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https://issues.apache.org/jira/browse/APEXCORE-581?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15716101#comment-15716101
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Vlad Rozov commented on APEXCORE-581:
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Agree, GenericNode needs to orchestrate tuples the same way what it currently
does. The same applies to the Buffer Server. I foresee code changes both to
GenericNode and to the Buffer Server needed to support custom control tuples.
> Delivery of Custom Control Tuples
> ---------------------------------
>
> Key: APEXCORE-581
> URL: https://issues.apache.org/jira/browse/APEXCORE-581
> Project: Apache Apex Core
> Issue Type: Sub-task
> Reporter: David Yan
>
> The behavior should be as follow:
> - The control tuples should only be sent to downstream at streaming window
> boundaries
> - The control tuples should be sent to all partitions downstream
> - The control tuples should be sent in the same order of arrival.
> - Within a streaming window, do not send the same control tuple twice, even
> if the same control tuple is received multiple times within that window. This
> is possible if the operator has two input ports. (The LinkedHashMap should be
> easily able to ensure both order and uniqueness.)
> - The delivery of control tuples needs to stop at DelayOperator.
> - When a streaming window is committed, remove the associated LinkedHashMap
> that belong to windows with IDs that are less than the committed window
> - It's safe to assume the control tuples are rare enough and can fit in memory
> This will involve an additional MessageType to represent a custom control
> tuple.
> We probably need to have a data structure (possibly a LinkedHashMap) per
> streaming window that stores the control tuple in the buffer server.
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