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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4856) Add MapState for keyed streams
Date Mon, 20 Feb 2017 01:37:44 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15873931#comment-15873931

ASF GitHub Bot commented on FLINK-4856:

Github user shixiaogang commented on a diff in the pull request:

    --- Diff: flink-core/src/main/java/org/apache/flink/api/common/state/MapState.java ---
    @@ -0,0 +1,111 @@
    + * 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.io.IOException;
    +import java.util.Iterator;
    +import java.util.Map;
    + * {@link State} interface for partitioned key-value state. The key-value pair can be
    + * added, updated and retrieved.
    + *
    + * <p>The state is accessed and modified by user functions, and checkpointed consistently
    + * by the system as part of the distributed snapshots.
    + *
    + * <p>The state is only accessible by functions applied on a KeyedDataStream. The
key is
    + * automatically supplied by the system, so the function always sees the value mapped
to the
    + * key of the current element. That way, the system can handle stream and state partitioning
    + * consistently together.
    + *
    + * @param <UK> Type of the keys in the state.
    + * @param <UV> Type of the values in the state.
    + */
    +public interface MapState<UK, UV> extends AppendingState<Map<UK, UV>,
Iterable<Map.Entry<UK, UV>>> {
    --- End diff --
    `MapState` provides the `add` method which puts a collection of key-value pairs into the
state. Though the semantics may be a little different in existing `AppendingState`s, I think
it's okay for `MapState` to be an `AppendingState` because the interface does not enforce
any restriction on the modification of previous data.

> Add MapState for keyed streams
> ------------------------------
>                 Key: FLINK-4856
>                 URL: https://issues.apache.org/jira/browse/FLINK-4856
>             Project: Flink
>          Issue Type: New Feature
>          Components: DataStream API, State Backends, Checkpointing
>            Reporter: Xiaogang Shi
>            Assignee: Xiaogang Shi
> Many states in keyed streams are organized as key-value pairs. Currently, these states
are implemented by storing the entire map into a ValueState or a ListState. The implementation
however is very costly because all entries have to be serialized/deserialized when updating
a single entry. To improve the efficiency of these states, MapStates are urgently needed.

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