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https://issues.apache.org/jira/browse/FLINK-6034?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15938144#comment-15938144
 ] 

ASF GitHub Bot commented on FLINK-6034:
---------------------------------------

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

    https://github.com/apache/flink/pull/3531#discussion_r107646429
  
    --- Diff: 
flink-runtime/src/main/java/org/apache/flink/runtime/checkpoint/StateAssignmentOperation.java
 ---
    @@ -306,6 +307,29 @@ private static void 
assignTaskStatesToOperatorInstances(
        }
     
        /**
    +    * Determine the subset of {@link KeyGroupsStateHandle 
KeyGroupsStateHandles} with correct
    +    * key group index for the given subtask {@link KeyGroupRange}.
    +    * <p>
    +    * <p>This is publicly visible to be used in tests.
    +    */
    +   public static List<KeyedStateHandle> getKeyedStateHandles(
    +                   Collection<? extends KeyedStateHandle> 
keyedStateHandles,
    +                   KeyGroupRange subtaskKeyGroupRange) {
    +
    +           List<KeyedStateHandle> subtaskKeyedStateHandles = new 
ArrayList<>();
    +
    +           for (KeyedStateHandle keyedStateHandle : keyedStateHandles) {
    +                   KeyGroupRange intersection = 
keyedStateHandle.getKeyGroupRange().getIntersection(subtaskKeyGroupRange);
    --- End diff --
    
    The idea is great! It does make sense to allow a `KeyedStateHandle` to 
create a new `KeyedStateHandle` to the states of the sub range. I will update 
the PR as suggested.


> Add KeyedStateHandle for the snapshots in keyed streams
> -------------------------------------------------------
>
>                 Key: FLINK-6034
>                 URL: https://issues.apache.org/jira/browse/FLINK-6034
>             Project: Flink
>          Issue Type: Sub-task
>          Components: State Backends, Checkpointing
>            Reporter: Xiaogang Shi
>            Assignee: Xiaogang Shi
>
> Currently, the only type of the snapshots in keyed streams is 
> {{KeyGroupsStateHandle}} which is full and store the states one group after 
> another. With the introduction of incremental checkpointing, we need a higher 
> level abstraction of keyed snapshots to allow flexible snapshot formats. 
> The implementation of {{KeyedStateHandle}} s may vary a lot in different 
> backends. The only information needed in {{KeyedStateHandle}} s is their key 
> group range. When recovering the job with a different degree of parallelism, 
> {{KeyedStateHandle}} s will be assigned to those subtasks whose key group 
> ranges overlap with their ranges.



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