</code> interface. Note that setting this config in KafkaStreams application would result " + 
      		"in an error as it is meant to be used only from Plain consumer client.";
      
      	@Deprecated
      	public static final String DEFAULT_WINDOWED_KEY_SERDE_INNER_CLASS = "default.windowed.key.serde.inner";
      
      	@Deprecated
      	public static final String DEFAULT_WINDOWED_VALUE_SERDE_INNER_CLASS = "default.windowed.value.serde.inner";

Compatibility, Deprecation, and Migration Plan

This KIP deprecates following 2 configs in StreamConfig : default.windowed.key.serde.inner and default.windowed.value.serde.inner

Rejected Alternatives

N/A