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From: chandnisingh <git@git.apache.org>
To: dev@apex.incubator.apache.org
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References: <git-pr-187-incubator-apex-core@git.apache.org>
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Subject: [GitHub] incubator-apex-core pull request: Checkpoint notification to
 notif...
Content-Type: text/plain
Message-Id: <20151217234050.4EB93E6967@git1-us-west.apache.org>
Date: Thu, 17 Dec 2015 23:40:50 +0000 (UTC)

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

    https://github.com/apache/incubator-apex-core/pull/187#discussion_r47977582
  
    --- Diff: api/src/main/java/com/datatorrent/api/Operator.java ---
    @@ -270,4 +271,29 @@ public String toString()
     
       }
     
    +  /**
    +   * Operators that need to be notified about checkpoint events should implement this interface.
    +   *
    +   * The notification callbacks in this interface are called outside window boundaries so the operators should not
    +   * attempt to send any tuples in these callbacks.
    +   *
    +   */
    +  public static interface CheckpointNotificationListener extends CheckpointListener
    +  {
    +    /**
    +     * Notify the operator that a checkpoint is about to be performed.
    +     *
    +     * Operators may need to perform certain tasks just before a checkpoint such as calling flush on a stream. Having
    +     * this notification helps operators perform such operations optimally by doing them once before checkpoint as
    +     * opposed to doing it repeatedly at the end of every window.
    +     *
    +     * The method will be called before the checkpoint is performed. It will be called after
    +     * {@link Operator#endWindow()} call of the window preceding the checkpoint and before the checkpoint is
    +     * actually performed.
    +     *
    +     * @param windowId The window id of the window preceding the checkpoint
    +     */
    +    public void checkpoint(long windowId);
    --- End diff --
    
    @PramodSSImmaneni Sorry couldn't complete the comment. Incremental checkpointing may require windowId  because it is the operator which is writing the difference in state corresponding to a window id. 


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