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From Tushar Gosavi <tus...@datatorrent.com>
Subject Re: [DISCUSSION] Custom Control Tuples
Date Fri, 24 Jun 2016 19:03:59 GMT
+1 for the feature

I am in favor of option 1, but we may need an helper method to avoid
compiler error on typed port, as calling port.emit(controlTuple) will
be an error if type of control tuple and port does not match. or new
method in outputPort object , emitControlTuple(ControlTuple).

Can you give example of piggy backing tuple with current BEGIN_WINDOW
and END_WINDOW control tuples?

In case of NxM partitioning, each downstream operator will receive N
control tuples. will it call user handler N times for each downstream
operator or just once.

Regards,
- Tushar.



On Fri, Jun 24, 2016 at 11:52 PM, David Yan <david@datatorrent.com> wrote:
> Hi all,
>
> I would like to propose a new feature to the Apex core engine -- the
> support of custom control tuples. Currently, we have control tuples such as
> BEGIN_WINDOW, END_WINDOW, CHECKPOINT, and so on, but we don't have the
> support for applications to insert their own control tuples. The way
> currently to get around this is to use data tuples and have a separate port
> for such tuples that sends tuples to all partitions of the downstream
> operators, which is not exactly developer friendly.
>
> We have already seen a number of use cases that can use this feature:
>
> 1) Batch support: We need to tell all operators of the physical DAG when a
> batch starts and ends, so the operators can do whatever that is needed upon
> the start or the end of a batch.
>
> 2) Watermark: To support the concepts of event time windowing, the
> watermark control tuple is needed to tell which windows should be
> considered late.
>
> 3) Changing operator properties: We do have the support of changing
> operator properties on the fly, but with a custom control tuple, the
> command to change operator properties can be window aligned for all
> partitions and also across the DAG.
>
> 4) Recording tuples: Like changing operator properties, we do have this
> support now but only at the individual physical operator level, and without
> control of which window to record tuples for. With a custom control tuple,
> because a control tuple must belong to a window, all operators in the DAG
> can start (and stop) recording for the same windows.
>
> I can think of two options to achieve this:
>
> 1) new custom control tuple type that takes user's serializable object.
>
> 2) piggy back the current BEGIN_WINDOW and END_WINDOW control tuples.
>
> Please provide your feedback. Thank you.
>
> David

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