Github user PramodSSImmaneni commented on a diff in the pull request:
https://github.com/apache/incubator-apex-core/pull/187#discussion_r47976721
--- 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 --
@chandnisingh good point. However can you think of a use case where you
would need to identify more than one set of state slices between checkpoints
distinctly at the same time. If that is not the case and the old slices are
cleaned up then we can reuse the same windowId from beginWindow to identify all
of them.
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