Class SessionWindowedKStreamImpl<K,​V>

    • Method Detail

      • count

        public KTable<Windowed<K>,​java.lang.Long> count()
        Description copied from interface: SessionWindowedKStream
        Count the number of records in this stream by the grouped key into SessionWindows. Records with null key or value are ignored.

        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.

        Specified by:
        count in interface SessionWindowedKStream<K,​V>
        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

        public KTable<Windowed<K>,​java.lang.Long> count​(Materialized<K,​java.lang.Long,​SessionStore<org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)
        Description copied from interface: SessionWindowedKStream
        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 name provided with Materialized.

        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 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 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
         Sting queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
         ReadOnlySessionStore<String,Long> localWindowStore = streams.store(queryableStoreName, QueryableStoreTypes.<String, Long>ReadOnlySessionStore<String, Long>);
         String key = "some-key";
         KeyValueIterator<Windowed<String>, 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 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 StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide store name defined in Materialized, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via Topology.describe().

        Specified by:
        count in interface SessionWindowedKStream<K,​V>
        Parameters:
        materialized - an instance of Materialized used to materialize a state store. Cannot be null. Note: the valueSerde will be automatically set to Serdes.Long() if there is no valueSerde provided
        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

        public KTable<Windowed<K>,​V> reduce​(Reducer<V> reducer)
        Description copied from interface: SessionWindowedKStream
        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. SessionWindowedKStream.aggregate(Initializer, Aggregator, Merger)). The result is written into a local SessionStore (which is basically an ever-updating materialized view).

        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) 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.

        Specified by:
        reduce in interface SessionWindowedKStream<K,​V>
        Parameters:
        reducer - a Reducer that computes a new aggregate result. Cannot be null.
        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

        public KTable<Windowed<K>,​V> reduce​(Reducer<V> reducer,
                                                  Materialized<K,​V,​SessionStore<org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)
        Description copied from interface: SessionWindowedKStream
        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. SessionWindowedKStream.aggregate(Initializer, Aggregator, Merger)). The result is written into a local SessionStore (which is basically an ever-updating materialized view) provided by the given Materialized instance.

        The specified Reducer is applied for each input record and computes a new aggregate using the current aggregate (first argument) and the record's value (second argument):

        
         // At the example of a Reducer<Long>
         new Reducer<Long>() {
           public Long apply(Long aggValue, Long currValue) {
             return aggValue + currValue;
           }
         }
         

        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, Materialized) 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 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 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
         Sting queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
         ReadOnlySessionStore<String,Long> localWindowStore = streams.store(queryableStoreName, QueryableStoreTypes.<String, Long>ReadOnlySessionStore<String, Long>);
         String key = "some-key";
         KeyValueIterator<Windowed<String>, 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 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 StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide store name defined in Materialized, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via Topology.describe().

        Specified by:
        reduce in interface SessionWindowedKStream<K,​V>
        Parameters:
        reducer - a Reducer that computes a new aggregate result. Cannot be null.
        materialized - an instance of Materialized used to materialize a state store. Cannot be null
        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

        public <T> KTable<Windowed<K>,​T> aggregate​(Initializer<T> initializer,
                                                         Aggregator<? super K,​? super V,​T> aggregator,
                                                         Merger<? super K,​T> sessionMerger)
        Description copied from interface: SessionWindowedKStream
        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 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. The specified Merger is used to merge 2 existing sessions into one, i.e., when the windows overlap, they are merged into a single session and the old sessions are discarded. Thus, aggregate(Initializer, Aggregator, Merger) can be used to compute aggregate functions like count (c.f. SessionWindowedKStream.count())

        The default value serde from config will be used for serializing the result. If a different serde is required then you should use SessionWindowedKStream.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 configuration parameters for cache size, and commit intervall.

        Specified by:
        aggregate in interface SessionWindowedKStream<K,​V>
        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
        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

        public <VR> KTable<Windowed<K>,​VR> aggregate​(Initializer<VR> initializer,
                                                           Aggregator<? super K,​? super V,​VR> aggregator,
                                                           Merger<? super K,​VR> sessionMerger,
                                                           Materialized<K,​VR,​SessionStore<org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)
        Description copied from interface: SessionWindowedKStream
        Aggregate the values of records in this stream by the grouped key and defined 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 name provided with Materialized. 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 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. * The specified Merger is used to merge 2 existing sessions into one, i.e., when the windows overlap, they are merged into a single session and the old sessions are discarded. Thus, aggregate(Initializer, Aggregator, Merger) can be used to compute aggregate functions like count (c.f. SessionWindowedKStream.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 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 configuration parameters for cache size, and commit intervall

        KafkaStreams#store(...).

        
         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<String, Long> sessionStore = streams.store(queryableStoreName, 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 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 StreamsConfig via parameter APPLICATION_ID_CONFIG, "storeName" is the provide store name defined in Materialized, and "-changelog" is a fixed suffix. You can retrieve all generated internal topic names via Topology.describe().

        Specified by:
        aggregate in interface SessionWindowedKStream<K,​V>
        Type Parameters:
        VR - the value type of the resulting KTable
        Parameters:
        initializer - the instance of Initializer
        aggregator - the instance of Aggregator
        sessionMerger - the instance of Merger
        materialized - an instance of Materialized used to materialize a state store. Cannot be null
        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