Status

Current state: "Under Discussion"

Discussion thread: here

JIRA: TBD

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

Motivation

The recommended practice to create a StateStoreSupplier is as per the following example:

StateStoreSupplier countStore = Stores.create("Counts")
    .withKeys(Serdes.String())
    .withValues(Serdes.Long())
    .persistent()
    .build();

However, StateStoreSupplier is a generic interface that takes the StateStore type as a parameter:

public interface StateStoreSupplier<T extends StateStore>

In the above example that type parameter is lost as the build() method returns a raw type.

As StateStoreSupplier is passed to count/reduce/aggregate etc. methods on KGroupedStream or KGroupedTable, the compiler cannot detect if a supplier for the wrong kind of store is provided.

The other parameters to those methods, such as Serdes, Reducers, etc are type-parameterised by the key and value types allowing compile-time type checks.

The StateStoreSupplier argument stands out as a raw type. Making it type-parameterised will help detect at compile time errors such as when someone refactors their app to use a different typo of aggregations (e.g. TimeWindowed vs SessionWindowed) and forgets to change the StateStoreSupplier passed in.

Public Interfaces

• KGroupedStream

  • KTable<K, Long> count(final StateStoreSupplier<KeyValueStore<K, Long>> storeSupplier);

  • <W extends Window> KTable<Windowed<K>, Long> count(final Windows<W> windows,
                                                                                                   final StateStoreSupplier<WindowStore<K, Long>> storeSupplier);

  • KTable<Windowed<K>, Long> count(final SessionWindows sessionWindows,
                                                                final StateStoreSupplier<SessionStore<K, Long>> storeSupplier);
    
    

  • KTable<K, V> reduce(final Reducer<V> reducer,
                                       final StateStoreSupplier<KeyValueStore<K ,V>> storeSupplier);
    
    

  • <W extends Window> KTable<Windowed<K>, V> reduce(final Reducer<V> reducer,
                                                                                                final Windows<W> windows,
                                                                                                final StateStoreSupplier<WindowStore<K, V>> storeSupplier);
    
    

  • KTable<Windowed<K>, V> reduce(final Reducer<V> reducer,
                                                            final SessionWindows sessionWindows,

                                                            final StateStoreSupplier<SessionStore<K, V>> storeSupplier);
    
    

  • <VR> KTable<K, VR> aggregate(final Initializer<VR> initializer,
                                                         final Aggregator<? super K, ? super V, VR> aggregator,

                                                         final StateStoreSupplier<KeyValueStore<K, VR>> storeSupplier);

  • <W extends Window, VR> KTable<Windowed<K>, VR> aggregate(final Initializer<VR> initializer,
                                                                                                               final Aggregator<? super K, ? super V, VR> aggregator,
                                                                                                               final Windows<W> windows,
                                                                                                               final StateStoreSupplier<WindowStore<K, VR>> storeSupplier);

  • <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<K, T>> storeSupplier);

• KGroupedTable

  • KTable<K, Long> count(final StateStoreSupplier<KeyValueStore<K, Long>> storeSupplier);

     

  • KTable<K, V> reduce(final Reducer<V> adder,
                                       final Reducer<V> subtractor,
                                       final StateStoreSupplier<KeyValueStore<K, V>> storeSupplier);

     

  • <VR> KTable<K, VR> aggregate(final Initializer<VR> initializer,
                                                         final Aggregator<? super K, ? super V, VR> adder,
                                                         final Aggregator<? super K, ? super V, VR> subtractor,
                                                         final StateStoreSupplier<KeyValueStore<K, VR>> storeSupplier);

• Stores
  • 2 new public interfaces:

    • public interface PersistentWindowFactory<K, V> {
      
      
      /**
      * Caching should be enabled on the created store.
      * @return the factory to create a persistent window store
      */
      PersistentWindowFactory<K, V> enableCaching();
      
      /**
      * Indicates that a changelog should not be created for the key-value store
      * @return the factory to create a persistent window store
      */
      PersistentWindowFactory<K, V> disableLogging();
      
      /**
      * Indicates that a changelog should be created for the store. The changelog will be created
      * with the provided cleanupPolicy and configs.
      *
      * Note: Any unrecognized configs will be ignored.
      * @param config any configs that should be applied to the changelog
      * @return the factory to create a persistent window store
      */
      PersistentWindowFactory<K, V> enableLogging(final Map<String, String> config);
      
      
      /**
      * Return the instance of StateStoreSupplier of new window store.
      * @return the key-value store; never null
      */
      StateStoreSupplier<WindowStore<K, V>> build();
      }

    • public interface PersistentSessionFactory<K, V> {
      /**
      * Indicates that a changelog should be created for the store. The changelog will be created
      * with the provided cleanupPolicy and configs.
      *
      * Note: Any unrecognized configs will be ignored.
      * @param config any configs that should be applied to the changelog
      * @return the factory to create a persistent key-value store
      */
      PersistentSessionFactory<K, V> enableLogging(final Map<String, String> config);
      /**
      * Indicates that a changelog should not be created for the key-value store
      * @return the factory to create a persistent session store
      */
      PersistentSessionFactory<K, V> disableLogging();
      /**
      * Caching should be enabled on the created store.
      * @return the factory to create a persistent session store
      */
      PersistentSessionFactory<K, V> enableCaching();
      /**
      * Return the instance of StateStoreSupplier of new session store.
      * @return the key-value store; never null
      */
      StateStoreSupplier<SessionStore<K, V>> build();
       
      }

    • changes to PersistentKeyValueFactory :

      • PersistentWindowFactory<K, V> windowed(final long windowSize, long retentionPeriod, int numSegments, boolean retainDuplicates);

      • PersistentSessionFactory<K, V> sessionWindowed(final long retentionPeriod);

      • StateStoreSupplier<KeyValueStore<K, V>> build();

    • changes to InMemoryKeyValueFactory:

      • StateStoreSupplier<KeyValueStore<K, V>> build();

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

To be evaluated

Test Plan

Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Rejected Alternatives

If 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.