Table of Contents

Status

Current state: "under discussionaccepted"

Discussion thread: HERE HERE

JIRA: K AFKA-4218, KAFKA-4726 , KAFKA-3745, KAFKA-7842, KAFKA-7843

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

The PR can be found here.

Motivation

(taken from JIRA descriptions)

Key access to ValueTransformer: While transforming values via KStream.transformValues and ValueTransformer, the key associated with the value may be needed, even if it is not changed. For instance, it may be used to access stores.
As of now, the key is not available within these methods and interfaces, leading to the use of KStream.transform and Transformer, and the unnecessary creation of new KeyValue objects.
Key access to ValueMapper: ValueMapper should have read-only access to the key for the value it is mapping. Sometimes the value transformation will depend on the key.
It is possible to do this with a full blown KeyValueMapper but that loses the promise that you won't change the key – so you might introduce a re-keying phase that is totally unnecessary.
Key access to ValueJoiner interface: In working with Kafka Stream joining, it's sometimes the case that a join key is not actually present in the values of the joins themselves (if, for example, a previous transform generated an ephemeral join key.) In such cases, the actual key of the join is not available in the ValueJoiner implementation to be used to construct the final joined value. This can be worked around by explicitly threading the join key into the value if needed, but it seems like extending the interface to pass the join key along as well would be helpful

Additionally we consider adding key access to Initializer and Reducer interfaces.

Public Changes

There are no public changes to ensure the backwards-compatibility.

Proposed Changes

KStream interface:

Code Block

language	java

<GK, GV, RV> KStream<K, RV> leftJoin(final GlobalKTable<GK, GV> globalKTable,

We extend the target interfaces ValueJoiner, ValueTransformer, and

ValueMapper as ValueJoinerWithKey,  ValueTransformerWithKey, and ValueMapperWithKey. In extended abstract classes we have an access to keys.

In Processor we check the actual instance of object:

this.valueTransformer = valueTransformer;
if (valueTransformer instanceof ValueTransformerWithKey) {
    isTransformerWithKey = true;
} else {
    isTransformerWithKey = false;
}

..............

@Override
public void process(K key, V value) {
if (isTransformerWithKey) {

K

final

keyCopy

KeyValueMapper<?

=

super

(

) Utils.deepCopy(key);
context.forward(key, ((ValueTransformerWithKey<K, V, R>) valueTransformer).transform(keyCopy, value));
} else {

, ? super V, ? extends GK> keyValueMapper,

context.forward(key,

valueTransformer.transform(value));
}
}

As we can see from the above code snippet, we can guard the key change in Processors by deeply copying the object before calling the apply() method.

The PR can be found here.

Test Plan

The unit tests are changed accordingly to support the changes in core classes.

Rejected Alternatives

Not backward-compatible

We propose adding key information for ValueJoiner, ValueTransformer, and ValueMapper classes and their apply(...) methods.

As a result, we perform the following public changes (and their overloaded versions)

                 final ValueJoinerWithKey<? super K, ? super V, ? super GV, ? extends RV> valueJoinerWithKey);

<GK, GV, RV> KStream<K, RV> join(final GlobalKTable<GK, GV> globalKTable,
                                 final KeyValueMapper<? super K, ? super V, ? extends GK> keyValueMapper,
                                 final ValueJoinerWithKey<? super K, ? super V, ? super GV, ? extends RV> valueJoinerWithKey);
 
<VT, VR> KStream<K, VR> leftJoin(final KTable<K, VT> table,
                                 final ValueJoinerWithKey<? super K, ? super V, ? super VT, ? extends VR> valueJoinerWithKey,
                                 final Serde<K> keySerde,
                                 final Serde<V> valSerde);

<VT, VR> KStream<K, VR> leftJoin(final KTable<K, VT> table,
                                 final ValueJoinerWithKey<? super K, ? super V, ? super VT, ? extends VR> valueJoinerWithKey);

<VT, VR> KStream<K, VR> join(final KTable<K, VT> table,
                             final ValueJoinerWithKey<? super K, ? super V, ? super VT, ? extends VR> valueJoinerWithKey,
                             final Serde<K> keySerde,
                             final Serde<V> valSerde);

<VT, VR> KStream<K, VR> join(final KTable<K, VT> table,
                             final ValueJoinerWithKey<? super K, ? super V, ? super VT, ? extends VR> valueJoinerWithKey);

<VO, VR> KStream<K, VR> outerJoin(final KStream<K, VO> otherStream,
                                  final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> valueJoinerWithKey,
                                  final JoinWindows windows,
                                  final Serde<K> keySerde,
                                  final Serde<V> thisValueSerde,
                                  final Serde<VO> otherValueSerde);

<VO, VR> KStream<K, VR> outerJoin(final KStream<K, VO> otherStream,
                                  final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> valueJoinerWithKey,
                                  final JoinWindows windows);

 
<VO, VR> KStream<K, VR> leftJoin(final KStream<K, VO> otherStream,
                                 final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> valueJoinerWithKey,
                                 final JoinWindows windows,
                                 final Serde<K> keySerde,
                                 final Serde<V> thisValSerde,
                                 final Serde<VO> otherValueSerde);

<VO, VR> KStream<K, VR> leftJoin(final KStream<K, VO> otherStream,
                                 final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> valueJoinerWithKey,
                                 final JoinWindows windows);

<VO, VR> KStream<K, VR> join(final KStream<K, VO> otherStream,
                             final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> valueJoinerWithKey,
                             final JoinWindows windows,
                             final Serde<K> keySerde,
                             final Serde<V> thisValueSerde,
                             final Serde<VO> otherValueSerde);

<VO, VR> KStream<K, VR> join(final KStream<K, VO> otherStream,
                             final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> valueJoinerWithKey,
                             final JoinWindows windows);

<VR> KStream<K, VR> transformValues(final ValueTransformerWithKeySupplier<? super K, ? super V, ? extends VR> valueTransformerWithKeySupplier,
                                    final String... stateStoreNames);

<VR> KStream<K, VR> mapValues(ValueMapperWithKey<? super K, ? super V, ? extends VR> mapperWithKey);

KTable interface:

Code Block

language	java
title	KTable interface

<VO, VR> KTable<K, VR> join(final KTable<K, VO> other,
                            final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> joiner);

<VO, VR> KTable<K, VR> join(final KTable<K, VO> other,
                            final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> joiner,
                            final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized);                                

<VO, VR> KTable<K, VR> join(final KTable<K, VO> other,
                            final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> joiner,
                            final Named named);

<VO, VR> KTable<K, VR> join(final KTable<K, VO> other,
                            final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> joiner,
                            final Named named,
                            final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized);

<VR, KO, VO> KTable<K, VR> join(final KTable<KO, VO> other,
                                final Function<V, KO> foreignKeyExtractor,
                                final ValueJoinerWithKey<KO, V, VO, VR> joiner);                                

<VR, KO, VO> KTable<K, VR> join(final KTable<KO, VO> other,
                                final Function<V, KO> foreignKeyExtractor,
                                final ValueJoinerWithKey<KO, V, VO, VR> joiner,
                                final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized);

<VR, KO, VO> KTable<K, VR> join(final KTable<KO, VO> other,
                                final Function<V, KO> foreignKeyExtractor,
                                final ValueJoinerWithKey<KO, V, VO, VR> joiner,
                                final Named named);

<VR, KO, VO> KTable<K, VR> join(final KTable<KO, VO> other,
                                final Function<V, KO> foreignKeyExtractor,
                                final ValueJoinerWithKey<KO, V, VO, VR> joiner,
                                final Named named,
                                final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized);


<VO, VR> KTable<K, VR> leftJoin(final KTable<K, VO> other,
                                final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> joiner);

<VO, VR> KTable<K, VR> leftJoin(final KTable<K, VO> other,
                                final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> joiner,
                                final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized);                                

<VO, VR> KTable<K, VR> leftJoin(final KTable<K, VO> other,
                                final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> joiner,
                                final Named named);

<VO, VR> KTable<K, VR> leftJoin(final KTable<K, VO> other,
                                final ValueJoinerWithKey<? super K, ? super V, ? super VO, ? extends VR> joiner,
                                final Named named,
                                final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized);

<VR, KO, VO> KTable<K, VR> leftJoin(final KTable<KO, VO> other,
                                    final Function<V, KO> foreignKeyExtractor,
                                    final ValueJoinerWithKey<KO, V, VO, VR> joiner);                                

<VR, KO, VO> KTable<K, VR> leftJoin(final KTable<KO, VO> other,
		                            final Function<V, KO> foreignKeyExtractor,
		                            final ValueJoinerWithKey<KO, V, VO, VR> joiner,
		                            final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized);

<VR, KO, VO> KTable<K, VR> leftJoin(final KTable<KO, VO> other,
	                                final Function<V, KO> foreignKeyExtractor,
	                                final ValueJoinerWithKey<KO, V, VO, VR> joiner,
	                                final Named named);

<VR, KO, VO> KTable<K, VR> join(final KTable<KO, VO> other,
                                final Function<V, KO> foreignKeyExtractor,
                                final ValueJoinerWithKey<KO, V, VO, VR> joiner,
                                final Named named,
                                final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized);

- KGroupedStream interface:

Code Block

language	java

KTable<K, V> reduce(final ReducerWithKey<K, V> reducerWithKey);
 
KTable<K, V> reduce(final ReducerWithKey<K, V> reducerWithKey,
                    final String queryableStoreName);
 
KTable<K, V> reduce(final ReducerWithKey<K, V> reducerWithKey,
                    final StateStoreSupplier<KeyValueStore> storeSupplier);
 
<W extends Window> KTable<Windowed<K>, V> reduce(final ReducerWithKey<K, V> reducerWithKey,
                                                 final Windows<W> windows,
                                                 final String queryableStoreName);
<W extends Window> KTable<Windowed<K>, V> reduce(final Reducer<V> reducer,
                                                 final Windows<W> windows);
 
<W extends Window> KTable<Windowed<K>, V> reduce(final ReducerWithKey<K, V> reducerWithKey,
                                                 final Windows<W> windows,
                                                 final StateStoreSupplier<WindowStore> storeSupplier);
 
KTable<Windowed<K>, V> reduce(final ReducerWithKey<K, V> reducerWithKey,
                              final SessionWindows sessionWindows,
                              final String queryableStoreName);
 
KTable<Windowed<K>, V> reduce(final ReducerWithKey<K, V> reducerWithKey,
                              final SessionWindows sessionWindows);
 
KTable<Windowed<K>, V> reduce(final ReducerWithKey<K, V> reducerWithKey,
                              final SessionWindows sessionWindows,
                              final StateStoreSupplier<SessionStore> storeSupplier);
 
 
 
 
<VR> KTable<K, VR> aggregate(final InitializerWithKey<K, VR> initializerWithKey,
                             final Aggregator<? super K, ? super V, VR> aggregator,
                             final Serde<VR> aggValueSerde,
                             final String queryableStoreName);
 
<VR> KTable<K, VR> aggregate(final InitializerWithKey<K, VR> initializerWithKey,
                             final Aggregator<? super K, ? super V, VR> aggregator,
                             final Serde<VR> aggValueSerde);
 
<VR> KTable<K, VR> aggregate(final InitializerWithKey<K, VR> initializerWithKey,
                             final Aggregator<? super K, ? super V, VR> aggregator,
                             final StateStoreSupplier<KeyValueStore> storeSupplier);
 
<W extends Window, VR> KTable<Windowed<K>, VR> aggregate(final InitializerWithKey<K, VR> initializerWithKey,
                                                         final Aggregator<? super K, ? super V, VR> aggregator,
                                                         final Windows<W> windows,
                                                         final Serde<VR> aggValueSerde,
                                                         final String queryableStoreName);
 
<W extends Window, VR> KTable<Windowed<K>, VR> aggregate(final InitializerWithKey<K, VR> initializerWithKey,
                                                         final Aggregator<? super K, ? super V, VR> aggregator,
                                                         final Windows<W> windows,
                                                         final Serde<VR> aggValueSerde);
 
<W extends Window, VR> KTable<Windowed<K>, VR> aggregate(final InitializerWithKey<K, VR> initializerWithKey,
                                                         final Aggregator<? super K, ? super V, VR> aggregator,
                                                         final Windows<W> windows,
                                                         final StateStoreSupplier<WindowStore> storeSupplier);
 
 
 
<T> KTable<Windowed<K>, T> aggregate(final InitializerWithKey<K, VR> initializerWithKey,
                                     final Aggregator<? super K, ? super V, T> aggregator,
                                     final Merger<? super K, T> sessionMerger,
                                     final SessionWindows sessionWindows,
                                     final Serde<T> aggValueSerde,
                                     final String queryableStoreName);
 
 
<T> KTable<Windowed<K>, T> aggregate(final InitializerWithKey<K, VR> initializerWithKey,
                                     final Aggregator<? super K, ? super V, T> aggregator,
                                     final Merger<? super K, T> sessionMerger,
                                     final SessionWindows sessionWindows,
                                     final Serde<T> aggValueSerde);
 
 
<T> KTable<Windowed<K>, T> aggregate(final Initializer<T> initializer,
                                     final Aggregator<? super K, ? super V, T> aggregator,
                                     final Merger<? super K, T> sessionMerger,
                                     final SessionWindows sessionWindows,
                                     final Serde<T> aggValueSerde,
                                     final StateStoreSupplier<SessionStore> storeSupplier);

Proposed Changes

Handling lambdas

For ValueMapper, ValueJoiner and their "withKey" interfaces we support lambdas. For ValueTransformer interface we don't need lambdas by the core definition of the class.

To support lambdas, we separate withKey interface from original ones, meaning we don't inherit or extend from one to another.

ValueMapperWithKey

Code Block

language	java

public interface ValueMapperWithKey<K, V, VR> {
    VR apply(final K readOnlyKey, final V value);
}

ValueJoinerWithKey

Code Block

language	java

public interface ValueJoinerWithKey<K, V1, V2, VR> {
    VR apply(final K readOnlyKey, final V1 value1, final V2 value2);
}

ValueTransformerWithKeySupplier

Code Block

language	java

public interface ValueTransformerWithKeySupplier<K, V, VR> {
    ValueTransformerWithKey<K, V, VR> get();
}
 
public interface ValueTransformerWithKey<K, V, VR> {
	void init(final ProcessorContext context);
    VR transform(final K readOnlyKey, final V value);
    void close();
}

ReducerWithKey

Code Block

language	java

public interface ReducerWithKey<K, V> {
	V apply(final K readOnlyKey, final V value1, final V value2);
}

InitializerWithKey

Code Block

language	java

public interface InitializerWithKey<K, VA> {
	VA apply(final K readOnlyKey);
}

Handling withKey interfaces while building the topology

In general, we change the constructors of all related backend Processors to be withKey types as we can easily convert regular (withoutKey) interfaces to withKey interfaces.

```
ValueMapperWithKey
```

Code Block

language	java

@Override
public <V1> KStream<K, V1> mapValues(final ValueMapper< ? super V, ? extends V1> mapper) {
    Objects.requireNonNull(mapperWithKey, "mapperWithKey can't be null");
    String name = topology.newName(MAPVALUES_NAME);
    final ValueMapperWithKey<K, V, V1> valueMapperWithKey = new ValueMapperWithKey<K, V, V1>() {
            @Override
            public V1 apply(K key, V value) {
                return mapper(value);
            }
        };
    }
    topology.addProcessor(name, new KStreamMapValues<>(valueMapperWithKey), this.name);
    return new KStreamImpl<>(topology, name, sourceNodes, this.repartitionRequired);
}

```
ValueJoinerWithKey
```

Code Block

language	java

static <K, T1, T2, R> ValueJoinerWithKey<K, T1, T2, R> convertToValueJoinerWithKey(final ValueJoiner<T1, T2, R> valueJoiner) {
    Objects.requireNonNull(valueJoiner, "valueJoiner can't be null");
    return new ValueJoinerWithKey<K, T1, T2, R>() {
        @Override
        public R apply(K key, T1 value1, T2 value2) {
            return valueJoiner.apply(value1, value2);
        }
    };
}


public <V1, R> KStream<K, R> leftJoin(
    final KStream<K, V1> other,
    final ValueJoiner<? super V, ? super V1, ? extends R> joiner,
    final JoinWindows windows,
    final Serde<K> keySerde,
    final Serde<V> thisValSerde,
    final Serde<V1> otherValueSerde) {

    return doJoin(other,
        convertToValueJoinerWithKey(joiner),   // doJoin, join methods, and corresponding Processors accept ValueJoinerWithKey type.
        windows,
        keySerde,
        thisValSerde,
        otherValueSerde,
        new KStreamImplJoin(true, false));
}

Test Plan

The unit tests are changed accordingly to support the changes in core classes.

Rejected Alternatives

Lambdas are not supported

This document is proposed with ValueMapper example but it can be applied to other interfaces as well. Rich functions are proposed:

public interface RichFunction {
    void init(final ProcessorContext context);

 void close();
}

public abstract class AbstractRichFunction implements RichFunction {
    @Override
  public void init(final ProcessorContext context) {}

    @Override
  public void close() {}
}

public abstract class RichValueJoiner<K, V1, V2, VR> extends AbstractRichFunction implements ValueJoiner<V1, V2, VR>  {
    @Override
  public final VR apply(final V1 value1, final V2 value2) {
        return apply(null, value1, value2);
  }

    public abstract VR apply(final K key, final V1 value1, final V2 value2);
}

Inside processor, we check if the instance (for example ValueMapper instance) is rich (for example RichValueMapper):

KStreamFlatMapValues(ValueMapper<? super V, ? extends Iterable<? extends V1>> mapper) {
    this.mapper = mapper;
  isRichFunction = mapper instanceof RichValueMapper ? true : false;
}

@Override
public void process(K key, V value) {
    Iterable<? extends V1> newValues;
 if (isRichFunction) {
        newValues = ((RichValueMapper<? super K, ? super V, ? extends Iterable<? extends V1>>) mapper).apply(key, value);
  } else {
        newValues = mapper.apply(value);
  }
    for (V1 v : newValues) {
        context().forward(key, v);
  }
}

Not backward-compatible

We propose adding key information for ValueJoiner, ValueTransformer, and ValueMapper classes and their apply(...) methods.

As a result, we perform the following public changes (and their overloaded versions)

ClassOldNewKStream<VR> KStream<K, VR> mapValues(

Class	Old	New
KStream	<VR> KStream<K, VR> mapValues(ValueMapper<? super V, ? extends VR> mapper);	<VR> KStream<K, VR> mapValues(ValueMapper<? super K, ? super V, ? extends VR> mapper);
KStream	<VR> KStream<K, VR> transformValues(final ValueTransformerSupplier<? super V, ? extends VR> valueTransformerSupplier, final String... stateStoreNames);	<VR> KStream<K, VR> transformValues(final ValueTransformerSupplier<? super K, ? super V, ? extends VR> valueTransformerSupplier,final String... stateStoreNames);
KStream	<VO, VR> KStream<K, VR> join(final KStream<K, VO> otherStream, final ValueJoiner<? super V, ? super VO, ? extends VR> joiner, final JoinWindows windows);	<VO, VR> KStream<K, VR> join(final KStream<K, VO> otherStream, final ValueJoiner<? super K, ? super V, ? super VO, ? extends VR> joiner, final JoinWindows windows);
KTable	<VR> KTable<K, VR> mapValues(final

ValueMapper<? super V, ? extends VR> mapper);

<VR>

KStream<

KTable<K, VR> mapValues(final ValueMapper<? super K, ? super V, ? extends VR> mapper);

KStream

KTable

<VO, VR>

KStream<

KTable<K, VR>

transformValues

join(final

ValueTransformerSupplier<? super V, ? extends VR

KTable<K, VO>

valueTransformerSupplier

other, final

String... stateStoreNames);<VR> KStream<K, VR> transformValues(final ValueTransformerSupplier<? super K

ValueJoiner<? super V, ? super

V

VO, ? extends VR>

valueTransformerSupplier,final String... stateStoreNames

joiner);

KStream

<VO, VR>

KStream<

KTable<K, VR> join(final

KStream<

KTable<K, VO>

otherStream

other,

final ValueJoiner<? super K, ? super V, ? super VO, ? extends

VR> joiner,

final JoinWindows windows);

<VO, VR> KStream<K, VR> join(final KStream<K, VO> otherStream,

final ValueJoiner<? super K, ? super V, ? super VO, ? extends VR> joiner,

final JoinWindows windows);

KTable

<VR> KTable<K, VR> mapValues(final ValueMapper<? super V, ? extends VR> mapper);

<VR> KTable<K, VR> mapValues(final ValueMapper<? super K, ? super V, ? extends VR> mapper);KTable

<VO, VR> KTable<K, VR> join(final KTable<K, VO> other, final ValueJoiner<? super V, ? super VO, ? extends VR> joiner);

<VO, VR> KTable<K, VR> join(final KTable<K, VO> other, final ValueJoiner<? super K, ? super V, ? super VO, ? extends VR> joiner);

VR> joiner);

Lacking performance because deep-copy and need for RichFunctions

We extend the target interfaces ValueJoiner, ValueTransformer, and ValueMapper as ValueJoinerWithKey, ValueTransformerWithKey, and ValueMapperWithKey. In extended abstract classes we have an access to keys.

In Processor we check the actual instance of object:

this.valueTransformer = valueTransformer;
if (valueTransformer instanceof ValueTransformerWithKey) {
isTransformerWithKey = true;
} else {
isTransformerWithKey = false;
}

..............

@Override
public void process(K key, V value) {
if (isTransformerWithKey) {
K keyCopy = (K) Utils.deepCopy(key);
  context.forward(key, ((ValueTransformerWithKey<K, V, R>) valueTransformer).transform(keyCopy, value));
  } else {
context.forward(key, valueTransformer.transform(value));
  }
}

As we can see from the above code snippet, we can guard the key change in Processors by deeply copying the object before calling the apply() method.

Space shortcuts

Child pages

Versions Compared

Old Version 8

New Version Current

Key

Motivation

Public Changes

`KStream` interface:

Test Plan

Rejected Alternatives

Not backward-compatible

`KTable` interface:

`KGroupedStream` interface:

Handling lambdas

Handling withKey interfaces while building the topology

Test Plan

Rejected Alternatives

Lambdas are not supported

Not backward-compatible

Lacking performance because deep-copy and need for RichFunctions

Space shortcuts

Child pages

Page History

Versions Compared

Old Version 8

New Version Current

Key

Motivation

Public Changes

KStream interface:

Test Plan

Rejected Alternatives

Not backward-compatible

KTable interface:

KGroupedStream interface:

Handling lambdas

Handling withKey interfaces while building the topology

Test Plan

Rejected Alternatives

Lambdas are not supported

Not backward-compatible

Lacking performance because deep-copy and need for RichFunctions

`KStream` interface:

`KTable` interface:

`KGroupedStream` interface: