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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 14:08:47 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15874581#comment-15874581
] 

ASF GitHub Bot commented on FLINK-4856:
---------------------------------------

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

    https://github.com/apache/flink/pull/3336#discussion_r101990286
  
    --- Diff: flink-core/src/main/java/org/apache/flink/api/common/typeutils/base/MapSerializer.java
---
    @@ -0,0 +1,179 @@
    +/*
    + * 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.typeutils.base;
    +
    +import org.apache.flink.api.common.typeutils.TypeSerializer;
    +import org.apache.flink.core.memory.DataInputView;
    +import org.apache.flink.core.memory.DataOutputView;
    +import org.apache.flink.util.Preconditions;
    +
    +import java.io.IOException;
    +import java.util.HashMap;
    +import java.util.List;
    +import java.util.Map;
    +
    +/**
    + * A serializer for {@link List Lists}. The serializer relies on an element serializer
    + * for teh serialization of the list's elements.
    + *
    + * <p>The serialization format for the list is as follows: four bytes for the length
of the lost,
    + * followed by the serialized representation of each element.
    + *
    + * @param <K> The type of the keys in the map.
    + * @param <V> The type of the values in the map.
    + */
    +public class MapSerializer<K, V> extends TypeSerializer<Map<K, V>>
{
    --- End diff --
    
    You should also add a test for the serializer itself. Testing all the functions comes
almost for free by extending``SerializerTestBase``.


> 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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