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From Bhupesh Chawda <bhup...@datatorrent.com>
Subject Re: [DISCUSS] Custom Control Tuples Design
Date Thu, 22 Dec 2016 06:10:38 GMT
Hi Vlad,

The problem in using the Tuple class as the wrapper is that the Ports
belong to the API and we want to wrap the payload object of the control
tuple into the Tuple class which is not part of the API.

The output port will just get the payload of the user control tuple. For
example, if the user emits a Long, as a control tuple, the payload object
will just be a Long object.

It is necessary to bundle this Long into some recognizable object so that
the BufferServerPublisher knows that this is a Control tuple and not a
regular tuple and serialize it accordingly. It is therefore necessary that
the tuple be part of some known hierarchy so that can be distinguished from
other payload tuples. Let us call this class ControlTupleInterface. Note
that this needs to be done before the tuple is inserted into the sink which
is done in the port objects. Once the tuple is inserted into the sink, it
would seem just like any other payload tuple and cannot be distinguished.

For this reason, I had something like the following in API:

package com.datatorrent.api;
public class ControlTupleInterface
{
  Object payload; // User control tuple payload. A Long() for example.
  UUID id;  // Unique Id to de-duplicate in downstream operators
}

Regarding your suggestion on using the Tuple class as the wrapper for the
control tuple payload, let me mention the current scenario flow to make the
discussion easier:

We have a Tuple class in buffer server which is responsible for serializing
the user control tuple bundling together a message type:
CUSTOM_CONTROL_TUPLE_VALUE.


*com.datatorrent.bufferserver.packet.Tuple|--
com.datatorrent.bufferserver.packet.CustomControlTuple*
We have another Tuple class in Stram which helps the BufferServerSubscriber
to de-serialize the serialized tuples. We should have CustomControlTuple in
stram as follows:


*com.datatorrent.stram.tuple.Tuple|--
com.datatorrent.stram.tuple.CustomControlTuple*This will have a field for
user control payload.

I think we should not expose the Tuple class in stram to the API. That was
the main reason I introduced another class/interface ControlTupleInterface
as described above.

Regarding, adding methods to DefaultInputPort and DefaultOutputPort, I
think error detection would not be early enough if the control tuple is
sent very late in the processing :-)
Extending the ports to ControlTupleAware* should help in this case.
However, we still need to see if there are any downsides on doing this.

Thanks.

~ Bhupesh




On Thu, Dec 22, 2016 at 7:26 AM, Vlad Rozov <v.rozov@datatorrent.com> wrote:

> Hi Bhupesh,
>
> it should not be a CustomWrapper.  The wrapper object should be
> CustomControlTuple that extends Tuple. There is already code that checks
> for Tuple instance. The "unWrap" name is misleading, IMO. It should be
> something like customControlTuple.getPayload() or
> customControlTuple.getAttachment(). In the emitControl(), create new
> CustomControlTuple using provided payload as one of arguments. It may still
> be good to use common parent other than Object for control tuple payload
> class hierarchy.
>
> I don't understand how adding more methods to the Default implementation
> will help with early error detection unless application or operator that
> relies on the custom control tuple functionality explicitly checks for the
> platform version at run-time or tries to emit a control tuple just to check
> that such functionality is supported by the platform.
>
> Thank you,
>
> Vlad
>
> On 12/21/16 04:58, Bhupesh Chawda wrote:
>
>> Hi Vlad.
>>
>> Yes, the API should not change. We can take an Object instead, and later
>> wrap it into the required class.
>>
>> Our InputPort.put and emitControl method would look something like the
>> following where we handle the wrapping and unwrapping internally.
>>
>> public void put(T tuple)
>> {
>>    if (tuple instanceof CustomWrapper) {
>>      processControl(tuple.unWrap());
>>    }  else {
>>      process(tuple)
>>    }
>> }
>>
>> emitControl(Object tuple)
>> {
>>    sink.put(CustomWrapper.wrap(tuple));
>> }
>>
>> Regarding the compatibility issue, I think we have two ways of doing it:
>>
>>     1. Extend DefaultInputPort and DefaultOutputPort and create
>>     ControlAwareInput and ControlAwareOutput out of it. This might
>> require us
>>     to additionally handle specific cases when non-compatible ports
>>     (ControlAwareOutput and DefaultInput, for example) are connected to
>> each
>>     other in user apps.
>>     2. Add the additional methods in the existing Default implementations.
>>
>>
>> IMO, both of these would help in early error detection.
>>
>> ~ Bhupesh
>>
>>
>>
>>
>> On Wed, Dec 21, 2016 at 1:36 AM, Vlad Rozov <v.rozov@datatorrent.com>
>> wrote:
>>
>> A wrapper class is required for the control tuples delivery, but
>>> Port/Operator API should use Control Tuple payload object only.
>>> Implementation of the wrapper class may change from version to version,
>>> but
>>> API should not be affected by the change.
>>>
>>> I guess, assumption is that default input and output port will be
>>> extended
>>> to provide support for the control tuples. This may cause some backward
>>> compatibility issues. Consider scenario when a newer version of Malhar
>>> that
>>> relies on EOF control tuple is deployed into older version of core that
>>> does not support control tuples. In such scenario, error will be raised
>>> only when an operator tries to emit EOF control tuple at the end of a
>>> job.
>>> Introducing control tuple aware ports solve the early error detection. It
>>> will require some operators to be modified to use control tuple aware
>>> ports, but such change may help to distinguish control tuple aware
>>> operators from their old versions.
>>>
>>> Vlad
>>>
>>> On 12/20/16 04:09, Bhupesh Chawda wrote:
>>>
>>> I investigated this and seems like it is better to have a wrapper class
>>>> for
>>>> the user object.
>>>> This would serve 2 purposes:
>>>>
>>>>      1. Allow us to distinguish a custom control tuple from other
>>>> payload
>>>>      tuples.
>>>>      2. For the same control tuple received from different upstream
>>>>
>>>>      partitions, we would have some mechanism to distinguish between the
>>>> two in
>>>>      order to identify duplicates.
>>>>
>>>> Additionally, the wrapper class needs to be part of the API as
>>>> DefaultOutputPort needs to know about it, before putting it into the
>>>> sink.
>>>> We can make sure that the user is not able to extend or modify this
>>>> class
>>>> in any manner.
>>>>
>>>> ~ Bhupesh
>>>>
>>>> On Mon, Dec 19, 2016 at 12:18 PM, David Yan <davidyan@gmail.com> wrote:
>>>>
>>>> This C type parameter is going to fix the control tuple type at compile
>>>>
>>>>> time and this is actually not what we want. Note that the operator may
>>>>> receive or emit multiple different control tuple types.
>>>>>
>>>>> David
>>>>>
>>>>> On Dec 17, 2016 3:33 AM, "Tushar Gosavi" <tushar@datatorrent.com>
>>>>> wrote:
>>>>>
>>>>> We do not need to create an interface for data emitted through
>>>>> emitControl or processed through processControl. Internally we could
>>>>> wrap the user object in ControlTuple. you can add type parameter for
>>>>> control tuple object on ports.
>>>>>
>>>>> DefaultInputPort<D,C>
>>>>> D is the data type and C is the control tuple type for better error
>>>>> catching at compile phase.
>>>>>
>>>>>
>>>>> - Tushar.
>>>>>
>>>>>
>>>>> On Sat, Dec 17, 2016 at 8:35 AM, Bhupesh Chawda <
>>>>> bhupesh@datatorrent.com
>>>>> wrote:
>>>>>
>>>>> Agreed Vlad and David.
>>>>>> I am just suggesting there should be a wrapper for the user object.
It
>>>>>>
>>>>>> can
>>>>>
>>>>> be a marker interface and we can call it something else like
>>>>>> "CustomControl".
>>>>>>
>>>>>> The user object will be wrapped in another class "ControlTuple" which
>>>>>> traverses the BufferServer and will perhaps be extended from the
>>>>>> packet/Tuple class. This class will not be exposed to the user.
>>>>>>
>>>>>> ~ Bhupesh
>>>>>>
>>>>>>
>>>>>> On Sat, Dec 17, 2016 at 4:11 AM, Vlad Rozov <v.rozov@datatorrent.com>
>>>>>>
>>>>>> wrote:
>>>>>
>>>>> I agree with David. Payload of the control tuple is in the userObject
>>>>>> and
>>>>>> operators/ports don't need to be exposed to the implementation of
the
>>>>>>
>>>>>>> ControlTuple class. With the proposed interface operators developers
>>>>>>> are
>>>>>>> free to extend ControlTuple further and I don't think that such
>>>>>>>
>>>>>>> capability
>>>>>> needs to be provided. The wrapping in the ControlTuple class is
>>>>>> necessary
>>>>>> and most likely ControlTuple needs to be extended from the buffer
>>>>>> server
>>>>>>
>>>>>>> Tuple. It may be good to have a common parent other than Object
for
>>>>>>> all
>>>>>>> user payloads, but it may be a marker interface as well.
>>>>>>>
>>>>>>> Thank you,
>>>>>>>
>>>>>>> Vlad
>>>>>>>
>>>>>>>
>>>>>>> On 12/16/16 09:59, Bhupesh Chawda wrote:
>>>>>>>
>>>>>>> Hi David,
>>>>>>>
>>>>>>>> Actually, I was thinking of another API class called ControlTuple,
>>>>>>>> different from the actual tuple class in buffer server or
stram.
>>>>>>>> This could serve as a way for the Buffer server publisher
to
>>>>>>>> understand
>>>>>>>> that it is a control tuple and needs to be wrapped differently.
>>>>>>>>
>>>>>>>> ~ Bhupesh
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Dec 16, 2016 22:28, "David Yan" <davidyan@gmail.com>
wrote:
>>>>>>>>
>>>>>>>>     // DefaultInputPort
>>>>>>>>      public void processControl(ControlTuple tuple)
>>>>>>>>      {
>>>>>>>>        // Default Implementation to avoid need to implement
it in
>>>>>>>> all
>>>>>>>> implementations
>>>>>>>>      }
>>>>>>>> {code}
>>>>>>>>
>>>>>>>> {code}
>>>>>>>>     // DefaultOutputPort
>>>>>>>>      public void emitControl(ControlTuple tuple)
>>>>>>>>      {
>>>>>>>>      }
>>>>>>>>
>>>>>>>> I think we don't need to expose the ControlTuple class to
the
>>>>>>>> operator
>>>>>>>> developers because the window ID is just the current window
ID when
>>>>>>>>
>>>>>>>> these
>>>>>>>
>>>>>> methods are called. How about making them just Object? We also need
to
>>>>>>
>>>>>>> provide the way for the user to specify custom serializer for
the
>>>>>>>>
>>>>>>>> control
>>>>>>>
>>>>>> tuple.
>>>>>>
>>>>>>> David
>>>>>>>>
>>>>>>>>
>>>>>>>> On Thu, Dec 15, 2016 at 12:43 AM, Bhupesh Chawda <
>>>>>>>>
>>>>>>>> bhupesh@datatorrent.com
>>>>>>>
>>>>>> wrote:
>>>>>>
>>>>>>> Hi All,
>>>>>>>>
>>>>>>>> Here are the initial interfaces:
>>>>>>>>>
>>>>>>>>> {code}
>>>>>>>>>     // DefaultInputPort
>>>>>>>>>      public void processControl(ControlTuple tuple)
>>>>>>>>>      {
>>>>>>>>>        // Default Implementation to avoid need to implement
it in
>>>>>>>>> all
>>>>>>>>> implementations
>>>>>>>>>      }
>>>>>>>>> {code}
>>>>>>>>>
>>>>>>>>> {code}
>>>>>>>>>     // DefaultOutputPort
>>>>>>>>>      public void emitControl(ControlTuple tuple)
>>>>>>>>>      {
>>>>>>>>>      }
>>>>>>>>> {code}
>>>>>>>>>
>>>>>>>>> We have an option to add these methods to the interfaces
-
>>>>>>>>> InputPort
>>>>>>>>>
>>>>>>>>> and
>>>>>>>>
>>>>>>> OutputPort; But these would not be backward compatible and also
not
>>>>>>
>>>>>>> consistent with the current implementation of basic data tuple
flow
>>>>>>>>>
>>>>>>>>> (as
>>>>>>>>
>>>>>>> with process() and emit()).
>>>>>>
>>>>>>> We also need to expose an interface / class for users to wrap
their
>>>>>>>>> object
>>>>>>>>> and emit downstream. This should be part of API.
>>>>>>>>>
>>>>>>>>> {code}
>>>>>>>>> public class ControlTuple extends Tuple
>>>>>>>>> {
>>>>>>>>>      Object userObject;
>>>>>>>>>
>>>>>>>>>      public ControlTuple(long windowId, Object userObject)
>>>>>>>>>      {
>>>>>>>>>        //
>>>>>>>>>      }
>>>>>>>>> }
>>>>>>>>> {code}
>>>>>>>>>
>>>>>>>>> The emitted tuples would traverse the same flow as with
other
>>>>>>>>> control
>>>>>>>>> tuples. The plan is to intercept the control tuples in
GenericNode
>>>>>>>>> and
>>>>>>>>> use
>>>>>>>>> the Reservior to emit the control tuples at the end of
the window.
>>>>>>>>>
>>>>>>>>> GenericNode seems to be the best place to buffer incoming
custom
>>>>>>>>>
>>>>>>>>> control
>>>>>>>>
>>>>>>> tuples without delivering them immediately to the operator port.
Once
>>>>>>
>>>>>>> the
>>>>>>>>
>>>>>>> end of the window is reached, we plan to use the reservoir sink
to
>>>>>>
>>>>>>> push
>>>>>>>>
>>>>>>> them to the port. This is different behavior than any other control
>>>>>>
>>>>>>> tuple
>>>>>>>>
>>>>>>> where we are changing the order of tuples in the stream. The
custom
>>>>>>
>>>>>>> control
>>>>>>>>>
>>>>>>>> tuples will be buffered and not delivered to the ports until
the end
>>>>>>>> of
>>>>>>>>
>>>>>>> the
>>>>>>
>>>>>>> window.
>>>>>>>>
>>>>>>>>> To accomplish this, we need to have a public method in
>>>>>>>>>
>>>>>>>>> SweepableReservoir
>>>>>>>>
>>>>>>> which allows to put a tuple back in the sink of the reservoir.
>>>>>>
>>>>>>> ~ Bhupesh
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>

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