[jira] [Commented] (FLINK-9487) Prepare InternalTimerHeap for asynchronous snapshots

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

    [ https://issues.apache.org/jira/browse/FLINK-9487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16511139#comment-16511139 ] 

ASF GitHub Bot commented on FLINK-9487:
---------------------------------------

GitHub user StefanRRichter opened a pull request:

    https://github.com/apache/flink/pull/6159

    [FLINK-9487] Prepare InternalTimerHeap for asynchronous snapshots

    ## What is the purpose of the change
    
    This PR is the first step in the context of FLINK-9485. Purpose of this PR is to enhance ``InternalTimerHeap`` with the capability to produce asynchronous snapshots. This is very similar to the approach of asynchronous snapshots for the ``CopyOnWriteStateTable`` and we want to reuse as much of the existing code as possible to power both instances of snapshots. 
    
    
    ## Brief change log
    
    The first commit generalizes the key-group-partitioning algorithm for async snapshots from the ``CopyOnWriteStateTable``. The newly introduced ``StateSnapshot`` interface outlines the asynchronous snapshot life-cycle, which typically looks as follows. In the synchronous part of a checkpoint, an instance of {StateSnapshot} is produced for a state and captures the state at this point in time. Then, in the asynchronous part of the checkpoint, the user calls `` #partitionByKeyGroup()`` to ensure that the snapshot is partitioned into key-groups. For state that is already partitioned, this can be a NOP. The returned ``KeyGroupPartitionedSnapshot`` can be used by the caller to write the state by key-group. As a last step, when the state is completely written, the user calls ``#release()``.
    
    The partitioning algorithm is also slightly modified to cache computed key-group-ids per element. This is improves runtime at the cost of some additional memory.
    
    The second commit introduced an implementation of ``StateSnapshot`` for the ``InternalTimerHeap`` data structure.
    
    
    ## Verifying this change
    
    This change added tests: ``TimerPartitionerTest`` , ``StateTableKeyGroupPartitionerTest``, ``AbstractKeyGroupPartitionedSnapshotTest``
    
    
    ## Does this pull request potentially affect one of the following parts:
    
      - Dependencies (does it add or upgrade a dependency): (no)
      - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (no)
      - The serializers: (no)
      - The runtime per-record code paths (performance sensitive): (no)
      - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes)
      - The S3 file system connector: (no)
    
    ## Documentation
    
      - Does this pull request introduce a new feature? (yes)
      - If yes, how is the feature documented? (not applicable)


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/StefanRRichter/flink FLINK-9487

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/flink/pull/6159.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #6159
    
----
commit 9e95e1a5f36b6c4f0b021f38b2a2a4c2f8dacf3a
Author: Stefan Richter <s....@...>
Date:   2018-06-11T12:48:06Z

    Refactor/generalize key-group partitioning.

commit 800abd9743c5483f50835d0cf938ad50f550ae49
Author: Stefan Richter <s....@...>
Date:   2018-06-11T15:44:10Z

    Introduce TimerHeap snapshots and key-group-partitioning

----


> 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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