org.apache.kafka.streams.kstream.SessionWindowedKStream Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.kafka.streams.kstream;
import org.apache.kafka.common.utils.Bytes;
import org.apache.kafka.streams.KafkaStreams;
import org.apache.kafka.streams.KeyValue;
import org.apache.kafka.streams.StoreQueryParameters;
import org.apache.kafka.streams.StreamsConfig;
import org.apache.kafka.streams.Topology;
import org.apache.kafka.streams.state.SessionStore;
import java.time.Duration;
/**
* {@code SessionWindowedKStream} is an abstraction of a windowed record stream of {@link KeyValue} pairs.
* It is an intermediate representation after a grouping and windowing of a {@link KStream} before an aggregation is
* applied to the new (partitioned) windows resulting in a windowed {@link KTable} (a windowed
* {@code KTable} is a {@link KTable} with key type {@link Windowed Windowed}).
*
* {@link SessionWindows} are dynamic data driven windows.
* They have no fixed time boundaries, rather the size of the window is determined by the records.
*
* The result is written into a local {@link SessionStore} (which is basically an ever-updating
* materialized view) that can be queried using the name provided in the {@link Materialized} instance.
* Furthermore, updates to the store are sent downstream into a windowed {@link KTable} changelog stream, where
* "windowed" implies that the {@link KTable} key is a combined key of the original record key and a window ID.
* New events are added to sessions until their grace period ends (see {@link SessionWindows#grace(Duration)}).
*
* A {@code SessionWindowedKStream} must be obtained from a {@link KGroupedStream} via
* {@link KGroupedStream#windowedBy(SessionWindows)}.
*
* @param Type of keys
* @param Type of values
* @see KStream
* @see KGroupedStream
* @see SessionWindows
*/
public interface SessionWindowedKStream {
/**
* Count the number of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code null} key or value are ignored.
*
* The result is written into a local {@link SessionStore} (which is basically an ever-updating materialized view).
* The default key serde from the config will be used for serializing the result.
* If a different serde is required then you should use {@link #count(Materialized)}.
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
* Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to
* the same session 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 {@link StreamsConfig configuration} parameters for
* {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* 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 "${applicationId}-${internalStoreName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "internalStoreName" is an internal name
* and "-changelog" is a fixed suffix.
* Note that the internal store name may not be queryable through Interactive Queries.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @return a windowed {@link KTable} that contains "update" records with unmodified keys and {@link Long} values
* that represent the latest (rolling) count (i.e., number of records) for each key per session
*/
KTable, Long> count();
/**
* Count the number of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code null} key or value are ignored.
*
* The result is written into a local {@link SessionStore} (which is basically an ever-updating materialized view).
* The default key serde from the config will be used for serializing the result.
* If a different serde is required then you should use {@link #count(Named, Materialized)}.
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
* Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to
* the same session 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 {@link StreamsConfig configuration} parameters for
* {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* 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 "${applicationId}-${internalStoreName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "internalStoreName" is an internal name
* and "-changelog" is a fixed suffix.
* Note that the internal store name may not be queryable through Interactive Queries.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param named a {@link Named} config used to name the processor in the topology. Cannot be {@code null}.
* @return a windowed {@link KTable} that contains "update" records with unmodified keys and {@link Long} values
* that represent the latest (rolling) count (i.e., number of records) for each key per session
*/
KTable, Long> count(final Named named);
/**
* Count the number of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code null} key or value are ignored.
*
* The result is written into a local {@link SessionStore} (which is basically an ever-updating materialized view)
* that can be queried using the name provided with {@link Materialized}.
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
*
* Not all updates might get sent downstream, as an internal cache will be used to deduplicate consecutive updates
* to the same window and key if caching is enabled on the {@link Materialized} instance.
* When caching is enabled 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 {@link StreamsConfig configuration}
* parameters for {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* To query the local {@link SessionStore} it must be obtained via
* {@link KafkaStreams#store(StoreQueryParameters) KafkaStreams#store(...)}:
*
{@code
* KafkaStreams streams = ... // compute sum
* Sting queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
* ReadOnlySessionStore localWindowStore = streams.store(queryableStoreName, QueryableStoreTypes.ReadOnlySessionStore);
* String key = "some-key";
* KeyValueIterator, Long> sumForKeyForWindows = 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 {@link 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.
* Therefore, the store name defined by the Materialized instance must be a valid Kafka topic name and cannot
* contain characters other than ASCII alphanumerics, '.', '_' and '-'.
* The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "storeName" is the provide store name defined
* in {@code Materialized}, and "-changelog" is a fixed suffix.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param materialized an instance of {@link Materialized} used to materialize a state store. Cannot be {@code null}.
* Note: the valueSerde will be automatically set to {@link org.apache.kafka.common.serialization.Serdes#Long() Serdes#Long()}
* if there is no valueSerde provided
* @return a windowed {@link KTable} that contains "update" records with unmodified keys and {@link Long} values
* that represent the latest (rolling) count (i.e., number of records) for each key per session
*/
KTable, Long> count(final Materialized> materialized);
/**
* Count the number of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code null} key or value are ignored.
*
* The result is written into a local {@link SessionStore} (which is basically an ever-updating materialized view)
* that can be queried using the name provided with {@link Materialized}.
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
*
* Not all updates might get sent downstream, as an internal cache will be used to deduplicate consecutive updates
* to the same window and key if caching is enabled on the {@link Materialized} instance.
* When caching is enabled 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 {@link StreamsConfig configuration}
* parameters for {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* To query the local {@link SessionStore} it must be obtained via
* {@link KafkaStreams#store(StoreQueryParameters) KafkaStreams#store(...)}:
*
{@code
* KafkaStreams streams = ... // compute sum
* Sting queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
* ReadOnlySessionStore localWindowStore = streams.store(queryableStoreName, QueryableStoreTypes.ReadOnlySessionStore);
* String key = "some-key";
* KeyValueIterator, Long> sumForKeyForWindows = 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 {@link 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.
* Therefore, the store name defined by the Materialized instance must be a valid Kafka topic name and cannot
* contain characters other than ASCII alphanumerics, '.', '_' and '-'.
* The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "storeName" is the provide store name defined
* in {@code Materialized}, and "-changelog" is a fixed suffix.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param named a {@link Named} config used to name the processor in the topology. Cannot be {@code null}.
* @param materialized an instance of {@link Materialized} used to materialize a state store. Cannot be {@code null}.
* Note: the valueSerde will be automatically set to {@link org.apache.kafka.common.serialization.Serdes#Long() Serdes#Long()}
* if there is no valueSerde provided
* @return a windowed {@link KTable} that contains "update" records with unmodified keys and {@link Long} values
* that represent the latest (rolling) count (i.e., number of records) for each key per session
*/
KTable, Long> count(final Named named,
final Materialized> materialized);
/**
* Aggregate the values of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code null} key or value are ignored.
* Aggregating is a generalization of {@link #reduce(Reducer) 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 {@link SessionStore} (which is basically an ever-updating materialized view).
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
*
* The specified {@link Initializer} is applied directly before the first input record per session is processed to
* provide an initial intermediate aggregation result that is used to process the first record per session.
* The specified {@link 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
* {@link Initializer}) and the record's value.
* The specified {@link Merger} is used to merge two existing sessions into one, i.e., when the windows overlap,
* they are merged into a single session and the old sessions are discarded.
* Thus, {@code aggregate()} can be used to compute aggregate functions like count (c.f. {@link #count()}).
*
* The default key and value serde from the config will be used for serializing the result.
* If a different serde is required then you should use
* {@link #aggregate(Initializer, Aggregator, Merger, Materialized)}.
*
* 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 {@link StreamsConfig configuration} parameters for
* {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* 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 "${applicationId}-${internalStoreName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "internalStoreName" is an internal name
* and "-changelog" is a fixed suffix.
* Note that the internal store name may not be queryable through Interactive Queries.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param initializer an {@link Initializer} that computes an initial intermediate aggregation result. Cannot be {@code null}.
* @param aggregator an {@link Aggregator} that computes a new aggregate result. Cannot be {@code null}.
* @param sessionMerger a {@link Merger} that combines two aggregation results. Cannot be {@code null}.
* @param the value type of the resulting {@link KTable}
* @return a windowed {@link KTable} that contains "update" records with unmodified keys, and values that represent
* the latest (rolling) aggregate for each key per session
*/
KTable, VR> aggregate(final Initializer initializer,
final Aggregator aggregator,
final Merger sessionMerger);
/**
* Aggregate the values of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code null} key or value are ignored.
* Aggregating is a generalization of {@link #reduce(Reducer) 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 {@link SessionStore} (which is basically an ever-updating materialized view).
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
*
* The specified {@link Initializer} is applied directly before the first input record per session is processed to
* provide an initial intermediate aggregation result that is used to process the first record per session.
* The specified {@link 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
* {@link Initializer}) and the record's value.
* The specified {@link Merger} is used to merge two existing sessions into one, i.e., when the windows overlap,
* they are merged into a single session and the old sessions are discarded.
* Thus, {@code aggregate()} can be used to compute aggregate functions like count (c.f. {@link #count()}).
*
* The default key and value serde from the config will be used for serializing the result.
* If a different serde is required then you should use
* {@link #aggregate(Initializer, Aggregator, Merger, Named, Materialized)}.
*
* 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 {@link StreamsConfig configuration}
* parameters for {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* 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 "${applicationId}-${internalStoreName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "internalStoreName" is an internal name
* and "-changelog" is a fixed suffix.
* Note that the internal store name may not be queryable through Interactive Queries.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param initializer an {@link Initializer} that computes an initial intermediate aggregation result. Cannot be {@code null}.
* @param aggregator an {@link Aggregator} that computes a new aggregate result. Cannot be {@code null}.
* @param sessionMerger a {@link Merger} that combines two aggregation results. Cannot be {@code null}.
* @param named a {@link Named} config used to name the processor in the topology. Cannot be {@code null}.
* @param the value type of the resulting {@link KTable}
* @return a windowed {@link KTable} that contains "update" records with unmodified keys, and values that represent
* the latest (rolling) aggregate for each key per session
*/
KTable, VR> aggregate(final Initializer initializer,
final Aggregator aggregator,
final Merger sessionMerger,
final Named named);
/**
* Aggregate the values of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code null} key or value are ignored.
* Aggregating is a generalization of {@link #reduce(Reducer) 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 {@link SessionStore} (which is basically an ever-updating materialized view)
* that can be queried using the store name as provided with {@link Materialized}.
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
*
* The specified {@link Initializer} is applied directly before the first input record per session is processed to
* provide an initial intermediate aggregation result that is used to process the first record per session.
* The specified {@link 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
* {@link Initializer}) and the record's value.
* The specified {@link Merger} is used to merge two existing sessions into one, i.e., when the windows overlap,
* they are merged into a single session and the old sessions are discarded.
* Thus, {@code aggregate()} can be used to compute aggregate functions like count (c.f. {@link #count()}).
*
* Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to
* the same window and key if caching is enabled on the {@link Materialized} instance.
* When caching is enabled 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 {@link StreamsConfig configuration} parameters for
* {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* To query the local {@link SessionStore} it must be obtained via
* {@link KafkaStreams#store(StoreQueryParameters) KafkaStreams#store(...)}:
*
{@code
* KafkaStreams streams = ... // some windowed aggregation on value type double
* Sting queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
* ReadOnlySessionStore sessionStore = streams.store(queryableStoreName, QueryableStoreTypes.sessionStore());
* String key = "some-key";
* KeyValueIterator, 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 {@link 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.
* Therefore, the store name defined by the {@link Materialized} instance must be a valid Kafka topic name and
* cannot contain characters other than ASCII alphanumerics, '.', '_' and '-'.
* The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "storeName" is the
* provide store name defined in {@link Materialized}, and "-changelog" is a fixed suffix.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param initializer an {@link Initializer} that computes an initial intermediate aggregation result. Cannot be {@code null}.
* @param aggregator an {@link Aggregator} that computes a new aggregate result. Cannot be {@code null}.
* @param sessionMerger a {@link Merger} that combines two aggregation results. Cannot be {@code null}.
* @param materialized a {@link Materialized} config used to materialize a state store. Cannot be {@code null}.
* @param the value type of the resulting {@link KTable}
* @return a windowed {@link KTable} that contains "update" records with unmodified keys, and values that represent
* the latest (rolling) aggregate for each key per session
*/
KTable, VR> aggregate(final Initializer initializer,
final Aggregator aggregator,
final Merger sessionMerger,
final Materialized> materialized);
/**
* Aggregate the values of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code null} key or value are ignored.
* Aggregating is a generalization of {@link #reduce(Reducer) 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 {@link SessionStore} (which is basically an ever-updating materialized view)
* that can be queried using the store name as provided with {@link Materialized}.
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
*
* The specified {@link Initializer} is applied directly before the first input record per session is processed to
* provide an initial intermediate aggregation result that is used to process the first record per session.
* The specified {@link 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
* {@link Initializer}) and the record's value.
* The specified {@link Merger} is used to merge two existing sessions into one, i.e., when the windows overlap,
* they are merged into a single session and the old sessions are discarded.
* Thus, {@code aggregate()} can be used to compute aggregate functions like count (c.f. {@link #count()}).
*
* Not all updates might get sent downstream, as an internal cache will be used to deduplicate consecutive updates
* to the same window and key if caching is enabled on the {@link Materialized} instance.
* When caching is enabled 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 {@link StreamsConfig configuration}
* parameters for {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* To query the local {@link SessionStore} it must be obtained via
* {@link KafkaStreams#store(StoreQueryParameters) KafkaStreams#store(...)}:
*
{@code
* KafkaStreams streams = ... // some windowed aggregation on value type double
* Sting queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
* ReadOnlySessionStore sessionStore = streams.store(queryableStoreName, QueryableStoreTypes.sessionStore());
* String key = "some-key";
* KeyValueIterator, 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 {@link 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.
* Therefore, the store name defined by the {@link Materialized} instance must be a valid Kafka topic name and
* cannot contain characters other than ASCII alphanumerics, '.', '_' and '-'.
* The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "storeName" is the
* provide store name defined in {@link Materialized}, and "-changelog" is a fixed suffix.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param initializer an {@link Initializer} that computes an initial intermediate aggregation result. Cannot be {@code null}.
* @param aggregator an {@link Aggregator} that computes a new aggregate result. Cannot be {@code null}.
* @param sessionMerger a {@link Merger} that combines two aggregation results. Cannot be {@code null}.
* @param named a {@link Named} config used to name the processor in the topology. Cannot be {@code null}.
* @param materialized a {@link Materialized} config used to materialize a state store. Cannot be {@code null}.
* @param the value type of the resulting {@link KTable}
* @return a windowed {@link KTable} that contains "update" records with unmodified keys, and values that represent
* the latest (rolling) aggregate for each key per session
*/
KTable, VR> aggregate(final Initializer initializer,
final Aggregator aggregator,
final Merger sessionMerger,
final Named named,
final Materialized> materialized);
/**
* Combine the values of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code 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. {@link #aggregate(Initializer, Aggregator, Merger)}).
* The result is written into a local {@link SessionStore} (which is basically an ever-updating materialized view).
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
* The default key and value serde from the config will be used for serializing the result.
* If a different serde is required then you should use {@link #reduce(Reducer, Materialized)} .
*
* The value of the first record per session initialized the session result.
* The specified {@link Reducer} is applied for each additional input record per session and computes a new
* aggregate using the current aggregate (first argument) and the record's value (second argument):
*
{@code
* // At the example of a Reducer
* new Reducer() {
* public Long apply(Long aggValue, Long currValue) {
* return aggValue + currValue;
* }
* }
* }
* Thus, {@code reduce()} 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 {@link StreamsConfig configuration} parameters for
* {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* 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 "${applicationId}-${internalStoreName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "internalStoreName" is an internal name
* and "-changelog" is a fixed suffix.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param reducer a {@link Reducer} that computes a new aggregate result. Cannot be {@code null}.
* @return a windowed {@link KTable} that contains "update" records with unmodified keys, and values that represent
* the latest (rolling) aggregate for each key per session
*/
KTable, V> reduce(final Reducer reducer);
/**
* Combine the values of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code 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. {@link #aggregate(Initializer, Aggregator, Merger)}).
* The result is written into a local {@link SessionStore} (which is basically an ever-updating materialized view).
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
* The default key and value serde from the config will be used for serializing the result.
* If a different serde is required then you should use {@link #reduce(Reducer, Named, Materialized)} .
*
* The value of the first record per session initialized the session result.
* The specified {@link Reducer} is applied for each additional input record per session and computes a new
* aggregate using the current aggregate (first argument) and the record's value (second argument):
*
{@code
* // At the example of a Reducer
* new Reducer() {
* public Long apply(Long aggValue, Long currValue) {
* return aggValue + currValue;
* }
* }
* }
* Thus, {@code reduce()} 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 {@link StreamsConfig configuration} parameters for
* {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* 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 "${applicationId}-${internalStoreName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "internalStoreName" is an internal name
* and "-changelog" is a fixed suffix.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param reducer a {@link Reducer} that computes a new aggregate result. Cannot be {@code null}.
* @param named a {@link Named} config used to name the processor in the topology. Cannot be {@code null}.
* @return a windowed {@link KTable} that contains "update" records with unmodified keys, and values that represent
* the latest (rolling) aggregate for each key per session
*/
KTable, V> reduce(final Reducer reducer, final Named named);
/**
* Combine the values of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code 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. {@link #aggregate(Initializer, Aggregator, Merger)}).
* The result is written into a local {@link SessionStore} (which is basically an ever-updating materialized view)
* that can be queried using the store name as provided with {@link Materialized}.
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
*
* The value of the first record per session initialized the session result.
* The specified {@link Reducer} is applied for each additional input record per session and computes a new
* aggregate using the current aggregate (first argument) and the record's value (second argument):
*
{@code
* // At the example of a Reducer
* new Reducer() {
* public Long apply(Long aggValue, Long currValue) {
* return aggValue + currValue;
* }
* }
* }
* Thus, {@code reduce()} can be used to compute aggregate functions like sum, min, or max.
*
* Not all updates might get sent downstream, as an internal cache will be used to deduplicate consecutive updates
* to the same window and key if caching is enabled on the {@link Materialized} instance.
* When caching is enabled 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 {@link StreamsConfig configuration}
* parameters for {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* To query the local {@link SessionStore} it must be obtained via
* {@link KafkaStreams#store(StoreQueryParameters) KafkaStreams#store(...)}:
*
{@code
* KafkaStreams streams = ... // compute sum
* Sting queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
* ReadOnlySessionStore localWindowStore = streams.store(queryableStoreName, QueryableStoreTypes.ReadOnlySessionStore);
* String key = "some-key";
* KeyValueIterator, Long> sumForKeyForWindows = 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 {@link 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.
* Therefore, the store name defined by the Materialized instance must be a valid Kafka topic name and cannot
* contain characters other than ASCII alphanumerics, '.', '_' and '-'.
* The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "storeName" is the provide store name defined
* in {@code Materialized}, and "-changelog" is a fixed suffix.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param reducer a {@link Reducer} that computes a new aggregate result. Cannot be {@code null}.
* @param materialized a {@link Materialized} config used to materialize a state store. Cannot be {@code null}.
* @return a windowed {@link KTable} that contains "update" records with unmodified keys, and values that represent
* the latest (rolling) aggregate for each key per session
*/
KTable, V> reduce(final Reducer reducer,
final Materialized> materialized);
/**
* Combine the values of records in this stream by the grouped key and defined sessions.
* Note that sessions are generated on a per-key basis and records with different keys create independent sessions.
* Records with {@code 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. {@link #aggregate(Initializer, Aggregator, Merger)}).
* The result is written into a local {@link SessionStore} (which is basically an ever-updating materialized view)
* that can be queried using the store name as provided with {@link Materialized}.
* Furthermore, updates to the store are sent downstream into a {@link KTable} changelog stream.
*
* The value of the first record per session initialized the session result.
* The specified {@link Reducer} is applied for each additional input record per session and computes a new
* aggregate using the current aggregate (first argument) and the record's value (second argument):
*
{@code
* // At the example of a Reducer
* new Reducer() {
* public Long apply(Long aggValue, Long currValue) {
* return aggValue + currValue;
* }
* }
* }
* Thus, {@code reduce()} can be used to compute aggregate functions like sum, min, or max.
*
* Not all updates might get sent downstream, as an internal cache will be used to deduplicate consecutive updates
* to the same window and key if caching is enabled on the {@link Materialized} instance.
* When caching is enabled 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 {@link StreamsConfig configuration}
* parameters for {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG cache size}, and
* {@link StreamsConfig#COMMIT_INTERVAL_MS_CONFIG commit interval}.
*
* To query the local {@link SessionStore} it must be obtained via
* {@link KafkaStreams#store(StoreQueryParameters)} KafkaStreams#store(...)}:
*
{@code
* KafkaStreams streams = ... // compute sum
* Sting queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
* ReadOnlySessionStore localWindowStore = streams.store(queryableStoreName, QueryableStoreTypes.ReadOnlySessionStore);
* String key = "some-key";
* KeyValueIterator, Long> sumForKeyForWindows = 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 {@link 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.
* Therefore, the store name defined by the Materialized instance must be a valid Kafka topic name and cannot
* contain characters other than ASCII alphanumerics, '.', '_' and '-'.
* The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is
* user-specified in {@link StreamsConfig} via parameter
* {@link StreamsConfig#APPLICATION_ID_CONFIG APPLICATION_ID_CONFIG}, "storeName" is the provide store name defined
* in {@link Materialized}, and "-changelog" is a fixed suffix.
*
* You can retrieve all generated internal topic names via {@link Topology#describe()}.
*
* @param reducer a {@link Reducer} that computes a new aggregate result. Cannot be {@code null}.
* @param named a {@link Named} config used to name the processor in the topology. Cannot be {@code null}.
* @param materialized a {@link Materialized} config used to materialize a state store. Cannot be {@code null}.
* @return a windowed {@link KTable} that contains "update" records with unmodified keys, and values that represent
* the latest (rolling) aggregate for each key per session
*/
KTable, V> reduce(final Reducer reducer,
final Named named,
final Materialized> materialized);
}