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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.kafka.streams.kstream;

import org.apache.kafka.streams.KafkaStreams;
import org.apache.kafka.streams.KeyValue;
import org.apache.kafka.streams.StreamsBuilder;
import org.apache.kafka.streams.state.ReadOnlyKeyValueStore;

/**
 * {@code GlobalKTable} is an abstraction of a changelog stream from a primary-keyed table.
 * Each record in this changelog stream is an update on the primary-keyed table with the record key as the primary key.
 * 

* {@code GlobalKTable} can only be used as right-hand side input for {@link KStream stream}-table joins. *

* In contrast to a {@link KTable} that is partitioned over all {@link KafkaStreams} instances, a {@code GlobalKTable} * is fully replicated per {@link KafkaStreams} instance. * Every partition of the underlying topic is consumed by each {@code GlobalKTable}, such that the full set of data is * available in every {@link KafkaStreams} instance. * This provides the ability to perform joins with {@link KStream} without having to repartition the input stream. * All joins with the {@code GlobalKTable} require that a {@link KeyValueMapper} is provided that can map from the * {@link KeyValue} of the left hand side {@link KStream} to the key of the right hand side {@code GlobalKTable}. *

* A {@code GlobalKTable} is created via a {@link StreamsBuilder}. For example: *

{@code
 * builder.globalTable("topic-name", "queryable-store-name");
 * }
* all {@code GlobalKTable}s are backed by a {@link ReadOnlyKeyValueStore} and are therefore queryable via the * interactive queries API. * For example: *
{@code
 * final GlobalKTable globalOne = builder.globalTable("g1", "g1-store");
 * final GlobalKTable globalTwo = builder.globalTable("g2", "g2-store");
 * ...
 * final KafkaStreams streams = ...;
 * streams.start()
 * ...
 * ReadOnlyKeyValueStore view = streams.store("g1-store", QueryableStoreTypes.timestampedKeyValueStore());
 * view.get(key); // can be done on any key, as all keys are present
 *}
* Note that in contrast to {@link KTable} a {@code GlobalKTable}'s state holds a full copy of the underlying topic, * thus all keys can be queried locally. *

* Records from the source topic that have null keys are dropped. * * @param Type of primary keys * @param Type of value changes * @see KTable * @see StreamsBuilder#globalTable(String) * @see KStream#join(GlobalKTable, KeyValueMapper, ValueJoiner) * @see KStream#leftJoin(GlobalKTable, KeyValueMapper, ValueJoiner) */ public interface GlobalKTable { /** * Get the name of the local state store that can be used to query this {@code GlobalKTable}. * * @return the underlying state store name, or {@code null} if this {@code GlobalKTable} cannot be queried. */ String queryableStoreName(); }





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