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https://issues.apache.org/jira/browse/FLINK-9487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16511454#comment-16511454
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ASF GitHub Bot commented on FLINK-9487:
---------------------------------------

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

    https://github.com/apache/flink/pull/6159#discussion_r195168815
  
    --- Diff: 
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/InternalTimerHeap.java
 ---
    @@ -224,6 +227,15 @@ void bulkAddRestoredTimers(Collection<? extends 
InternalTimer<K, N>> restoredTim
                return result;
        }
     
    +   @Nonnull
    +   StateSnapshot snapshot(TimerHeapInternalTimer.TimerSerializer<K, N> 
serializer) {
    +           return new InternalTimerHeapSnapshot<>(
    +                   Arrays.copyOfRange(queue, 1, size + 1),
    +                   serializer,
    --- End diff --
    
    The `serializer` was be duplicated here or in the constructor of 
`InternalTimerHeapSnapshot` in the current code, do you plan to duplicate it 
when calling the `snapshot()` in the next code?


> Prepare InternalTimerHeap for asynchronous snapshots
> ----------------------------------------------------
>
>                 Key: FLINK-9487
>                 URL: https://issues.apache.org/jira/browse/FLINK-9487
>             Project: Flink
>          Issue Type: Sub-task
>          Components: State Backends, Checkpointing, Streaming
>            Reporter: Stefan Richter
>            Assignee: Stefan Richter
>            Priority: Major
>             Fix For: 1.6.0
>
>
> When we want to snapshot timers with the keyed backend state, this must 
> happen as part of an asynchronous snapshot.
> The data structure {{InternalTimerHeap}} needs to offer support for this 
> through a lightweight copy mechanism (e.g. arraycopy of the timer queue, 
> because timers are immutable w.r.t. serialization).
> We can also stop keeping the dedup maps in {{InternalTimerHeap}} separated by 
> key-group, all timers can go into one map.
> Instead, we can implement online-partitioning as part of the asynchronous 
> operation, similar to what we do in {{CopyOnWriteStateTable}} snapshots. 
> Notice that in this intermediate state, the code will still run in the 
> synchronous part until we are integrated with the backends for async 
> snapshotting (next subtask of this jira).



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