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| <div class="subTitle"><span class="packageLabelInType">Package</span> <a href="package-summary.html">org.apache.kafka.streams.kstream</a></div> |
| <h2 title="Interface KGroupedTable" class="title">Interface KGroupedTable<K,​V></h2> |
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| <dl> |
| <dt><span class="paramLabel">Type Parameters:</span></dt> |
| <dd><code>K</code> - Type of keys</dd> |
| <dd><code>V</code> - Type of values</dd> |
| </dl> |
| <hr> |
| <pre>public interface <span class="typeNameLabel">KGroupedTable<K,​V></span></pre> |
| <div class="block"><code>KGroupedTable</code> is an abstraction of a <i>re-grouped changelog stream</i> from a primary-keyed table, |
| usually on a different grouping key than the original primary key. |
| <p> |
| It is an intermediate representation after a re-grouping of a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> before an aggregation is applied to the |
| new partitions resulting in a new <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| <p> |
| A <code>KGroupedTable</code> must be obtained from a <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> via <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>groupBy(...)</code></a>.</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a></dd> |
| </dl> |
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| <h3>Method Summary</h3> |
| <table class="memberSummary"> |
| <caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd"> </span></span><span id="t2" class="tableTab"><span><a href="javascript:show(2);">Instance Methods</a></span><span class="tabEnd"> </span></span><span id="t3" class="tableTab"><span><a href="javascript:show(4);">Abstract Methods</a></span><span class="tabEnd"> </span></span></caption> |
| <tr> |
| <th class="colFirst" scope="col">Modifier and Type</th> |
| <th class="colSecond" scope="col">Method</th> |
| <th class="colLast" scope="col">Description</th> |
| </tr> |
| <tr id="i0" class="altColor"> |
| <td class="colFirst"><code><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator)">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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> adder, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> subtractor)</code></th> |
| <td class="colLast"> |
| <div class="block">Aggregate the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> using default serializers and deserializers.</div> |
| </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator,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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> adder, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> subtractor, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="colLast"> |
| <div class="block">Aggregate the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i2" class="altColor"> |
| <td class="colFirst"><code><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator,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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> adder, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> subtractor, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named)</code></th> |
| <td class="colLast"> |
| <div class="block">Aggregate the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> using default serializers and deserializers.</div> |
| </td> |
| </tr> |
| <tr id="i3" class="rowColor"> |
| <td class="colFirst"><code><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator,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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> adder, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> subtractor, |
| <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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="colLast"> |
| <div class="block">Aggregate the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i4" class="altColor"> |
| <td class="colFirst"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#count()">count</a></span>()</code></th> |
| <td class="colLast"> |
| <div class="block">Count number of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to |
| the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i5" class="rowColor"> |
| <td class="colFirst"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="colLast"> |
| <div class="block">Count number of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to |
| the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i6" class="altColor"> |
| <td class="colFirst"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><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="colLast"> |
| <div class="block">Count number of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to |
| the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i7" class="rowColor"> |
| <td class="colFirst"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="colLast"> |
| <div class="block">Count number of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to |
| the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i8" class="altColor"> |
| <td class="colFirst"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#reduce(org.apache.kafka.streams.kstream.Reducer,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="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> adder, |
| <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> subtractor)</code></th> |
| <td class="colLast"> |
| <div class="block">Combine the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i9" class="rowColor"> |
| <td class="colFirst"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#reduce(org.apache.kafka.streams.kstream.Reducer,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="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> adder, |
| <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> subtractor, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="colLast"> |
| <div class="block">Combine the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i10" class="altColor"> |
| <td class="colFirst"><code><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#reduce(org.apache.kafka.streams.kstream.Reducer,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="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> adder, |
| <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> subtractor, |
| <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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</code></th> |
| <td class="colLast"> |
| <div class="block">Combine the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>.</div> |
| </td> |
| </tr> |
| </table> |
| </li> |
| </ul> |
| </section> |
| </li> |
| </ul> |
| </div> |
| <div class="details"> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <!-- ============ METHOD DETAIL ========== --> |
| <section role="region"> |
| <ul class="blockList"> |
| <li class="blockList"><a id="method.detail"> |
| <!-- --> |
| </a> |
| <h3>Method Detail</h3> |
| <a id="count(org.apache.kafka.streams.kstream.Materialized)"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>count</h4> |
| <pre class="methodSignature"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>> count​(<a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</pre> |
| <div class="block">Count number of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to |
| the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| Records with <code>null</code> key are ignored. |
| The result is written into a local <a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the provided <code>queryableStoreName</code>. |
| 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 is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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/ReadOnlyKeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>ReadOnlyKeyValueStore</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 = ... // counting words |
| ReadOnlyKeyValueStore<K, ValueAndTimestamp<Long>> localStore = streams.store(queryableStoreName, QueryableStoreTypes.<K, ValueAndTimestamp<Long>> timestampedKeyValueStore()); |
| K key = "some-word"; |
| ValueAndTimestamp<Long> countForWord = localStore.get(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#allMetadata()"><code>KafkaStreams.allMetadata()</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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>materialized</code> - the instance of <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> used to materialize the state store. Cannot be <code>null</code></dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink"><code>Long</code></a> values that |
| represent the latest (rolling) count (i.e., number of records) for each key</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="count(org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>count</h4> |
| <pre class="methodSignature"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>> count​(<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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</pre> |
| <div class="block">Count number of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to |
| the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| Records with <code>null</code> key are ignored. |
| The result is written into a local <a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the provided <code>queryableStoreName</code>. |
| 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 is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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/ReadOnlyKeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>ReadOnlyKeyValueStore</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 = ... // counting words |
| ReadOnlyKeyValueStore<K, ValueAndTimestamp<Long>> localStore = streams.store(queryableStoreName, QueryableStoreTypes.<K, ValueAndTimestamp<Long>> timestampedKeyValueStore()); |
| K key = "some-word"; |
| ValueAndTimestamp<Long> countForWord = localStore.get(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#allMetadata()"><code>KafkaStreams.allMetadata()</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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>named</code> - the <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</dd> |
| <dd><code>materialized</code> - the instance of <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> used to materialize the state store. Cannot be <code>null</code></dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink"><code>Long</code></a> values that |
| represent the latest (rolling) count (i.e., number of records) for each key</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="count()"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>count</h4> |
| <pre class="methodSignature"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>> count()</pre> |
| <div class="block">Count number of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to |
| the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| Records with <code>null</code> key are ignored. |
| The result is written into a local <a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</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> |
| Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink"><code>Long</code></a> values that |
| represent the latest (rolling) count (i.e., number of records) for each key</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="count(org.apache.kafka.streams.kstream.Named)"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>count</h4> |
| <pre class="methodSignature"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink">Long</a>> count​(<a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named)</pre> |
| <div class="block">Count number of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to |
| the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| Records with <code>null</code> key are ignored. |
| The result is written into a local <a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</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> |
| Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>named</code> - the <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</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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/11/docs/api/java.base/java/lang/Long.html?is-external=true" title="class or interface in java.lang" class="externalLink"><code>Long</code></a> values that |
| represent the latest (rolling) count (i.e., number of records) for each key</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Materialized)"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>reduce</h4> |
| <pre class="methodSignature"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> reduce​(<a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> adder, |
| <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> subtractor, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</pre> |
| <div class="block">Combine the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| Records with <code>null</code> key 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.Aggregator,org.apache.kafka.streams.kstream.Materialized)"><code>aggregate(Initializer, Aggregator, Aggregator, Materialized)</code></a>). |
| The result is written into a local <a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the provided <code>queryableStoreName</code>. |
| 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> |
| Each update to the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> results in a two step update of the result <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>adder</code></a> is applied for each update record and computes a new aggregate using the |
| current aggregate (first argument) and the record's value (second argument) by adding the new record to the |
| aggregate. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>subtractor</code></a> is applied for each "replaced" record of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> |
| and computes a new aggregate using the current aggregate (first argument) and the record's value (second |
| argument) by "removing" the "replaced" record from the aggregate. |
| If there is no current aggregate the <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> is not applied and the new aggregate will be the record's |
| value as-is. |
| Thus, <code>reduce(Reducer, Reducer, String)</code> can be used to compute aggregate functions like sum. |
| For sum, the adder and subtractor would work as follows: |
| <pre><code> |
| public class SumAdder implements Reducer<Integer> { |
| public Integer apply(Integer currentAgg, Integer newValue) { |
| return currentAgg + newValue; |
| } |
| } |
| |
| public class SumSubtractor implements Reducer<Integer> { |
| public Integer apply(Integer currentAgg, Integer oldValue) { |
| return currentAgg - oldValue; |
| } |
| } |
| </code></pre> |
| Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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/ReadOnlyKeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>ReadOnlyKeyValueStore</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 = ... // counting words |
| ReadOnlyKeyValueStore<K, ValueAndTimestamp<V>> localStore = streams.store(queryableStoreName, QueryableStoreTypes.<K, ValueAndTimestamp<V>> timestampedKeyValueStore()); |
| K key = "some-word"; |
| ValueAndTimestamp<V> reduceForWord = localStore.get(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#allMetadata()"><code>KafkaStreams.allMetadata()</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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>adder</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that adds a new value to the aggregate result</dd> |
| <dd><code>subtractor</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that removed an old value from the aggregate result</dd> |
| <dd><code>materialized</code> - the instance of <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> used to materialize the state store. Cannot be <code>null</code></dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>reduce</h4> |
| <pre class="methodSignature"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> reduce​(<a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> adder, |
| <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> subtractor, |
| <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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</pre> |
| <div class="block">Combine the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| Records with <code>null</code> key 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.Aggregator,org.apache.kafka.streams.kstream.Materialized)"><code>aggregate(Initializer, Aggregator, Aggregator, Materialized)</code></a>). |
| The result is written into a local <a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the provided <code>queryableStoreName</code>. |
| 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> |
| Each update to the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> results in a two step update of the result <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>adder</code></a> is applied for each update record and computes a new aggregate using the |
| current aggregate (first argument) and the record's value (second argument) by adding the new record to the |
| aggregate. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>subtractor</code></a> is applied for each "replaced" record of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> |
| and computes a new aggregate using the current aggregate (first argument) and the record's value (second |
| argument) by "removing" the "replaced" record from the aggregate. |
| If there is no current aggregate the <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> is not applied and the new aggregate will be the record's |
| value as-is. |
| Thus, <code>reduce(Reducer, Reducer, String)</code> can be used to compute aggregate functions like sum. |
| For sum, the adder and subtractor would work as follows: |
| <pre><code> |
| public class SumAdder implements Reducer<Integer> { |
| public Integer apply(Integer currentAgg, Integer newValue) { |
| return currentAgg + newValue; |
| } |
| } |
| |
| public class SumSubtractor implements Reducer<Integer> { |
| public Integer apply(Integer currentAgg, Integer oldValue) { |
| return currentAgg - oldValue; |
| } |
| } |
| </code></pre> |
| Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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/ReadOnlyKeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>ReadOnlyKeyValueStore</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 = ... // counting words |
| ReadOnlyKeyValueStore<K, ValueAndTimestamp<V>> localStore = streams.store(queryableStoreName, QueryableStoreTypes.<K, ValueAndTimestamp<V>> timestampedKeyValueStore()); |
| K key = "some-word"; |
| ValueAndTimestamp<V> reduceForWord = localStore.get(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#allMetadata()"><code>KafkaStreams.allMetadata()</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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>adder</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that adds a new value to the aggregate result</dd> |
| <dd><code>subtractor</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that removed an old value from the aggregate result</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</dd> |
| <dd><code>materialized</code> - the instance of <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> used to materialize the state store. Cannot be <code>null</code></dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Reducer)"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>reduce</h4> |
| <pre class="methodSignature"><a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> reduce​(<a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> adder, |
| <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream">Reducer</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>> subtractor)</pre> |
| <div class="block">Combine the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| Records with <code>null</code> key 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.Aggregator)"><code>aggregate(Initializer, Aggregator, Aggregator)</code></a>). |
| The result is written into a local <a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</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> |
| Each update to the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> results in a two step update of the result <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>adder</code></a> is applied for each update record and computes a new aggregate using the |
| current aggregate and the record's value by adding the new record to the aggregate. |
| The specified <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>subtractor</code></a> is applied for each "replaced" record of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> |
| and computes a new aggregate using the current aggregate and the record's value by "removing" the "replaced" |
| record from the aggregate. |
| If there is no current aggregate the <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> is not applied and the new aggregate will be the record's |
| value as-is. |
| Thus, <code>reduce(Reducer, Reducer)</code> can be used to compute aggregate functions like sum. |
| For sum, the adder and subtractor would work as follows: |
| <pre><code> |
| public class SumAdder implements Reducer<Integer> { |
| public Integer apply(Integer currentAgg, Integer newValue) { |
| return currentAgg + newValue; |
| } |
| } |
| |
| public class SumSubtractor implements Reducer<Integer> { |
| public Integer apply(Integer currentAgg, Integer oldValue) { |
| return currentAgg - oldValue; |
| } |
| } |
| </code></pre> |
| Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>adder</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that adds a new value to the aggregate result</dd> |
| <dd><code>subtractor</code> - a <a href="Reducer.html" title="interface in org.apache.kafka.streams.kstream"><code>Reducer</code></a> that removed an old value from the aggregate result</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Materialized)"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>aggregate</h4> |
| <pre class="methodSignature"><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR> aggregate​(<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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> adder, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> subtractor, |
| <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream">Materialized</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</pre> |
| <div class="block">Aggregate the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| Records with <code>null</code> key are ignored. |
| Aggregating is a generalization of <a href="#reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Materialized)"><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/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the provided <code>queryableStoreName</code>. |
| 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 once directly before the first input record is processed to |
| provide an initial intermediate aggregation result that is used to process the first record. |
| Each update to the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> results in a two step update of the result <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| The specified <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>adder</code></a> is applied for each update 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 by adding the new record to the aggregate. |
| The specified <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>subtractor</code></a> is applied for each "replaced" record of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> |
| and computes a new aggregate using the current aggregate and the record's value by "removing" the "replaced" |
| record from the aggregate. |
| Thus, <code>aggregate(Initializer, Aggregator, Aggregator, Materialized)</code> can be used to compute aggregate functions |
| like sum. |
| For sum, the initializer, adder, and subtractor would work as follows: |
| <pre><code> |
| // in this example, LongSerde.class must be set as value serde in Materialized#withValueSerde |
| public class SumInitializer implements Initializer<Long> { |
| public Long apply() { |
| return 0L; |
| } |
| } |
| |
| public class SumAdder implements Aggregator<String, Integer, Long> { |
| public Long apply(String key, Integer newValue, Long aggregate) { |
| return aggregate + newValue; |
| } |
| } |
| |
| public class SumSubtractor implements Aggregator<String, Integer, Long> { |
| public Long apply(String key, Integer oldValue, Long aggregate) { |
| return aggregate - oldValue; |
| } |
| } |
| </code></pre> |
| Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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/ReadOnlyKeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>ReadOnlyKeyValueStore</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 = ... // counting words |
| ReadOnlyKeyValueStore<K, ValueAndTimestamp<VR>> localStore = streams.store(queryableStoreName, QueryableStoreTypes.<K, ValueAndTimestamp<VR>> timestampedKeyValueStore()); |
| K key = "some-word"; |
| ValueAndTimestamp<VR> aggregateForWord = localStore.get(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#allMetadata()"><code>KafkaStreams.allMetadata()</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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Type Parameters:</span></dt> |
| <dd><code>VR</code> - the value type of the aggregated <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a></dd> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>initializer</code> - an <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> that provides an initial aggregate result value</dd> |
| <dd><code>adder</code> - an <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that adds a new record to the aggregate result</dd> |
| <dd><code>subtractor</code> - an <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that removed an old record from the aggregate result</dd> |
| <dd><code>materialized</code> - the instance of <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> used to materialize the state store. Cannot be <code>null</code></dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Named,org.apache.kafka.streams.kstream.Materialized)"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>aggregate</h4> |
| <pre class="methodSignature"><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR> aggregate​(<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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> adder, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> subtractor, |
| <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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR,​<a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state">KeyValueStore</a><org.apache.kafka.common.utils.Bytes,​byte[]>> materialized)</pre> |
| <div class="block">Aggregate the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| Records with <code>null</code> key are ignored. |
| Aggregating is a generalization of <a href="#reduce(org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Reducer,org.apache.kafka.streams.kstream.Materialized)"><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/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</code></a> (which is basically an ever-updating materialized view) |
| that can be queried using the provided <code>queryableStoreName</code>. |
| 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 once directly before the first input record is processed to |
| provide an initial intermediate aggregation result that is used to process the first record. |
| Each update to the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> results in a two step update of the result <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| The specified <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>adder</code></a> is applied for each update 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 by adding the new record to the aggregate. |
| The specified <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>subtractor</code></a> is applied for each "replaced" record of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> |
| and computes a new aggregate using the current aggregate and the record's value by "removing" the "replaced" |
| record from the aggregate. |
| Thus, <code>aggregate(Initializer, Aggregator, Aggregator, Materialized)</code> can be used to compute aggregate functions |
| like sum. |
| For sum, the initializer, adder, and subtractor would work as follows: |
| <pre><code> |
| // in this example, LongSerde.class must be set as value serde in Materialized#withValueSerde |
| public class SumInitializer implements Initializer<Long> { |
| public Long apply() { |
| return 0L; |
| } |
| } |
| |
| public class SumAdder implements Aggregator<String, Integer, Long> { |
| public Long apply(String key, Integer newValue, Long aggregate) { |
| return aggregate + newValue; |
| } |
| } |
| |
| public class SumSubtractor implements Aggregator<String, Integer, Long> { |
| public Long apply(String key, Integer oldValue, Long aggregate) { |
| return aggregate - oldValue; |
| } |
| } |
| </code></pre> |
| Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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/ReadOnlyKeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>ReadOnlyKeyValueStore</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 = ... // counting words |
| ReadOnlyKeyValueStore<K, ValueAndTimestamp<VR>> localStore = streams.store(queryableStoreName, QueryableStoreTypes.<K, ValueAndTimestamp<VR>> timestampedKeyValueStore()); |
| K key = "some-word"; |
| ValueAndTimestamp<VR> aggregateForWord = localStore.get(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#allMetadata()"><code>KafkaStreams.allMetadata()</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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Type Parameters:</span></dt> |
| <dd><code>VR</code> - the value type of the aggregated <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a></dd> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>initializer</code> - an <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> that provides an initial aggregate result value</dd> |
| <dd><code>adder</code> - an <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that adds a new record to the aggregate result</dd> |
| <dd><code>subtractor</code> - an <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that removed an old record from the aggregate result</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</dd> |
| <dd><code>materialized</code> - the instance of <a href="Materialized.html" title="class in org.apache.kafka.streams.kstream"><code>Materialized</code></a> used to materialize the state store. Cannot be <code>null</code></dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator)"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>aggregate</h4> |
| <pre class="methodSignature"><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR> aggregate​(<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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> adder, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> subtractor)</pre> |
| <div class="block">Aggregate the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> using default serializers and deserializers. |
| Records with <code>null</code> key are ignored. |
| Aggregating is a generalization of <a href="#reduce(org.apache.kafka.streams.kstream.Reducer,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. |
| If the result value type does not match the <a href="../StreamsConfig.html#DEFAULT_VALUE_SERDE_CLASS_CONFIG"><code>default value |
| serde</code></a> you should use <a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Materialized)"><code>aggregate(Initializer, Aggregator, Aggregator, Materialized)</code></a>. |
| The result is written into a local <a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</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 once directly before the first input record is processed to |
| provide an initial intermediate aggregation result that is used to process the first record. |
| Each update to the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> results in a two step update of the result <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| The specified <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>adder</code></a> is applied for each update 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 by adding the new record to the aggregate. |
| The specified <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>subtractor</code></a> is applied for each "replaced" record of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> |
| and computes a new aggregate using the current aggregate and the record's value by "removing" the "replaced" |
| record from the aggregate. |
| Thus, <code>aggregate(Initializer, Aggregator, Aggregator, String)</code> can be used to compute aggregate functions |
| like sum. |
| For sum, the initializer, adder, and subtractor would work as follows: |
| <pre><code> |
| // in this example, LongSerde.class must be set as default value serde in StreamsConfig |
| public class SumInitializer implements Initializer<Long> { |
| public Long apply() { |
| return 0L; |
| } |
| } |
| |
| public class SumAdder implements Aggregator<String, Integer, Long> { |
| public Long apply(String key, Integer newValue, Long aggregate) { |
| return aggregate + newValue; |
| } |
| } |
| |
| public class SumSubtractor implements Aggregator<String, Integer, Long> { |
| public Long apply(String key, Integer oldValue, Long aggregate) { |
| return aggregate - oldValue; |
| } |
| } |
| </code></pre> |
| Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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>. |
| 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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Type Parameters:</span></dt> |
| <dd><code>VR</code> - the value type of the aggregated <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a></dd> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>initializer</code> - a <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> that provides an initial aggregate result value</dd> |
| <dd><code>adder</code> - a <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that adds a new record to the aggregate result</dd> |
| <dd><code>subtractor</code> - a <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that removed an old record from the aggregate result</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Named)"> |
| <!-- --> |
| </a> |
| <ul class="blockListLast"> |
| <li class="blockList"> |
| <h4>aggregate</h4> |
| <pre class="methodSignature"><VR> <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream">KTable</a><<a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​VR> aggregate​(<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="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> adder, |
| <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream">Aggregator</a><? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">K</a>,​? super <a href="KGroupedTable.html" title="type parameter in KGroupedTable">V</a>,​VR> subtractor, |
| <a href="Named.html" title="class in org.apache.kafka.streams.kstream">Named</a> named)</pre> |
| <div class="block">Aggregate the value of records of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> that got <a href="KTable.html#groupBy(org.apache.kafka.streams.kstream.KeyValueMapper)"><code>mapped</code></a> to the same key into a new instance of <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> using default serializers and deserializers. |
| Records with <code>null</code> key are ignored. |
| Aggregating is a generalization of <a href="#reduce(org.apache.kafka.streams.kstream.Reducer,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. |
| If the result value type does not match the <a href="../StreamsConfig.html#DEFAULT_VALUE_SERDE_CLASS_CONFIG"><code>default value |
| serde</code></a> you should use <a href="#aggregate(org.apache.kafka.streams.kstream.Initializer,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Aggregator,org.apache.kafka.streams.kstream.Materialized)"><code>aggregate(Initializer, Aggregator, Aggregator, Materialized)</code></a>. |
| The result is written into a local <a href="../state/KeyValueStore.html" title="interface in org.apache.kafka.streams.state"><code>KeyValueStore</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 once directly before the first input record is processed to |
| provide an initial intermediate aggregation result that is used to process the first record. |
| Each update to the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> results in a two step update of the result <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a>. |
| The specified <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>adder</code></a> is applied for each update 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 by adding the new record to the aggregate. |
| The specified <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>subtractor</code></a> is applied for each "replaced" record of the original <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a> |
| and computes a new aggregate using the current aggregate and the record's value by "removing" the "replaced" |
| record from the aggregate. |
| Thus, <code>aggregate(Initializer, Aggregator, Aggregator, String)</code> can be used to compute aggregate functions |
| like sum. |
| For sum, the initializer, adder, and subtractor would work as follows: |
| <pre><code> |
| // in this example, LongSerde.class must be set as default value serde in StreamsConfig |
| public class SumInitializer implements Initializer<Long> { |
| public Long apply() { |
| return 0L; |
| } |
| } |
| |
| public class SumAdder implements Aggregator<String, Integer, Long> { |
| public Long apply(String key, Integer newValue, Long aggregate) { |
| return aggregate + newValue; |
| } |
| } |
| |
| public class SumSubtractor implements Aggregator<String, Integer, Long> { |
| public Long apply(String key, Integer oldValue, Long aggregate) { |
| return aggregate - oldValue; |
| } |
| } |
| </code></pre> |
| Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to |
| the same key. |
| The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of |
| parallel running Kafka Streams instances, and the <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>. |
| 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. |
| |
| You can retrieve all generated internal topic names via <a href="../Topology.html#describe()"><code>Topology.describe()</code></a>.</div> |
| <dl> |
| <dt><span class="paramLabel">Type Parameters:</span></dt> |
| <dd><code>VR</code> - the value type of the aggregated <a href="KTable.html" title="interface in org.apache.kafka.streams.kstream"><code>KTable</code></a></dd> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>initializer</code> - a <a href="Initializer.html" title="interface in org.apache.kafka.streams.kstream"><code>Initializer</code></a> that provides an initial aggregate result value</dd> |
| <dd><code>adder</code> - a <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that adds a new record to the aggregate result</dd> |
| <dd><code>subtractor</code> - a <a href="Aggregator.html" title="interface in org.apache.kafka.streams.kstream"><code>Aggregator</code></a> that removed an old record from the aggregate result</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</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>a <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</dd> |
| </dl> |
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