org.apache.kafka.streams.kstream

Interface KGroupedStream<K,V>

Type Parameters:

K - Type of keys

V - Type of values

@InterfaceStability.Unstable
public interface KGroupedStream<K,V>

KGroupedStream is an abstraction of a grouped record stream of KeyValue pairs. It is an intermediate representation of a KStream in order to apply an aggregation operation on the original KStream records.

It is an intermediate representation after a grouping of a KStream before an aggregation is applied to the new partitions resulting in a KTable.

A KGroupedStream must be obtained from a KStream via groupByKey() or groupBy(...).

See Also:

KStream

Method Summary

Methods

Modifier and Type	Method and Description
<T> KTable<Windowed<K>,T>	aggregate(Initializer<T> initializer, Aggregator<? super K,? super V,T> aggregator, Merger<? super K,T> sessionMerger, SessionWindows sessionWindows, Serde<T> aggValueSerde, StateStoreSupplier<SessionStore> storeSupplier) Aggregate the values of records in this stream by the grouped key and defined SessionWindows.
<T> KTable<Windowed<K>,T>	aggregate(Initializer<T> initializer, Aggregator<? super K,? super V,T> aggregator, Merger<? super K,T> sessionMerger, SessionWindows sessionWindows, Serde<T> aggValueSerde, String storeName) Aggregate the values of records in this stream by the grouped key and defined SessionWindows.
<VR> KTable<K,VR>	aggregate(Initializer<VR> initializer, Aggregator<? super K,? super V,VR> aggregator, Serde<VR> aggValueSerde, String storeName) Aggregate the values of records in this stream by the grouped key.
<VR> KTable<K,VR>	aggregate(Initializer<VR> initializer, Aggregator<? super K,? super V,VR> aggregator, StateStoreSupplier<KeyValueStore> storeSupplier) Aggregate the values of records in this stream by the grouped key.
<W extends Window,VR> KTable<Windowed<K>,VR>	aggregate(Initializer<VR> initializer, Aggregator<? super K,? super V,VR> aggregator, Windows<W> windows, Serde<VR> aggValueSerde, String storeName) Aggregate the values of records in this stream by the grouped key and defined windows.
<W extends Window,VR> KTable<Windowed<K>,VR>	aggregate(Initializer<VR> initializer, Aggregator<? super K,? super V,VR> aggregator, Windows<W> windows, StateStoreSupplier<WindowStore> storeSupplier) Aggregate the values of records in this stream by the grouped key and defined windows.
KTable<Windowed<K>,Long>	count(SessionWindows sessionWindows, StateStoreSupplier<SessionStore> storeSupplier) Count the number of records in this stream by the grouped key into SessionWindows.
KTable<Windowed<K>,Long>	count(SessionWindows sessionWindows, String storeName) Count the number of records in this stream by the grouped key into SessionWindows.
KTable<K,Long>	count(StateStoreSupplier<KeyValueStore> storeSupplier) Count the number of records in this stream by the grouped key.
KTable<K,Long>	count(String storeName) Count the number of records in this stream by the grouped key.
<W extends Window> KTable<Windowed<K>,Long>	count(Windows<W> windows, StateStoreSupplier<WindowStore> storeSupplier) Count the number of records in this stream by the grouped key and the defined windows.
<W extends Window> KTable<Windowed<K>,Long>	count(Windows<W> windows, String storeName) Count the number of records in this stream by the grouped key and the defined windows.
KTable<Windowed<K>,V>	reduce(Reducer<V> reducer, SessionWindows sessionWindows, StateStoreSupplier<SessionStore> storeSupplier) Combine values of this stream by the grouped key into SessionWindows.
KTable<Windowed<K>,V>	reduce(Reducer<V> reducer, SessionWindows sessionWindows, String storeName) Combine values of this stream by the grouped key into SessionWindows.
KTable<K,V>	reduce(Reducer<V> reducer, StateStoreSupplier<KeyValueStore> storeSupplier) Combine the value of records in this stream by the grouped key.
KTable<K,V>	reduce(Reducer<V> reducer, String storeName) Combine the values of records in this stream by the grouped key.
<W extends Window> KTable<Windowed<K>,V>	reduce(Reducer<V> reducer, Windows<W> windows, StateStoreSupplier<WindowStore> storeSupplier) Combine the values of records in this stream by the grouped key and the defined windows.
<W extends Window> KTable<Windowed<K>,V>	reduce(Reducer<V> reducer, Windows<W> windows, String storeName) Combine the number of records in this stream by the grouped key and the defined windows.

Method Detail

count

KTable<K,Long> count(String storeName)

Count the number of records in this stream by the grouped key. Records with null key or value are ignored. The result is written into a local KeyValueStore (which is basically an ever-updating materialized view) that can be queried using the provided storeName. Furthermore, updates to the store are sent downstream into a KTable changelog stream.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local KeyValueStore it must be obtained via KafkaStreams#store(...):

KafkaStreams streams = ... // counting words
 ReadOnlyKeyValueStore<String,Long> localStore = streams.store(storeName, QueryableStoreTypes.<String, Long>keyValueStore());
 String key = "some-word";
 Long countForWord = localStore.get(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka. The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide storeName, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

Parameters:

storeName - the name of the underlying KTable state store

Returns:

a KTable that contains "update" records with unmodified keys and Long values that represent the latest (rolling) count (i.e., number of records) for each key

count

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

Count the number of records in this stream by the grouped key. Records with null key or value are ignored. The result is written into a local KeyValueStore (which is basically an ever-updating materialized view) provided by the given storeSupplier. Furthermore, updates to the store are sent downstream into a KTable changelog stream.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local KeyValueStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // counting words
 String storeName = storeSupplier.name();
 ReadOnlyKeyValueStore<String,Long> localStore = streams.store(storeName, QueryableStoreTypes.<String, Long>keyValueStore());
 String key = "some-word";
 Long countForWord = localStore.get(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Parameters:

storeSupplier - user defined state store supplier

Returns:

a KTable that contains "update" records with unmodified keys and Long values that represent the latest (rolling) count (i.e., number of records) for each key

count

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

Count the number of records in this stream by the grouped key and the defined windows. Records with null key or value are ignored. The specified windows define either hopping time windows that can be overlapping or tumbling (c.f. TimeWindows) or they define landmark windows (c.f. UnlimitedWindows). The result is written into a local windowed KeyValueStore (which is basically an ever-updating materialized view) that can be queried using the provided storeName. Windows are retained until their retention time expires (c.f. Windows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local windowed KeyValueStore it must be obtained via KafkaStreams#store(...):

KafkaStreams streams = ... // counting words
 ReadOnlyWindowStore<String,Long> localWindowStore = streams.store(storeName, QueryableStoreTypes.<String, Long>windowStore());
 String key = "some-word";
 long fromTime = ...;
 long toTime = ...;
 WindowStoreIterator<Long> countForWordsForWindows = localWindowStore.fetch(key, timeFrom, timeTo); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka. The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide storeName, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

Parameters:

windows - the specification of the aggregation Windows

storeName - the name of the underlying KTable state store

Returns:

a windowed KTable that contains "update" records with unmodified keys and Long values that represent the latest (rolling) count (i.e., number of records) for each key within a window

count

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

Count the number of records in this stream by the grouped key and the defined windows. Records with null key or value are ignored. The specified windows define either hopping time windows that can be overlapping or tumbling (c.f. TimeWindows) or they define landmark windows (c.f. UnlimitedWindows). The result is written into a local windowed KeyValueStore (which is basically an ever-updating materialized view) provided by the given storeSupplier. Windows are retained until their retention time expires (c.f. Windows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local windowed KeyValueStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // counting words
 String storeName = storeSupplier.name();
 ReadOnlyWindowStore<String,Long> localWindowStore = streams.store(storeName, QueryableStoreTypes.<String, Long>windowStore());
 String key = "some-word";
 long fromTime = ...;
 long toTime = ...;
 WindowStoreIterator<Long> countForWordsForWindows = localWindowStore.fetch(key, timeFrom, timeTo); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Parameters:

windows - the specification of the aggregation Windows

storeSupplier - user defined state store supplier

Returns:

a windowed KTable that contains "update" records with unmodified keys and Long values that represent the latest (rolling) count (i.e., number of records) for each key within a window

count

KTable<Windowed<K>,Long> count(SessionWindows sessionWindows,
                             String storeName)

Count the number of records in this stream by the grouped key into SessionWindows. Records with null key or value are ignored. The result is written into a local SessionStore (which is basically an ever-updating materialized view) that can be queried using the provided storeName. SessionWindows are retained until their retention time expires (c.f. SessionWindows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local SessionStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // counting words
 String storeName = storeSupplier.name();
 ReadOnlySessionStore<String,Long> sessionStore = streams.store(storeName, QueryableStoreTypes.<String, Long>sessionStore());
 String key = "some-word";
 KeyValueIterator<Windowed<String>, Long> iterator = sessionStore.fetch(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Parameters:

sessionWindows - the specification of the aggregation SessionWindows

storeName - the name of the state store created from this operation.

Returns:

a windowed KTable that contains "update" records with unmodified keys and Long values that represent the latest (rolling) count (i.e., number of records) for each key within a window

count

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

Count the number of records in this stream by the grouped key into SessionWindows. Records with null key or value are ignored. The result is written into a local SessionStore (which is basically an ever-updating materialized view) provided by the given storeSupplier. SessionWindows are retained until their retention time expires (c.f. SessionWindows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local SessionStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // counting words
 String storeName = storeSupplier.name();
 ReadOnlySessionStore<String,Long> sessionStore = streams.store(storeName, QueryableStoreTypes.<String, Long>sessionStore());
 String key = "some-word";
 KeyValueIterator<Windowed<String>, Long> iterator = sessionStore.fetch(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Parameters:

sessionWindows - the specification of the aggregation SessionWindows

storeSupplier - user defined state store supplier

Returns:

a windowed KTable that contains "update" records with unmodified keys and Long values that represent the latest (rolling) count (i.e., number of records) for each key within a window

reduce

KTable<K,V> reduce(Reducer<V> reducer,
                 String storeName)

Combine the values of records in this stream by the grouped key. Records with null key or value are ignored. Combining implies that the type of the aggregate result is the same as the type of the input value (c.f. aggregate(Initializer, Aggregator, Serde, String)). The result is written into a local KeyValueStore (which is basically an ever-updating materialized view) that can be queried using the provided storeName. Furthermore, updates to the store are sent downstream into a KTable changelog stream.

The specified Reducer is applied for each input record and computes a new aggregate using the current aggregate and the record's value. If there is no current aggregate the Reducer is not applied and the new aggregate will be the record's value as-is. Thus, reduce(Reducer, String) can be used to compute aggregate functions like sum, min, or max.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local KeyValueStore it must be obtained via KafkaStreams#store(...):

KafkaStreams streams = ... // compute sum
 ReadOnlyKeyValueStore<String,Long> localStore = streams.store(storeName, QueryableStoreTypes.<String, Long>keyValueStore());
 String key = "some-key";
 Long sumForKey = localStore.get(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka. The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide storeName, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

Parameters:

reducer - a Reducer that computes a new aggregate result

storeName - the name of the underlying KTable state store

Returns:

a KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key

reduce

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

Combine the value of records in this stream by the grouped key. Records with null key or value are ignored. Combining implies that the type of the aggregate result is the same as the type of the input value (c.f. aggregate(Initializer, Aggregator, StateStoreSupplier)). The result is written into a local KeyValueStore (which is basically an ever-updating materialized view) provided by the given storeSupplier. Furthermore, updates to the store are sent downstream into a KTable changelog stream.

The specified Reducer is applied for each input record and computes a new aggregate using the current aggregate and the record's value. If there is no current aggregate the Reducer is not applied and the new aggregate will be the record's value as-is. Thus, reduce(Reducer, StateStoreSupplier) can be used to compute aggregate functions like sum, min, or max.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local KeyValueStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // compute sum
 String storeName = storeSupplier.name();
 ReadOnlyKeyValueStore<String,Long> localStore = streams.store(storeName, QueryableStoreTypes.<String, Long>keyValueStore());
 String key = "some-key";
 Long sumForKey = localStore.get(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Parameters:

reducer - a Reducer that computes a new aggregate result

storeSupplier - user defined state store supplier

Returns:

a KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key

reduce

<W extends Window> KTable<Windowed<K>,V> reduce(Reducer<V> reducer,
                                              Windows<W> windows,
                                              String storeName)

Combine the number of records in this stream by the grouped key and the defined windows. Records with null key or value are ignored. Combining implies that the type of the aggregate result is the same as the type of the input value (c.f. aggregate(Initializer, Aggregator, Windows, Serde, String)). The specified windows define either hopping time windows that can be overlapping or tumbling (c.f. TimeWindows) or they define landmark windows (c.f. UnlimitedWindows). The result is written into a local windowed KeyValueStore (which is basically an ever-updating materialized view) that can be queried using the provided storeName. Windows are retained until their retention time expires (c.f. Windows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

The specified Reducer is applied for each input record and computes a new aggregate using the current aggregate and the record's value. If there is no current aggregate the Reducer is not applied and the new aggregate will be the record's value as-is. Thus, reduce(Reducer, Windows, String) can be used to compute aggregate functions like sum, min, or max.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local windowed KeyValueStore it must be obtained via KafkaStreams#store(...):

KafkaStreams streams = ... // compute sum
 ReadOnlyWindowStore<String,Long> localWindowStore = streams.store(storeName, QueryableStoreTypes.<String, Long>windowStore());
 String key = "some-key";
 long fromTime = ...;
 long toTime = ...;
 WindowStoreIterator<Long> sumForKeyForWindows = localWindowStore.fetch(key, timeFrom, timeTo); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka. The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide storeName, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

Parameters:

reducer - a Reducer that computes a new aggregate result

windows - the specification of the aggregation Windows

storeName - the name of the state store created from this operation

Returns:

a windowed KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key within a window

reduce

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

Combine the values of records in this stream by the grouped key and the defined windows. Records with null key or value are ignored. Combining implies that the type of the aggregate result is the same as the type of the input value (c.f. aggregate(Initializer, Aggregator, Windows, Serde, String)). The specified windows define either hopping time windows that can be overlapping or tumbling (c.f. TimeWindows) or they define landmark windows (c.f. UnlimitedWindows). The result is written into a local windowed KeyValueStore (which is basically an ever-updating materialized view) provided by the given storeSupplier. Windows are retained until their retention time expires (c.f. Windows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

The specified Reducer is applied for each input record and computes a new aggregate using the current aggregate and the record's value. If there is no current aggregate the Reducer is not applied and the new aggregate will be the record's value as-is. Thus, reduce(Reducer, Windows, StateStoreSupplier) can be used to compute aggregate functions like sum, min, or max.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local windowed KeyValueStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // compute sum
 Sting storeName = storeSupplier.name();
 ReadOnlyWindowStore<String,Long> localWindowStore = streams.store(storeName, QueryableStoreTypes.<String, Long>windowStore());
 String key = "some-key";
 long fromTime = ...;
 long toTime = ...;
 WindowStoreIterator<Long> sumForKeyForWindows = localWindowStore.fetch(key, timeFrom, timeTo); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Parameters:

reducer - a Reducer that computes a new aggregate result

windows - the specification of the aggregation Windows

storeSupplier - user defined state store supplier

Returns:

a windowed KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key within a window

reduce

KTable<Windowed<K>,V> reduce(Reducer<V> reducer,
                           SessionWindows sessionWindows,
                           String storeName)

Combine values of this stream by the grouped key into SessionWindows. Records with null key or value are ignored. Combining implies that the type of the aggregate result is the same as the type of the input value (c.f. aggregate(Initializer, Aggregator, Merger, SessionWindows, Serde, String)). The result is written into a local SessionStore (which is basically an ever-updating materialized view) that can be queried using the provided storeName. SessionWindows are retained until their retention time expires (c.f. SessionWindows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

The specified Reducer is applied for each input record and computes a new aggregate using the current aggregate and the record's value. If there is no current aggregate the Reducer is not applied and the new aggregate will be the record's value as-is. Thus, reduce(Reducer, SessionWindows, String) can be used to compute aggregate functions like sum, min, or max.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local SessionStore it must be obtained via KafkaStreams#store(...):

KafkaStreams streams = ... // compute sum
 ReadOnlySessionStore<String,Long> sessionStore = streams.store(storeName, QueryableStoreTypes.<String, Long>sessionStore());
 String key = "some-key";
 KeyValueIterator<Windowed<String>, Long> sumForKeyForSession = localWindowStore.fetch(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka. The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide storeName, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

Parameters:

reducer - the instance of Reducer

sessionWindows - the specification of the aggregation SessionWindows

storeName - the name of the state store created from this operation

Returns:

a windowed KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key within a window

reduce

KTable<Windowed<K>,V> reduce(Reducer<V> reducer,
                           SessionWindows sessionWindows,
                           StateStoreSupplier<SessionStore> storeSupplier)

Combine values of this stream by the grouped key into SessionWindows. Records with null key or value are ignored. Combining implies that the type of the aggregate result is the same as the type of the input value (c.f. aggregate(Initializer, Aggregator, Merger, SessionWindows, Serde, String)). The result is written into a local SessionStore (which is basically an ever-updating materialized view) provided by the given storeSupplier. SessionWindows are retained until their retention time expires (c.f. SessionWindows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

The specified Reducer is applied for each input record and computes a new aggregate using the current aggregate and the record's value. If there is no current aggregate the Reducer is not applied and the new aggregate will be the record's value as-is. Thus, reduce(Reducer, SessionWindows, StateStoreSupplier) can be used to compute aggregate functions like sum, min, or max.

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local SessionStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // compute sum
 Sting storeName = storeSupplier.name();
 ReadOnlySessionStore<String,Long> sessionStore = streams.store(storeName, QueryableStoreTypes.<String, Long>sessionStore());
 String key = "some-key";
 KeyValueIterator<Windowed<String>, Long> sumForKeyForSession = localWindowStore.fetch(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka. The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide storeName, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

Parameters:

reducer - the instance of Reducer

sessionWindows - the specification of the aggregation SessionWindows

storeSupplier - user defined state store supplier

Returns:

a windowed KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key within a window

aggregate

<VR> KTable<K,VR> aggregate(Initializer<VR> initializer,
                          Aggregator<? super K,? super V,VR> aggregator,
                          Serde<VR> aggValueSerde,
                          String storeName)

Aggregate the values of records in this stream by the grouped key. Records with null key or value are ignored. Aggregating is a generalization of combining via reduce(...) as it, for example, allows the result to have a different type than the input values. The result is written into a local KeyValueStore (which is basically an ever-updating materialized view) that can be queried using the provided storeName. Furthermore, updates to the store are sent downstream into a KTable changelog stream.

The specified Initializer is applied once directly before the first input record is processed to provide an initial intermediate aggregation result that is used to process the first record. The specified Aggregator is applied for each input record and computes a new aggregate using the current aggregate (or for the very first record using the intermediate aggregation result provided via the Initializer) and the record's value. Thus, aggregate(Initializer, Aggregator, Serde, String) can be used to compute aggregate functions like count (c.f. count(String)).

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local KeyValueStore it must be obtained via KafkaStreams#store(...):

KafkaStreams streams = ... // some aggregation on value type double
 ReadOnlyKeyValueStore<String,Long> localStore = streams.store(storeName, QueryableStoreTypes.<String, Long>keyValueStore());
 String key = "some-key";
 Long aggForKey = localStore.get(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka. The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide storeName, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

Type Parameters:

VR - the value type of the resulting KTable

Parameters:

initializer - an Initializer that computes an initial intermediate aggregation result

aggregator - an Aggregator that computes a new aggregate result

aggValueSerde - aggregate value serdes for materializing the aggregated table, if not specified the default serdes defined in the configs will be used

storeName - the name of the state store created from this operation

Returns:

a KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key

aggregate

<VR> KTable<K,VR> aggregate(Initializer<VR> initializer,
                          Aggregator<? super K,? super V,VR> aggregator,
                          StateStoreSupplier<KeyValueStore> storeSupplier)

Aggregate the values of records in this stream by the grouped key. Records with null key or value are ignored. Aggregating is a generalization of combining via reduce(...) as it, for example, allows the result to have a different type than the input values. The result is written into a local KeyValueStore (which is basically an ever-updating materialized view) provided by the given storeSupplier. Furthermore, updates to the store are sent downstream into a KTable changelog stream.

The specified Initializer is applied once directly before the first input record is processed to provide an initial intermediate aggregation result that is used to process the first record. The specified Aggregator is applied for each input record and computes a new aggregate using the current aggregate (or for the very first record using the intermediate aggregation result provided via the Initializer) and the record's value. Thus, aggregate(Initializer, Aggregator, StateStoreSupplier) can be used to compute aggregate functions like count (c.f. count(String)).

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local KeyValueStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // some aggregation on value type double
 Sting storeName = storeSupplier.name();
 ReadOnlyKeyValueStore<String,Long> localStore = streams.store(storeName, QueryableStoreTypes.<String, Long>keyValueStore());
 String key = "some-key";
 Long aggForKey = localStore.get(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Type Parameters:

VR - the value type of the resulting KTable

Parameters:

initializer - an Initializer that computes an initial intermediate aggregation result

aggregator - an Aggregator that computes a new aggregate result

storeSupplier - user defined state store supplier

Returns:

a KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key

aggregate

<W extends Window,VR> KTable<Windowed<K>,VR> aggregate(Initializer<VR> initializer,
                                                     Aggregator<? super K,? super V,VR> aggregator,
                                                     Windows<W> windows,
                                                     Serde<VR> aggValueSerde,
                                                     String storeName)

Aggregate the values of records in this stream by the grouped key and defined windows. Records with null key or value are ignored. Aggregating is a generalization of combining via reduce(...) as it, for example, allows the result to have a different type than the input values. The specified windows define either hopping time windows that can be overlapping or tumbling (c.f. TimeWindows) or they define landmark windows (c.f. UnlimitedWindows). The result is written into a local windowed KeyValueStore (which is basically an ever-updating materialized view) that can be queried using the provided storeName. Windows are retained until their retention time expires (c.f. Windows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

The specified Initializer is applied once per window directly before the first input record is processed to provide an initial intermediate aggregation result that is used to process the first record. The specified Aggregator is applied for each input record and computes a new aggregate using the current aggregate (or for the very first record using the intermediate aggregation result provided via the Initializer) and the record's value. Thus, aggregate(Initializer, Aggregator, Windows, Serde, String) can be used to compute aggregate functions like count (c.f. count(String)).

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local windowed KeyValueStore it must be obtained via KafkaStreams#store(...):

KafkaStreams streams = ... // some windowed aggregation on value type double
 ReadOnlyWindowStore<String,Long> localWindowStore = streams.store(storeName, QueryableStoreTypes.<String, Long>windowStore());
 String key = "some-key";
 long fromTime = ...;
 long toTime = ...;
 WindowStoreIterator<Long> aggForKeyForWindows = localWindowStore.fetch(key, timeFrom, timeTo); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka. The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide storeName, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

Type Parameters:

VR - the value type of the resulting KTable

Parameters:

initializer - an Initializer that computes an initial intermediate aggregation result

aggregator - an Aggregator that computes a new aggregate result

windows - the specification of the aggregation Windows

aggValueSerde - aggregate value serdes for materializing the aggregated table, if not specified the default serdes defined in the configs will be used

storeName - the name of the state store created from this operation

Returns:

a windowed KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key within a window

aggregate

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

Aggregate the values of records in this stream by the grouped key and defined windows. Records with null key or value are ignored. Aggregating is a generalization of combining via reduce(...) as it, for example, allows the result to have a different type than the input values. The specified windows define either hopping time windows that can be overlapping or tumbling (c.f. TimeWindows) or they define landmark windows (c.f. UnlimitedWindows). The result is written into a local windowed KeyValueStore (which is basically an ever-updating materialized view) provided by the given storeSupplier. Windows are retained until their retention time expires (c.f. Windows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

The specified Initializer is applied once per window directly before the first input record is processed to provide an initial intermediate aggregation result that is used to process the first record. The specified Aggregator is applied for each input record and computes a new aggregate using the current aggregate (or for the very first record using the intermediate aggregation result provided via the Initializer) and the record's value. Thus, aggregate(Initializer, Aggregator, Windows, StateStoreSupplier) can be used to compute aggregate functions like count (c.f. count(String)).

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local windowed KeyValueStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // some windowed aggregation on value type Long
 Sting storeName = storeSupplier.name();
 ReadOnlyWindowStore<String,Long> localWindowStore = streams.store(storeName, QueryableStoreTypes.<String, Long>windowStore());
 String key = "some-key";
 long fromTime = ...;
 long toTime = ...;
 WindowStoreIterator<Long> aggForKeyForWindows = localWindowStore.fetch(key, timeFrom, timeTo); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Type Parameters:

VR - the value type of the resulting KTable

Parameters:

initializer - an Initializer that computes an initial intermediate aggregation result

aggregator - an Aggregator that computes a new aggregate result

windows - the specification of the aggregation Windows

storeSupplier - user defined state store supplier

Returns:

a windowed KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key within a window

aggregate

<T> KTable<Windowed<K>,T> aggregate(Initializer<T> initializer,
                                  Aggregator<? super K,? super V,T> aggregator,
                                  Merger<? super K,T> sessionMerger,
                                  SessionWindows sessionWindows,
                                  Serde<T> aggValueSerde,
                                  String storeName)

Aggregate the values of records in this stream by the grouped key and defined SessionWindows. Records with null key or value are ignored. Aggregating is a generalization of combining via reduce(...) as it, for example, allows the result to have a different type than the input values. The result is written into a local SessionStore (which is basically an ever-updating materialized view) that can be queried using the provided storeName. SessionWindows are retained until their retention time expires (c.f. SessionWindows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

The specified Initializer is applied once per session directly before the first input record is processed to provide an initial intermediate aggregation result that is used to process the first record. The specified Aggregator is applied for each input record and computes a new aggregate using the current aggregate (or for the very first record using the intermediate aggregation result provided via the Initializer) and the record's value. Thus, aggregate(Initializer, Aggregator, Merger, SessionWindows, Serde, String) can be used to compute aggregate functions like count (c.f. count(String))

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local SessionStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // some windowed aggregation on value type double
 Sting storeName = storeSupplier.name();
 ReadOnlySessionStore<String, Long> sessionStore = streams.store(storeName, QueryableStoreTypes.<String, Long>sessionStore());
 String key = "some-key";
 KeyValueIterator<Windowed<String>, Long> aggForKeyForSession = localWindowStore.fetch(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Type Parameters:

T - the value type of the resulting KTable

Parameters:

initializer - the instance of Initializer

aggregator - the instance of Aggregator

sessionMerger - the instance of Merger

sessionWindows - the specification of the aggregation SessionWindows

aggValueSerde - aggregate value serdes for materializing the aggregated table, if not specified the default serdes defined in the configs will be used

storeName - the name of the state store created from this operation

Returns:

a windowed KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key within a window

aggregate

<T> KTable<Windowed<K>,T> aggregate(Initializer<T> initializer,
                                  Aggregator<? super K,? super V,T> aggregator,
                                  Merger<? super K,T> sessionMerger,
                                  SessionWindows sessionWindows,
                                  Serde<T> aggValueSerde,
                                  StateStoreSupplier<SessionStore> storeSupplier)

Aggregate the values of records in this stream by the grouped key and defined SessionWindows. Records with null key or value are ignored. Aggregating is a generalization of combining via reduce(...) as it, for example, allows the result to have a different type than the input values. The result is written into a local SessionStore (which is basically an ever-updating materialized view) provided by the given storeSupplier. SessionWindows are retained until their retention time expires (c.f. SessionWindows.until(long)). Furthermore, updates to the store are sent downstream into a windowed KTable changelog stream, where "windowed" implies that the KTable key is a combined key of the original record key and a window ID.

The specified Initializer is applied once per session directly before the first input record is processed to provide an initial intermediate aggregation result that is used to process the first record. The specified Aggregator is applied for each input record and computes a new aggregate using the current aggregate (or for the very first record using the intermediate aggregation result provided via the Initializer) and the record's value. Thus, #aggregate(Initializer, Aggregator, Merger, SessionWindows, Serde, StateStoreSupplier) can be used to compute aggregate functions like count (c.f. count(String)).

Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to the same window and key. The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of parallel running Kafka Streams instances, and the configuration parameters for cache size, and commit intervall.

To query the local SessionStore it must be obtained via KafkaStreams#store(...). Use StateStoreSupplier.name() to get the store name:

KafkaStreams streams = ... // some windowed aggregation on value type double
 Sting storeName = storeSupplier.name();
 ReadOnlySessionStore<String, Long> sessionStore = streams.store(storeName, QueryableStoreTypes.<String, Long>sessionStore());
 String key = "some-key";
 KeyValueIterator<Windowed<String>, Long> aggForKeyForSession = localWindowStore.fetch(key); // key must be local (application state is shared over all running Kafka Streams instances)
 

For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.allMetadata() to query the value of the key on a parallel running instance of your Kafka Streams application.

Type Parameters:

T - the value type of the resulting KTable

Parameters:

initializer - the instance of Initializer

aggregator - the instance of Aggregator

sessionMerger - the instance of Merger

sessionWindows - the specification of the aggregation SessionWindows

aggValueSerde - aggregate value serdes for materializing the aggregated table, if not specified the default serdes defined in the configs will be used

storeSupplier - user defined state store supplier

Returns:

a windowed KTable that contains "update" records with unmodified keys, and values that represent the latest (rolling) aggregate for each key within a window