...

public synchronized <K, V> KTable<K, V> table(final String topic);
public synchronized <K, V> KTable<K, V> table(final String topic, final Consumed<K, V> consumed);
public synchronized <K, V> KTable<K, V> table(final String topic, final Materialized<K, V, KeyValueStore<Bytes, byte[]>> materialized);
public synchronized <K, V> KTable<K, V> table(final String topic, final Consumed<K, V> consumed, final Materialized<K, V, KeyValueStore<Bytes, byte[]>> materialized);

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

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

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

Through Materialized struct, we could pass in a KeyValueStore<Bytes, byte[]> struct as the local state store. In fact, underlying KTable class by default stores data in a key-value store backed up by RocksDB. We want to also support window store which is a very natural requirement if we are materializing a topic with windowed key.

Proposed Changes

We would like to add 4 new APIs to support window store as underlying storage option.

public synchronized <K, V> KTable<Windowed<K>, V> windowedTable(final String topic);
public synchronized <K, V> KTable<Windowed<K>, V> windowedTable(final String topic, final Consumed<K, V> consumed);
public synchronized <K, V> KTable<Windowed<K>, V> windowedTable(final String topic, final Materialized<K, V, WindowStore<Bytes, byte[]>> materialized);
public synchronized <K, V> KTable<Windowed<K>, V> windowedTable(final String topic, final Consumed<K, V> consumed, final Materialized<K, V, WindowStore<Bytes, byte[]>> materialized);

Compatibility, Deprecation, and Migration Plan

This KIP will not change the existing table() API, which should be backward compatible.

Rejected Alternatives

We start by changing the store type on the table API to support window store:

public synchronized <K, V> KTable<K, V> table(final String topic, final Materialized<K, V, WindowStore<Bytes, byte[]>> materialized);

However, this straightfoward solution hits 2 problems:

1. The store type could not be changed due to Java "method has same erasure" error
2. Even if we name the API to windowedTable, it is still not ideal because we saw certain KTable return type in other classes such as in KGroupedStream:
   
   

<W extends Window> KTable<Windowed<K>, Long> count(final Windows<W> windows, final String queryableStoreName);

So we could see that if we return KTable<K, V> in the above table API for window store, we are introducing inconsistent API to the outside user. By defining the output as KTable<Windowed<K>, V> the user could be clear that we are using window store in the underlying implementationIf 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.