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| <div class="sub-title"><span class="package-label-in-type">Package</span> <a href="package-summary.html">org.apache.kafka.streams.kstream</a></div> |
| <h1 title="Interface SessionWindowedKStream" class="title">Interface SessionWindowedKStream<K,​V></h1> |
| </div> |
| <section class="description"> |
| <dl class="notes"> |
| <dt>Type Parameters:</dt> |
| <dd><code>K</code> - Type of keys</dd> |
| <dd><code>V</code> - Type of values</dd> |
| </dl> |
| <hr> |
| <pre>public interface <span class="type-name-label">SessionWindowedKStream<K,​V></span></pre> |
| <div class="block"><code>SessionWindowedKStream</code> is an abstraction of a <i>windowed</i> record stream of <a href="../KeyValue.html" title="class in org.apache.kafka.streams"><code>KeyValue</code></a> pairs. |
| It is an intermediate representation after a grouping and windowing of a <a href="KStream.html" title="interface in org.apache.kafka.streams.kstream"><code>KStream</code></a> before an aggregation is |
| applied to the new (partitioned) windows resulting in a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> (a <emph>windowed</emph> |
| <code>KTable</code> is a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> with key type <a href="Windowed.html" title="class in org.apache.kafka.streams.kstream"><code>Windowed<K></code></a>). |
| <p> |
| <a href="SessionWindows.html" title="class in org.apache.kafka.streams.kstream"><code>SessionWindows</code></a> are dynamic data driven windows. |
| They have no fixed time boundaries, rather the size of the window is determined by the records. |
| <p> |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating |
| materialized view) that can be queried using the name provided in the <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> instance. |
| Furthermore, updates to the store are sent downstream into a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> changelog stream, where |
| "windowed" implies that the <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> 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 <a href="SessionWindows.html#grace(java.time.Duration)"><code>SessionWindows.grace(Duration)</code></a>). |
| <p> |
| A <code>SessionWindowedKStream</code> must be obtained from a <a href="KGroupedStream.html" title="interface in org.apache.kafka.streams.kstream"><code>KGroupedStream</code></a> via |
| <a href="KGroupedStream.html#windowedBy(org.apache.kafka.streams.kstream.SessionWindows)"><code>KGroupedStream.windowedBy(SessionWindows)</code></a>.</div> |
| <dl class="notes"> |
| <dt>See Also:</dt> |
| <dd><a href="KStream.html" title="interface in org.apache.kafka.streams.kstream"><code>KStream</code></a>, |
| <a href="KGroupedStream.html" title="interface in org.apache.kafka.streams.kstream"><code>KGroupedStream</code></a>, |
| <a href="SessionWindows.html" title="class in org.apache.kafka.streams.kstream"><code>SessionWindows</code></a></dd> |
| </dl> |
| </section> |
| <section class="summary"> |
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| <h2>Method Summary</h2> |
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| <tr> |
| <th class="col-first" scope="col">Modifier and Type</th> |
| <th class="col-second" scope="col">Method</th> |
| <th class="col-last" scope="col">Description</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr class="alt-color" id="i0"> |
| <td class="col-first"><code><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​VR></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger)">aggregate</a></span>​(<a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream">Initializer</a><VR> initializer, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​VR> aggregator, |
| <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream">Merger</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR> sessionMerger)</code></th> |
| <td class="col-last"> |
| <div class="block">Aggregate the values of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="row-color" id="i1"> |
| <td class="col-first"><code><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​VR></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger,org.apache.kafka.streams.kstream.Materialized)">aggregate</a></span>​(<a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream">Initializer</a><VR> initializer, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​VR> aggregator, |
| <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream">Merger</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR> sessionMerger, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="col-last"> |
| <div class="block">Aggregate the values of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="alt-color" id="i2"> |
| <td class="col-first"><code><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​VR></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger,org.apache.kafka.streams.kstream.Named)">aggregate</a></span>​(<a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream">Initializer</a><VR> initializer, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​VR> aggregator, |
| <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream">Merger</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR> sessionMerger, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named)</code></th> |
| <td class="col-last"> |
| <div class="block">Aggregate the values of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="row-color" id="i3"> |
| <td class="col-first"><code><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​VR></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger,org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)">aggregate</a></span>​(<a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream">Initializer</a><VR> initializer, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​VR> aggregator, |
| <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream">Merger</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR> sessionMerger, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="col-last"> |
| <div class="block">Aggregate the values of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="alt-color" id="i4"> |
| <td class="col-first"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#count()">count</a></span>()</code></th> |
| <td class="col-last"> |
| <div class="block">Count the number of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="row-color" id="i5"> |
| <td class="col-first"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#count(org.apache.kafka.streams.kstream.Materialized)">count</a></span>​(<a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="col-last"> |
| <div class="block">Count the number of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="alt-color" id="i6"> |
| <td class="col-first"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#count(org.apache.kafka.streams.kstream.Named)">count</a></span>​(<a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named)</code></th> |
| <td class="col-last"> |
| <div class="block">Count the number of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="row-color" id="i7"> |
| <td class="col-first"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#count(org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)">count</a></span>​(<a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="col-last"> |
| <div class="block">Count the number of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="alt-color" id="i8"> |
| <td class="col-first"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#reduce(org.apache.kafka.streams.kstream.Reducer)">reduce</a></span>​(<a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>> reducer)</code></th> |
| <td class="col-last"> |
| <div class="block">Combine the values of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="row-color" id="i9"> |
| <td class="col-first"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Materialized)">reduce</a></span>​(<a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>> reducer, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="col-last"> |
| <div class="block">Combine the values of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="alt-color" id="i10"> |
| <td class="col-first"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Named)">reduce</a></span>​(<a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>> reducer, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named)</code></th> |
| <td class="col-last"> |
| <div class="block">Combine the values of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| <tr class="row-color" id="i11"> |
| <td class="col-first"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)">reduce</a></span>​(<a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>> reducer, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="col-last"> |
| <div class="block">Combine the values of records in this stream by the grouped key and defined sessions.</div> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </div> |
| </section> |
| </li> |
| </ul> |
| </section> |
| <section class="details"> |
| <ul class="details-list"> |
| <!-- ============ METHOD DETAIL ========== --> |
| <li> |
| <section class="method-details" id="method.detail"> |
| <h2>Method Details</h2> |
| <ul class="member-list"> |
| <li> |
| <section class="detail" id="count()"> |
| <h3>count</h3> |
| <div class="member-signature"><span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>></span> <span class="member-name">count</span>()</div> |
| <div class="block">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</code> key or value are ignored. |
| <p> |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (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 <a href="#count(org.apache.kafka.streams.kstream.Materialized)"><code>count(Materialized)</code></a>. |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> parameters for |
| <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "internalStoreName" is an internal name |
| and "-changelog" is a fixed suffix. |
| Note that the internal store name may not be queryable through Interactive Queries. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys and <a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link"><code>Long</code></a> values |
| that represent the latest (rolling) count (i.e., number of records) for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="count(org.apache.kafka.streams.kstream.Named)"> |
| <h3>count</h3> |
| <div class="member-signature"><span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>></span> <span class="member-name">count</span>​(<span class="parameters"><a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named)</span></div> |
| <div class="block">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</code> key or value are ignored. |
| <p> |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (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 <a href="#count(org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)"><code>count(Named, Materialized)</code></a>. |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> parameters for |
| <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "internalStoreName" is an internal name |
| and "-changelog" is a fixed suffix. |
| Note that the internal store name may not be queryable through Interactive Queries. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>named</code> - a <a href="Named.html" title="class in org.apache.kafka.streams.kstream"><code>Named</code></a> config used to name the processor in the topology. Cannot be <code>null</code>.</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys and <a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link"><code>Long</code></a> values |
| that represent the latest (rolling) count (i.e., number of records) for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="count(org.apache.kafka.streams.kstream.Materialized)"> |
| <h3>count</h3> |
| <div class="member-signature"><span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>></span> <span class="member-name">count</span>​(<span class="parameters"><a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</span></div> |
| <div class="block">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</code> key or value are ignored. |
| <p> |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the name provided with <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a>. |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> changelog stream. |
| <p> |
| 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 <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> |
| parameters for <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| To query the local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> it must be obtained via |
| <a href="../KafkaStreams.html#store(org.apache.kafka.streams.StoreQueryParameters)"><code>KafkaStreams#store(...)</code></a>: |
| <pre><code> |
| 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) |
| </code></pre> |
| For non-local keys, a custom RPC mechanism must be implemented using <a href="../KafkaStreams.html#metadataForAllStreamsClients()"><code>KafkaStreams.metadataForAllStreamsClients()</code></a> to |
| query the value of the key on a parallel running instance of your Kafka Streams application. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "storeName" is the provide store name defined |
| in <code>Materialized</code>, and "-changelog" is a fixed suffix. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>materialized</code> - an instance of <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> used to materialize a state store. Cannot be <code>null</code>. |
| Note: the valueSerde will be automatically set to <a href="../../common/serialization/Serdes.html#Long()"><code>Serdes#Long()</code></a> |
| if there is no valueSerde provided</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys and <a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link"><code>Long</code></a> values |
| that represent the latest (rolling) count (i.e., number of records) for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="count(org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)"> |
| <h3>count</h3> |
| <div class="member-signature"><span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>></span> <span class="member-name">count</span>​(<span class="parameters"><a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​<a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link">Long</a>,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</span></div> |
| <div class="block">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</code> key or value are ignored. |
| <p> |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the name provided with <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a>. |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> changelog stream. |
| <p> |
| 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 <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> |
| parameters for <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| To query the local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> it must be obtained via |
| <a href="../KafkaStreams.html#store(org.apache.kafka.streams.StoreQueryParameters)"><code>KafkaStreams#store(...)</code></a>: |
| <pre><code> |
| 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) |
| </code></pre> |
| For non-local keys, a custom RPC mechanism must be implemented using <a href="../KafkaStreams.html#metadataForAllStreamsClients()"><code>KafkaStreams.metadataForAllStreamsClients()</code></a> to |
| query the value of the key on a parallel running instance of your Kafka Streams application. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "storeName" is the provide store name defined |
| in <code>Materialized</code>, and "-changelog" is a fixed suffix. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>named</code> - a <a href="Named.html" title="class in org.apache.kafka.streams.kstream"><code>Named</code></a> config used to name the processor in the topology. Cannot be <code>null</code>.</dd> |
| <dd><code>materialized</code> - an instance of <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> used to materialize a state store. Cannot be <code>null</code>. |
| Note: the valueSerde will be automatically set to <a href="../../common/serialization/Serdes.html#Long()"><code>Serdes#Long()</code></a> |
| if there is no valueSerde provided</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys and <a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link"><code>Long</code></a> values |
| that represent the latest (rolling) count (i.e., number of records) for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger)"> |
| <h3>aggregate</h3> |
| <div class="member-signature"><span class="type-parameters"><VR></span> <span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​VR></span> <span class="member-name">aggregate</span>​(<span class="parameters"><a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream">Initializer</a><VR> initializer, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​VR> aggregator, |
| <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream">Merger</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR> sessionMerger)</span></div> |
| <div class="block">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</code> key or value are ignored. |
| Aggregating is a generalization of <a href="#reduce(org.apache.kafka.streams.kstream.Reducer)"><code>combining via reduce(...)</code></a> as it, for example, |
| allows the result to have a different type than the input values. |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view). |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> changelog stream. |
| <p> |
| The specified <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> 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 <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> 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 |
| <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a>) and the record's value. |
| The specified <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream"><code>Merger</code></a> 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()</code> can be used to compute aggregate functions like count (c.f. <a href="#count()"><code>count()</code></a>). |
| <p> |
| 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 |
| <a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger,org.apache.kafka.streams.kstream.Materialized)"><code>aggregate(Initializer, Aggregator, Merger, Materialized)</code></a>. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> parameters for |
| <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "internalStoreName" is an internal name |
| and "-changelog" is a fixed suffix. |
| Note that the internal store name may not be queryable through Interactive Queries. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Type Parameters:</dt> |
| <dd><code>VR</code> - the value type of the resulting <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a></dd> |
| <dt>Parameters:</dt> |
| <dd><code>initializer</code> - an <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> that computes an initial intermediate aggregation result. Cannot be <code>null</code>.</dd> |
| <dd><code>aggregator</code> - an <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that computes a new aggregate result. Cannot be <code>null</code>.</dd> |
| <dd><code>sessionMerger</code> - a <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream"><code>Merger</code></a> that combines two aggregation results. Cannot be <code>null</code>.</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys, and values that represent |
| the latest (rolling) aggregate for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger,org.apache.kafka.streams.kstream.Named)"> |
| <h3>aggregate</h3> |
| <div class="member-signature"><span class="type-parameters"><VR></span> <span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​VR></span> <span class="member-name">aggregate</span>​(<span class="parameters"><a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream">Initializer</a><VR> initializer, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​VR> aggregator, |
| <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream">Merger</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR> sessionMerger, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named)</span></div> |
| <div class="block">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</code> key or value are ignored. |
| Aggregating is a generalization of <a href="#reduce(org.apache.kafka.streams.kstream.Reducer)"><code>combining via reduce(...)</code></a> as it, for example, |
| allows the result to have a different type than the input values. |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view). |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> changelog stream. |
| <p> |
| The specified <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> 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 <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> 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 |
| <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a>) and the record's value. |
| The specified <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream"><code>Merger</code></a> 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()</code> can be used to compute aggregate functions like count (c.f. <a href="#count()"><code>count()</code></a>). |
| <p> |
| 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 |
| <a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger,org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)"><code>aggregate(Initializer, Aggregator, Merger, Named, Materialized)</code></a>. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> |
| parameters for <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "internalStoreName" is an internal name |
| and "-changelog" is a fixed suffix. |
| Note that the internal store name may not be queryable through Interactive Queries. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Type Parameters:</dt> |
| <dd><code>VR</code> - the value type of the resulting <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a></dd> |
| <dt>Parameters:</dt> |
| <dd><code>initializer</code> - an <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> that computes an initial intermediate aggregation result. Cannot be <code>null</code>.</dd> |
| <dd><code>aggregator</code> - an <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that computes a new aggregate result. Cannot be <code>null</code>.</dd> |
| <dd><code>sessionMerger</code> - a <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream"><code>Merger</code></a> that combines two aggregation results. Cannot be <code>null</code>.</dd> |
| <dd><code>named</code> - a <a href="Named.html" title="class in org.apache.kafka.streams.kstream"><code>Named</code></a> config used to name the processor in the topology. Cannot be <code>null</code>.</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys, and values that represent |
| the latest (rolling) aggregate for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger,org.apache.kafka.streams.kstream.Materialized)"> |
| <h3>aggregate</h3> |
| <div class="member-signature"><span class="type-parameters"><VR></span> <span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​VR></span> <span class="member-name">aggregate</span>​(<span class="parameters"><a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream">Initializer</a><VR> initializer, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​VR> aggregator, |
| <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream">Merger</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR> sessionMerger, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</span></div> |
| <div class="block">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</code> key or value are ignored. |
| Aggregating is a generalization of <a href="#reduce(org.apache.kafka.streams.kstream.Reducer)"><code>combining via reduce(...)</code></a> as it, for example, |
| allows the result to have a different type than the input values. |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the store name as provided with <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a>. |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> changelog stream. |
| <p> |
| The specified <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> 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 <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> 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 |
| <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a>) and the record's value. |
| The specified <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream"><code>Merger</code></a> 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()</code> can be used to compute aggregate functions like count (c.f. <a href="#count()"><code>count()</code></a>). |
| <p> |
| 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 <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> parameters for |
| <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| To query the local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> it must be obtained via |
| <a href="../KafkaStreams.html#store(org.apache.kafka.streams.StoreQueryParameters)"><code>KafkaStreams#store(...)</code></a>: |
| <pre><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<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) |
| </code></pre> |
| For non-local keys, a custom RPC mechanism must be implemented using <a href="../KafkaStreams.html#metadataForAllStreamsClients()"><code>KafkaStreams.metadataForAllStreamsClients()</code></a> to |
| query the value of the key on a parallel running instance of your Kafka Streams application. |
| <p> |
| 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 <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "storeName" is the |
| provide store name defined in <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a>, and "-changelog" is a fixed suffix. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Type Parameters:</dt> |
| <dd><code>VR</code> - the value type of the resulting <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a></dd> |
| <dt>Parameters:</dt> |
| <dd><code>initializer</code> - an <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> that computes an initial intermediate aggregation result. Cannot be <code>null</code>.</dd> |
| <dd><code>aggregator</code> - an <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that computes a new aggregate result. Cannot be <code>null</code>.</dd> |
| <dd><code>sessionMerger</code> - a <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream"><code>Merger</code></a> that combines two aggregation results. Cannot be <code>null</code>.</dd> |
| <dd><code>materialized</code> - a <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> config used to materialize a state store. Cannot be <code>null</code>.</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys, and values that represent |
| the latest (rolling) aggregate for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger,org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)"> |
| <h3>aggregate</h3> |
| <div class="member-signature"><span class="type-parameters"><VR></span> <span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​VR></span> <span class="member-name">aggregate</span>​(<span class="parameters"><a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream">Initializer</a><VR> initializer, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​VR> aggregator, |
| <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream">Merger</a><? super <a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR> sessionMerger, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​VR,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</span></div> |
| <div class="block">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</code> key or value are ignored. |
| Aggregating is a generalization of <a href="#reduce(org.apache.kafka.streams.kstream.Reducer)"><code>combining via reduce(...)</code></a> as it, for example, |
| allows the result to have a different type than the input values. |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the store name as provided with <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a>. |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> changelog stream. |
| <p> |
| The specified <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> 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 <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> 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 |
| <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a>) and the record's value. |
| The specified <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream"><code>Merger</code></a> 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()</code> can be used to compute aggregate functions like count (c.f. <a href="#count()"><code>count()</code></a>). |
| <p> |
| 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 <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> |
| parameters for <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| To query the local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> it must be obtained via |
| <a href="../KafkaStreams.html#store(org.apache.kafka.streams.StoreQueryParameters)"><code>KafkaStreams#store(...)</code></a>: |
| <pre><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<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) |
| </code></pre> |
| For non-local keys, a custom RPC mechanism must be implemented using <a href="../KafkaStreams.html#metadataForAllStreamsClients()"><code>KafkaStreams.metadataForAllStreamsClients()</code></a> to |
| query the value of the key on a parallel running instance of your Kafka Streams application. |
| <p> |
| 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 <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "storeName" is the |
| provide store name defined in <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a>, and "-changelog" is a fixed suffix. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Type Parameters:</dt> |
| <dd><code>VR</code> - the value type of the resulting <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a></dd> |
| <dt>Parameters:</dt> |
| <dd><code>initializer</code> - an <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> that computes an initial intermediate aggregation result. Cannot be <code>null</code>.</dd> |
| <dd><code>aggregator</code> - an <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that computes a new aggregate result. Cannot be <code>null</code>.</dd> |
| <dd><code>sessionMerger</code> - a <a href="Merger.html" title="interface in org.apache.kafka.streams.kstream"><code>Merger</code></a> that combines two aggregation results. Cannot be <code>null</code>.</dd> |
| <dd><code>named</code> - a <a href="Named.html" title="class in org.apache.kafka.streams.kstream"><code>Named</code></a> config used to name the processor in the topology. Cannot be <code>null</code>.</dd> |
| <dd><code>materialized</code> - a <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> config used to materialize a state store. Cannot be <code>null</code>.</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys, and values that represent |
| the latest (rolling) aggregate for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="reduce(org.apache.kafka.streams.kstream.Reducer)"> |
| <h3>reduce</h3> |
| <div class="member-signature"><span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>></span> <span class="member-name">reduce</span>​(<span class="parameters"><a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>> reducer)</span></div> |
| <div class="block">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</code> 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. <a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger)"><code>aggregate(Initializer, Aggregator, Merger)</code></a>). |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view). |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> 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 <a href="#reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Materialized)"><code>reduce(Reducer, Materialized)</code></a> . |
| <p> |
| The value of the first record per session initialized the session result. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> 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): |
| <pre><code> |
| // At the example of a Reducer<Long> |
| new Reducer<Long>() { |
| public Long apply(Long aggValue, Long currValue) { |
| return aggValue + currValue; |
| } |
| } |
| </code></pre> |
| Thus, <code>reduce()</code> can be used to compute aggregate functions like sum, min, or max. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> parameters for |
| <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "internalStoreName" is an internal name |
| and "-changelog" is a fixed suffix. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>reducer</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that computes a new aggregate result. Cannot be <code>null</code>.</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys, and values that represent |
| the latest (rolling) aggregate for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Named)"> |
| <h3>reduce</h3> |
| <div class="member-signature"><span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>></span> <span class="member-name">reduce</span>​(<span class="parameters"><a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>> reducer, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named)</span></div> |
| <div class="block">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</code> 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. <a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger)"><code>aggregate(Initializer, Aggregator, Merger)</code></a>). |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view). |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> 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 <a href="#reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)"><code>reduce(Reducer, Named, Materialized)</code></a> . |
| <p> |
| The value of the first record per session initialized the session result. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> 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): |
| <pre><code> |
| // At the example of a Reducer<Long> |
| new Reducer<Long>() { |
| public Long apply(Long aggValue, Long currValue) { |
| return aggValue + currValue; |
| } |
| } |
| </code></pre> |
| Thus, <code>reduce()</code> can be used to compute aggregate functions like sum, min, or max. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> parameters for |
| <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "internalStoreName" is an internal name |
| and "-changelog" is a fixed suffix. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>reducer</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that computes a new aggregate result. Cannot be <code>null</code>.</dd> |
| <dd><code>named</code> - a <a href="Named.html" title="class in org.apache.kafka.streams.kstream"><code>Named</code></a> config used to name the processor in the topology. Cannot be <code>null</code>.</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys, and values that represent |
| the latest (rolling) aggregate for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Materialized)"> |
| <h3>reduce</h3> |
| <div class="member-signature"><span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>></span> <span class="member-name">reduce</span>​(<span class="parameters"><a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>> reducer, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</span></div> |
| <div class="block">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</code> 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. <a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger)"><code>aggregate(Initializer, Aggregator, Merger)</code></a>). |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the store name as provided with <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a>. |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> changelog stream. |
| <p> |
| The value of the first record per session initialized the session result. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> 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): |
| <pre><code> |
| // At the example of a Reducer<Long> |
| new Reducer<Long>() { |
| public Long apply(Long aggValue, Long currValue) { |
| return aggValue + currValue; |
| } |
| } |
| </code></pre> |
| Thus, <code>reduce()</code> can be used to compute aggregate functions like sum, min, or max. |
| <p> |
| 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 <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> |
| parameters for <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| To query the local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> it must be obtained via |
| <a href="../KafkaStreams.html#store(org.apache.kafka.streams.StoreQueryParameters)"><code>KafkaStreams#store(...)</code></a>: |
| <pre><code> |
| 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) |
| </code></pre> |
| For non-local keys, a custom RPC mechanism must be implemented using <a href="../KafkaStreams.html#metadataForAllStreamsClients()"><code>KafkaStreams.metadataForAllStreamsClients()</code></a> to |
| query the value of the key on a parallel running instance of your Kafka Streams application. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "storeName" is the provide store name defined |
| in <code>Materialized</code>, and "-changelog" is a fixed suffix. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>reducer</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that computes a new aggregate result. Cannot be <code>null</code>.</dd> |
| <dd><code>materialized</code> - a <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> config used to materialize a state store. Cannot be <code>null</code>.</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys, and values that represent |
| the latest (rolling) aggregate for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)"> |
| <h3>reduce</h3> |
| <div class="member-signature"><span class="return-type"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="Windowed.html" title="class in org.apache.kafka.streams.kstream">Windowed</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>></span> <span class="member-name">reduce</span>​(<span class="parameters"><a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>> reducer, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">K</a>,​<a href="SessionWindowedKStream.html" title="type parameter in SessionWindowedKStream">V</a>,​<a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state">SessionStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</span></div> |
| <div class="block">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</code> 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. <a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Merger)"><code>aggregate(Initializer, Aggregator, Merger)</code></a>). |
| The result is written into a local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the store name as provided with <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a>. |
| Furthermore, updates to the store are sent downstream into a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> changelog stream. |
| <p> |
| The value of the first record per session initialized the session result. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> 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): |
| <pre><code> |
| // At the example of a Reducer<Long> |
| new Reducer<Long>() { |
| public Long apply(Long aggValue, Long currValue) { |
| return aggValue + currValue; |
| } |
| } |
| </code></pre> |
| Thus, <code>reduce()</code> can be used to compute aggregate functions like sum, min, or max. |
| <p> |
| 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 <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>configuration</code></a> |
| parameters for <a href="../StreamsConfig.html#CACHE_MAX_BYTES_BUFFERING_CONFIG"><code>cache size</code></a>, and |
| <a href="../StreamsConfig.html#COMMIT_INTERVAL_MS_CONFIG"><code>commit interval</code></a>. |
| <p> |
| To query the local <a href="../state/SessionStore.html" title="interface in org.apache.kafka.streams.state"><code>SessionStore</code></a> it must be obtained via |
| <a href="../KafkaStreams.html#store(org.apache.kafka.streams.StoreQueryParameters)"><code>KafkaStreams.store(StoreQueryParameters)</code></a> KafkaStreams#store(...)}: |
| <pre><code> |
| 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) |
| </code></pre> |
| For non-local keys, a custom RPC mechanism must be implemented using <a href="../KafkaStreams.html#metadataForAllStreamsClients()"><code>KafkaStreams.metadataForAllStreamsClients()</code></a> to |
| query the value of the key on a parallel running instance of your Kafka Streams application. |
| <p> |
| 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 <a href="../StreamsConfig.html" title="class in org.apache.kafka.streams"><code>StreamsConfig</code></a> via parameter |
| <a href="../StreamsConfig.html#APPLICATION_ID_CONFIG"><code>APPLICATION_ID_CONFIG</code></a>, "storeName" is the provide store name defined |
| in <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a>, and "-changelog" is a fixed suffix. |
| <p> |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>reducer</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that computes a new aggregate result. Cannot be <code>null</code>.</dd> |
| <dd><code>named</code> - a <a href="Named.html" title="class in org.apache.kafka.streams.kstream"><code>Named</code></a> config used to name the processor in the topology. Cannot be <code>null</code>.</dd> |
| <dd><code>materialized</code> - a <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> config used to materialize a state store. Cannot be <code>null</code>.</dd> |
| <dt>Returns:</dt> |
| <dd>a windowed <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that contains "update" records with unmodified keys, and values that represent |
| the latest (rolling) aggregate for each key per session</dd> |
| </dl> |
| </section> |
| </li> |
| </ul> |
| </section> |
| </li> |
| </ul> |
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