Table of Contents

Status

Current state:  "DISCUSS"Adopted

Discussion thread: 

JIRA: KAFKA-12313

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

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 deserializer 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 windowwindowed.inner.class.deserializerserde. 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. Also, as per the proposed changes below, this config is to be used really from the console consumer so we will use Deserialiser class here directly instead of a Serde. Note that setting this config from KafkaStreams application would lead to an error being thrown as this config is to be used only from plain Consumer Client.
2. ConsoleConsumer
   1. It would be mandatory to pass windowwindowed.inner.class.deserializerserde and window.size.ms 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

4. If the users want to run Console consumer for testing purposes, then it will invoke the default constructor of TimeWindowedDeserializer. We will ensure that both the configs (windowSize and deserialiser class) are set and if they aren't then an error would be thrown. 
5. For any other plain consumer client, the user can pass them in as configs OR pass the parameters to the TimeWindowedDeserializer constructor, and then pass that object to the consumer. It is ok for the user to pass both as long as there is no conflict between the params passed via constructor and via the configs.
6. For use in Kafka Streams (such as the DSL), the user must supply the parameters by constructing a TimeWindowedSerde and passing that in as a parameter to any relevant DSL operators. This is already supported so no change is needed here.

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

Similar to the checks added in KIP-659 to validate the windownSize config, a check would be added for deserialiserInnerClass. This would ensure that it has only 1 valid value.

Public Interfaces

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

      
      

      Code Block
      language java theme Midnight
      public static final String

    WINDOW

    • WINDOWED_INNER_CLASS_

    DESERIALISER

    • SERDE = "

    window

    • windowed.inner.class.

    deserializer

    • serde"; private static final String

    WINDOW

    • WINDOWED_INNER_CLASS_

    DESERIALISER

    • SERDE_DOC = "

    Deserializer

    • Serde for the inner class of a windowed record. Must implement the " + "<code>org.apache.kafka.common.serialization.

    Deserializer<

    • Serde</code> interface. Note that setting this config in KafkaStreams application would result " + "in

    and

    • 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