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From aljoscha <...@git.apache.org>
Subject [GitHub] flink pull request #5230: [FLINK-8345] Add iterator of keyed state on broadc...
Date Thu, 25 Jan 2018 14:12:30 GMT
Github user aljoscha commented on a diff in the pull request:

    --- Diff: flink-core/src/main/java/org/apache/flink/api/common/state/BroadcastState.java
    @@ -0,0 +1,48 @@
    + * 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.flink.api.common.state;
    +import org.apache.flink.annotation.PublicEvolving;
    +import java.util.Map;
    + * A type of state that can be created to store the state of a {@code BroadcastStream}.
This state assumes that
    + * <b>the same elements are sent to all instances of an operator.</b>
    + *
    + * <p><b>CAUTION:</b> the user has to guarantee that all task instances
store the same elements in this type of state.
    + *
    + * <p> Each operator instance individually maintains and stores elements in the
broadcast state. The fact that the
    + * incoming stream is a broadcast one guarantees that all instances see all the elements.
Upon recovery
    + * or re-scaling, the same state is given to each of the instances. To avoid hotspots,
each task reads its previous
    + * partition, and if there are more tasks (scale up), then the new instances read from
the old instances in a round
    + * robin fashion. This is why each instance has to guarantee that it stores the same
elements as the rest. If not,
    + * upon recovery or rescaling you may have unpredictable redistribution of the partitions,
thus unpredictable results.
    + *
    + * @param <K> The key type of the elements in the {@link BroadcastState}.
    + * @param <V> The value type of the elements in the {@link BroadcastState}.
    + */
    +public interface BroadcastState<K, V> extends MapState<K, V> {
    +	/**
    +	 * @return An {@link Iterable} over the entries in the state with <b>read-only</b>
    +	 */
    +	Iterable<Map.Entry<K, V>> unmodifiableEntriesIt() throws Exception;
    --- End diff --
    I would prefer `unmodifiableEntries` or better `immutableEntries` here. And I think having
a Javadoc comment without an actual body is not typical, maybe just go for `Returns an immutable
{@link Iterable} over the entries in the state.`


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