[jira] [Commented] (FLINK-8360) Implement task-local state recovery

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-8360?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16348132#comment-16348132 ] 

ASF GitHub Bot commented on FLINK-8360:
---------------------------------------

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

    https://github.com/apache/flink/pull/5239#discussion_r165275719
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/state/StateSnapshotContextSynchronousImpl.java ---
    @@ -109,14 +109,20 @@ public OperatorStateCheckpointOutputStream getRawOperatorStateOutput() throws Ex
     		return operatorStateCheckpointOutputStream;
     	}
     
    -	public RunnableFuture<KeyedStateHandle> getKeyedStateStreamFuture() throws IOException {
    -		KeyGroupsStateHandle keyGroupsStateHandle = closeAndUnregisterStreamToObtainStateHandle(keyedStateCheckpointOutputStream);
    -		return new DoneFuture<KeyedStateHandle>(keyGroupsStateHandle);
    +	public RunnableFuture<SnapshotResult<KeyedStateHandle>> getKeyedStateStreamFuture() throws IOException {
    +		return getGenericStateStreamFuture(keyedStateCheckpointOutputStream);
     	}
     
    -	public RunnableFuture<OperatorStateHandle> getOperatorStateStreamFuture() throws IOException {
    -		OperatorStateHandle operatorStateHandle = closeAndUnregisterStreamToObtainStateHandle(operatorStateCheckpointOutputStream);
    -		return new DoneFuture<>(operatorStateHandle);
    +	public RunnableFuture<SnapshotResult<OperatorStateHandle>> getOperatorStateStreamFuture() throws IOException {
    +		return getGenericStateStreamFuture(operatorStateCheckpointOutputStream);
    +	}
    +
    +	private <T extends StateObject> RunnableFuture<SnapshotResult<T>> getGenericStateStreamFuture(
    +		NonClosingCheckpointOutputStream<? extends T> stream) throws IOException {
    +		T operatorStateHandle = (T) closeAndUnregisterStreamToObtainStateHandle(stream);
    --- End diff --
    
    This cast seems a bit fishy to me. I think it should not be necessary if the generics are applied correctly. A way to solve it would be `T extends StreamStateHandle` and `RunnableFuture<? extends SnapshotResult<? extends KeyedStateHandle>> getKeyedStateStreamFuture()`


> Implement task-local state recovery
> -----------------------------------
>
>                 Key: FLINK-8360
>                 URL: https://issues.apache.org/jira/browse/FLINK-8360
>             Project: Flink
>          Issue Type: New Feature
>          Components: State Backends, Checkpointing
>            Reporter: Stefan Richter
>            Assignee: Stefan Richter
>            Priority: Major
>             Fix For: 1.5.0
>
>
> This issue tracks the development of recovery from task-local state. The main idea is to have a secondary, local copy of the checkpointed state, while there is still a primary copy in DFS that we report to the checkpoint coordinator.
> Recovery can attempt to restore from the secondary local copy, if available, to save network bandwidth. This requires that the assignment from tasks to slots is as sticky is possible.
> For starters, we will implement this feature for all managed keyed states and can easily enhance it to all other state types (e.g. operator state) later.



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