Custom control tuples are control tuples emitted by an operator itself
and not by the platform. Prior to the introduction of the custom control
tuples, only Apex engine itself puts control tuples into various sinks,
so the engine created necessary Tuple objects with the corresponding
type prior to calling Sink.put().
Not all sinks need to be changed. Only control tuple aware sinks should
provide such functionality. In the case there is a lot of code
duplication, please create an abstract class, that other control aware
sinks will extend from.
Thank you,
Vlad
On 12/23/16 06:24, Bhupesh Chawda wrote:
Hi Vlad,
Thanks for the pointer on delegating the wrapping of the user tuple to the
control port. I was trying this out today.
The problem I see us if we introduce a putControlTuple() method in Sink,
then a lot of the existing sinks would change. Also the changes seemed
redundant as, the existing control tuples already use the put() method of
sinks. So why do something special for custom control tuples?
The only aspect in which the custom control tuples are different is that
these will be generated by the user and will actually be delivered to the
ports in a different order. Perhaps we should be able to use the existing
flow. The only problems as outlined before seem to be identification of the
user tuple as a control tuple.
~ Bhupesh
On Thu, Dec 22, 2016 at 10:44 PM, Vlad Rozov <v.ro...@datatorrent.com>
wrote:
Why is it necessary to wrap in the OutputPort? Can't it be delegated to a
Sink by introducing new putControlTuple method?
Thank you,
Vlad
On 12/21/16 22:10, Bhupesh Chawda wrote:
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.ro...@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.ro...@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 <david...@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" <tus...@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 <
bhup...@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.ro...@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" <david...@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 <
bhup...@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
