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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 object can be created for the usage in console consumer and via the DSL. 

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Proposed Changes

Here are the changes being proposed in the KIP:

1. StreamsConfig
   1. Deprecate default.windowed.key.serde.inner

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1. 1.  and default.windowed.

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1. 1. value.serde.inner

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1. 1. . 
   2. Introduce a new config called windowed.deserializer.inner.class

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1. 1. . 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

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Proposed Changes

Here are the changes being proposed in the KIP:

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1. 1. will use Deserialiser class here directly instead of a Serde.

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1. 1. 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

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1. 1. windowed.deserializer.inner.class 

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1. 1. and window.size.ms config. 
2. TimeWindowedDeserializer

1. 1. 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. 
   2. 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.
   3. 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.
2. 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:
  • Rename Deprecate default.windowed.key.serde.innerto  and default.windowed.deserializervalue.serde.inner in StreamConfig.class. 
  • Deprecate Introduce a new config called default.windowed.valuedeserializer.serdeinner.innerclass. 
    

    
    

    Code Block
    language java theme Midnight
    public static final String WINDOWED_DESERIALISER_INNER_CLASS = "windowed.deserializer.inner.class"; private static final String WINDOWED_DESERIALISER_INNER_CLASS_DOC = " Deserializer for the inner class of a windowed keyrecord. Must implement the " + "<code>org.apache.kafka.common.serialization.Deserializer</code> interface. Note that setting this config in KafkaStreams application would result " + "in and error as it is meant to be used only from Plain consumer client."; @Deprecated public static final String DEFAULT_WINDOWED_VALUEKEY_SERDE_INNER_CLASS = "default.windowed.valuekey.serde.inner";

• ConsoleConsumer
  • It would be mandatory to pass windowed.deserializer.inner.class and window.size.ms config. <Need to check how to do this>
• TimeWindowedDeserializer
  • Inside configure method, ensure that innerClassDeserialiser passed via constructor and the config are not conflicting. What it means is that:
  • If both inner and windowedDeserialiserInnerClass are set, then they should be the pointing to the same class.
  • Atleast one of inner and windowedDeserialiserInnerClass are set.
  Code Block

  language	java
  theme	Midnight

  if (innerClassDeserializer != null && configInnerClassDeserializer != null) { if (innerClassDeserializer != configInnerClassDeserializer) throw new IllegalArgumentException("Inner class deserializer passed via constructor and config windowed.deserializer.inner.class should match"); } else if (innerClassDeserializer == null && configInnerClassDeserializer == null) { throw new IllegalArgumentException("Inner class deserializer should be passed either via constructor or via "); }

  @Deprecated public static final String DEFAULT_WINDOWED_VALUE_SERDE_INNER_CLASS = "default.windowed.value.serde.inner";

  
  

Compatibility, Deprecation, and Migration Plan

Since This KIP deprecates following 2 configs in StreamConfig : default.windowed.key.serde.innerconfig is being rename to windowed.deserializer.inner.class in StreamConfig and also  and default.windowed.value.serde.inner is being deprecated, we will have to follow a deprecation path for the same. We can maybe enforce the removal of the deprecated configs and then enforce users?inner

Rejected Alternatives

N/A