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Date: Fri, 24 Mar 2017 10:14:41 +0000 (UTC)
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Subject: [jira] [Commented] (FLINK-6034) Add KeyedStateHandle for the
 snapshots in keyed streams
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archived-at: Fri, 24 Mar 2017 10:14:47 -0000


    [ https://issues.apache.org/jira/browse/FLINK-6034?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15940108#comment-15940108 ] 

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

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

    https://github.com/apache/flink/pull/3531#discussion_r107870871
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/checkpoint/StateAssignmentOperation.java ---
    @@ -290,19 +291,19 @@ private static void assignTaskStatesToOperatorInstances(
     	 * <p>
     	 * <p>This is publicly visible to be used in tests.
     	 */
    -	public static List<KeyGroupsStateHandle> getKeyGroupsStateHandles(
    -			Collection<KeyGroupsStateHandle> allKeyGroupsHandles,
    -			KeyGroupRange subtaskKeyGroupIds) {
    +	public static List<KeyedStateHandle> getKeyedStateHandles(
    +			Collection<? extends KeyedStateHandle> keyedStateHandles,
    +			KeyGroupRange subtaskKeyGroupRange) {
     
    -		List<KeyGroupsStateHandle> subtaskKeyGroupStates = new ArrayList<>();
    +		List<KeyedStateHandle> subtaskKeyedStateHandles = new ArrayList<>();
     
    -		for (KeyGroupsStateHandle storedKeyGroup : allKeyGroupsHandles) {
    -			KeyGroupsStateHandle intersection = storedKeyGroup.getKeyGroupIntersection(subtaskKeyGroupIds);
    -			if (intersection.getNumberOfKeyGroups() > 0) {
    -				subtaskKeyGroupStates.add(intersection);
    -			}
    +		for (KeyedStateHandle keyedStateHandle : keyedStateHandles) {
    +			KeyedStateHandle intersectedKeyedStateHandle = keyedStateHandle.getIntersection(subtaskKeyGroupRange);
    +
    +			subtaskKeyedStateHandles.add(intersectedKeyedStateHandle);
    --- End diff --
    
    I think we should only add a state handle if the key group range from the intersection is non-empty. Even though those empty handles are probably ignored later, I think it is cleaner.


> 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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