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From Tony Wei <tony19920...@gmail.com>
Subject Re: dynamically partitioned stream
Date Thu, 07 Sep 2017 08:24:16 GMT
Hi Martin,

What I was talking is about how to store the arguments' state. In the
example you explained your use case to Aljoscha.

4          f1(V4, V3, V3)
            f2(V4, V3)
3          f1(V3, V3, V3)
2          -
1          -

You showed that when lambda f2 came, it would emit f2(V4, V3) immediately.
However, the second argument (B, V3, 3) came before f2. You couldn't know
how to route it at that time.

If you didn't store this data's state, then f2(V4, V3) won't happen and the
problem is easily.
Otherwise, you had to route all data and all lambda to the same node to
guarantee that every lambda won't lose any  their arguments' state.

Best,
Tony Wei

2017-09-07 14:31 GMT+08:00 Martin Eden <martineden131@gmail.com>:

> Hi Tony,
>
> Yes exactly I am assuming the lambda emits a value only after it has been
> published to the control topic (t1) and at least 1 value arrives in the
> data topic for each of it's arguments. This will happen at a time t2 > t1.
> So yes, there is uncertainty with regards to when t2 will happen. Ideally
> t2 - t1 ~ 0 but for our use case it is fine. Is this the correctness that
> you are talking about? Do I have the right picture of what happens?
>
> Thanks
> M
>
> On Thu, Sep 7, 2017 at 3:11 AM, Tony Wei <tony19920430@gmail.com> wrote:
>
>> Hi Martin,
>>
>> The performance is an issue, but in your case, yes, it might not be a
>> problem if X << N.
>>
>> However, the other problem is where data should go in the beginning if
>> there is no lambda been received. This problem doesn't associate with
>> performance, but instead with correctness. If you want to keep the value
>> state for the incoming lambda you should broadcast it to all nodes, because
>> you would never know where the next lambda that requires this data would be
>> routed to. Of course, you can send this data to a pre-defined node and
>> route the lambda to this node, but this will lead to all data in the same
>> node to let all lambda can get all required data. It is not a good solution
>> because of a lack of scalability.
>>
>> In my origin thought, it is based on only storing state of data after you
>> receive at least one lambda that requires it, so that data has its
>> destination node to go. Can this assumption be acceptable in your case?
>> What do you think?
>>
>> Best,
>> Tony Wei
>>
>> 2017-09-06 22:41 GMT+08:00 Martin Eden <martineden131@gmail.com>:
>>
>>> Hi Aljoscha, Tony,
>>>
>>> We actually do not need all the keys to be on all nodes where lambdas
>>> are. We just need the keys that represent the data for the lambda arguments
>>> to be routed to the same node as the lambda, whichever one it might be.
>>>
>>> Essentially in the solution we emit the data multiple times and by doing
>>> that we roughly multiply the input rate by the average number of lambdas a
>>> key is a part of (X). In terms of memory this is O(X * N) where N is the
>>> number of keys int the data. N is the large bit. If X ~ N then we have O
>>> (N^2) complexity for the Flink state. And in that case yes I see your point
>>> about performance Aljoscha. But if X << N, as is our case, then we have
>>> O(N) which should be manageable by Flink's distributed state mechanism
>>> right? Do you see any gotchas in this new light? Are my assumptions correct?
>>>
>>> Thanks,
>>> M
>>>
>>>
>>>
>>>
>>>
>>> On Sat, Sep 2, 2017 at 3:38 AM, Tony Wei <tony19920430@gmail.com> wrote:
>>>
>>>> Hi Martin, Aljoscha
>>>>
>>>> I think Aljoscha is right. My origin thought was to keep the state
>>>> only after a lambda function coming.
>>>>
>>>> Use Aljoscha's scenario as example, initially, all data will be
>>>> discarded because there is no any lambdas. When lambda f1 [D, E] and
>>>> f2 [A, C] comes, A, C begin to be routed to machine "0" and D, E begin to
>>>> be routed to machine "1". Then, when we get a new lambda f3 [C, D], we
>>>> can duplicate C, D and route these copies to machine "2".
>>>>
>>>> However, after reading your example again, I found what you want is a
>>>> whole picture for all variables' state in a global view, so that no matter
>>>> what time a new lambda comes it can always get its variables' state
>>>> immediately. In that case, I have the same opinion as Aljoscha.
>>>>
>>>> Best,
>>>> Tony Wei
>>>>
>>>> 2017-09-01 23:59 GMT+08:00 Aljoscha Krettek <aljoscha@apache.org>:
>>>>
>>>>> Hi Martin,
>>>>>
>>>>> I think with those requirements this is very hard (or maybe
>>>>> impossible) to do efficiently in a distributed setting. It might be that
>>>>> I'm misunderstanding things but let's look at an example. Assume that
>>>>> initially, we don't have any lambdas, so data can be sent to any machine
>>>>> because it doesn't matter where they go. Now, we get a new lambda f2
[A,
>>>>> C]. Say this gets routed to machine "0", now this means that messages
with
>>>>> key A and C also need to be router to machine "0". Now, we get a new
lambda
>>>>> f1 [D, E], say this gets routed to machine "2", meaning that messages
with
>>>>> key D and E are also routed to machine "2".
>>>>>
>>>>> Then, we get a new lambda f3 [C, D]. Do we now re-route all previous
>>>>> lambdas and inputs to different machines? They all have to go to the
same
>>>>> machine, but which one? I'm currently thinking that there would need
to be
>>>>> some component that does the routing, but this has to be global, so it's
>>>>> hard to do in a distributed setting.
>>>>>
>>>>> What do you think?
>>>>>
>>>>> Best,
>>>>> Aljoscha
>>>>>
>>>>> On 1. Sep 2017, at 07:17, Martin Eden <martineden131@gmail.com>
wrote:
>>>>>
>>>>> This might be a way forward but since side inputs are not there I will
>>>>> try and key the control stream by the keys in the first co flat map.
>>>>>
>>>>> I'll see how it goes.
>>>>>
>>>>> Thanks guys,
>>>>> M
>>>>>
>>>>> On Thu, Aug 31, 2017 at 5:16 PM, Tony Wei <tony19920430@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Hi Martin,
>>>>>>
>>>>>> Yes, that is exactly what I thought.
>>>>>> But the first step also needs to be fulfilled  by SideInput. I'm
not
>>>>>> sure how to achieve this in the current release.
>>>>>>
>>>>>> Best,
>>>>>> Tony Wei
>>>>>>
>>>>>> Martin Eden <martineden131@gmail.com>於 2017年8月31日 週四,下午11:32寫道:
>>>>>>
>>>>>>> Hi Aljoscha, Tony,
>>>>>>>
>>>>>>> Aljoscha:
>>>>>>> Yes it's the first option you mentioned.
>>>>>>> Yes, the stream has multiple values in flight for A, B, C. f1
needs
>>>>>>> to be applied each time a new value for either A, B or C comes
in. So we
>>>>>>> need to use state to cache the latest values. So using the example
data
>>>>>>> stream in my first msg the emitted stream should be:
>>>>>>>
>>>>>>> 1. Data Stream:
>>>>>>> KEY VALUE TIME
>>>>>>> .
>>>>>>> .
>>>>>>> .
>>>>>>> C      V6        6
>>>>>>> B      V6        6
>>>>>>> A      V5        5
>>>>>>> A      V4        4
>>>>>>> C      V3        3
>>>>>>> A      V3        3
>>>>>>> B      V3        3
>>>>>>> B      V2        2
>>>>>>> A      V1        1
>>>>>>>
>>>>>>> 2. Control Stream:
>>>>>>> Lambda  ArgumentKeys TIME
>>>>>>> .
>>>>>>> .
>>>>>>> .
>>>>>>> f2            [A, C]                 4
>>>>>>> f1            [A, B, C]            1
>>>>>>>
>>>>>>> 3. Expected emitted stream:
>>>>>>> TIME    VALUE
>>>>>>> .
>>>>>>> .
>>>>>>> .
>>>>>>> 6          f1(V5, V6, V3)
>>>>>>>             f1(V5, V6, V6)
>>>>>>>             f2(V5, V6)
>>>>>>> 5          f1(V5, V3, V3)
>>>>>>>             f2(V5, V3)
>>>>>>> 4          f1(V4, V3, V3)
>>>>>>>             f2(V4, V3)
>>>>>>> 3          f1(V3, V3, V3)
>>>>>>> 2          -
>>>>>>> 1          -
>>>>>>>
>>>>>>> So essentially as soon as the argument list fills up then we
apply
>>>>>>> the function/lambda at each new arriving message in the data
stream for
>>>>>>> either argument key.
>>>>>>>
>>>>>>> Tony:
>>>>>>> Yes we need to group by and pass to the lambda.
>>>>>>> Ok, so what you are proposing might work. So your solution assumes
>>>>>>> that we have to connect with the control stream twice? Once for
the tagging
>>>>>>> and another time re-connect-ing the control stream with the tagged
stream
>>>>>>> for the actual application of the function/lambda?
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Alex
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Aug 31, 2017 at 2:57 PM, Aljoscha Krettek <
>>>>>>> aljoscha@apache.org> wrote:
>>>>>>>
>>>>>>>> Hi Martin,
>>>>>>>>
>>>>>>>> In your original example, what does this syntax mean exactly:
>>>>>>>>
>>>>>>>> f1            [A, B, C]            1
>>>>>>>>
>>>>>>>> Does it mean that f1 needs one A, one B and one C from the
main
>>>>>>>> stream? If yes, which ones, because there are multiple As
and Bs and so on.
>>>>>>>> Or does it mean that f1 can apply to an A or a B or a C?
If it's the first,
>>>>>>>> then I think it's quite hard to find a partitioning such
that both f1, f2,
>>>>>>>> and all A, B, and C go to the same machine.
>>>>>>>>
>>>>>>>> Best,
>>>>>>>> Aljoscha
>>>>>>>>
>>>>>>>> On 31. Aug 2017, at 15:53, Tony Wei <tony19920430@gmail.com>
wrote:
>>>>>>>>
>>>>>>>> Hi Martin,
>>>>>>>>
>>>>>>>> So the problem is that you want to group those arguments
in Data
>>>>>>>> Stream and pass them to the lambda function from Control
Stream at the same
>>>>>>>> time. Am I right?
>>>>>>>>
>>>>>>>> If right, then you could give each lambda function an id
as well.
>>>>>>>> Use these ids to tag those arguments to which they belong.
>>>>>>>> After that, keyBy function could be used to group those arguments
>>>>>>>> belonging to the same lambda function. Joining this stream
with Control
>>>>>>>> Stream by function id could make arguments and function be
in the same
>>>>>>>> instance.
>>>>>>>>
>>>>>>>> What do you think? Could this solution solve your problem?
>>>>>>>>
>>>>>>>> Best,
>>>>>>>> Tony Wei
>>>>>>>>
>>>>>>>> 2017-08-31 20:43 GMT+08:00 Martin Eden <martineden131@gmail.com>:
>>>>>>>>
>>>>>>>>> Thanks for your reply Tony,
>>>>>>>>>
>>>>>>>>> Yes we are in the latter case, where the functions/lambdas
come in
>>>>>>>>> the control stream. Think of them as strings containing
the logic of the
>>>>>>>>> function. The values for each of the arguments to the
function come from
>>>>>>>>> the data stream. That is why we need to co-locate the
data stream messages
>>>>>>>>> for the corresponding keys with the control message that
has the function
>>>>>>>>> to be applied.
>>>>>>>>>
>>>>>>>>> We have a way of interpreting the logic described in
the string
>>>>>>>>> and executing it on the incoming values from the data
stream. This is
>>>>>>>>> kicked off from within the Flink runtime (synchronous
to a flatMap of the
>>>>>>>>> RichCoFlatMapFunction) but is not using Flink predefined
>>>>>>>>> operators or functions.
>>>>>>>>>
>>>>>>>>> So yeah I see your point about mapping the arguments
but the
>>>>>>>>> problem is not really that, the problem is making sure
that the values in
>>>>>>>>> the control stream are in the same instance of the task/
keyed managed
>>>>>>>>> state as a the actual control stream message. Once they
are we can pass
>>>>>>>>> them in.
>>>>>>>>>
>>>>>>>>> Any other thoughts?
>>>>>>>>>
>>>>>>>>> M
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Thu, Aug 31, 2017 at 12:06 PM, Tony Wei <tony19920430@gmail.com
>>>>>>>>> > wrote:
>>>>>>>>>
>>>>>>>>>> Hi Martin,
>>>>>>>>>>
>>>>>>>>>> About problem 2. How were those lambda functions
created?
>>>>>>>>>> Pre-defined functions / operators or automatically
generated based on the
>>>>>>>>>> message from Control Stream?
>>>>>>>>>>
>>>>>>>>>> For the former, you could give each function one
id and user
>>>>>>>>>> flapMap to duplicate data with multiple ids. Then,
you could use filter
>>>>>>>>>> function and send them to the corresponding operators.
>>>>>>>>>>
>>>>>>>>>> For the general case like the latter, because you
had broadcasted
>>>>>>>>>> the messages to all tasks, it could always build
a mapping table from
>>>>>>>>>> argument keys to lambda functions in each sub-task
and use the map to
>>>>>>>>>> process the data. But I was wondering if it is possible
to generate a
>>>>>>>>>> completely new function in the runtime.
>>>>>>>>>>
>>>>>>>>>> Best,
>>>>>>>>>> Tony Wei
>>>>>>>>>>
>>>>>>>>>> 2017-08-31 18:33 GMT+08:00 Martin Eden <martineden131@gmail.com>:
>>>>>>>>>>
>>>>>>>>>>> Thanks for your reply Tony.
>>>>>>>>>>>
>>>>>>>>>>> So there are actually 2 problems to solve:
>>>>>>>>>>>
>>>>>>>>>>> 1. All control stream msgs need to be broadcasted
to all tasks.
>>>>>>>>>>>
>>>>>>>>>>> 2. The data stream messages with the same keys
as those
>>>>>>>>>>> specified in the control message need to go to
the same task as well, so
>>>>>>>>>>> that all the values required for the lambda (i.e.
functions f1, f2 ...) are
>>>>>>>>>>> there.
>>>>>>>>>>>
>>>>>>>>>>> In my understanding side inputs (which are actually
not
>>>>>>>>>>> available in the current release) would address
problem 1.
>>>>>>>>>>>
>>>>>>>>>>> To address problem 1 I also tried dataStream.keyBy(key).connect(
>>>>>>>>>>> controlStream.broadcast).flatMap(new RichCoFlatMapFunction)
but
>>>>>>>>>>> I get a runtime exception telling me I still
need to do a keyBy before the
>>>>>>>>>>> flatMap. So are the upcoming side inputs the
only way to broadcast a
>>>>>>>>>>> control stream to all tasks of a coFlatMap? Or
is there another way?
>>>>>>>>>>>
>>>>>>>>>>> As for problem 2, I am still pending a reply.
Would appreciate
>>>>>>>>>>> if anyone has some suggestions.
>>>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>> M
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Thu, Aug 31, 2017 at 9:59 AM, Tony Wei <
>>>>>>>>>>> tony19920430@gmail.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Hi Martin,
>>>>>>>>>>>>
>>>>>>>>>>>> Let me understand your question first.
>>>>>>>>>>>> You have two Stream: Data Stream and Control
Stream and you
>>>>>>>>>>>> want to select data in Data Stream based
on the key set got from Control
>>>>>>>>>>>> Stream.
>>>>>>>>>>>>
>>>>>>>>>>>> If I were not misunderstanding your question,
I think SideInput
>>>>>>>>>>>> is what you want.
>>>>>>>>>>>> https://cwiki.apache.org/confluence/display/FLINK/FLIP-17+Si
>>>>>>>>>>>> de+Inputs+for+DataStream+API#FLIP-17SideInputsforDataStreamA
>>>>>>>>>>>> PI-StoringSide-InputData
>>>>>>>>>>>> It lets you to define one stream as a SideInput
and can be
>>>>>>>>>>>> assigned to the other stream, then the data
in SideInput stream will be
>>>>>>>>>>>> broadcasted.
>>>>>>>>>>>>
>>>>>>>>>>>> So far, I have no idea if there is any solution
to solve this
>>>>>>>>>>>> without SideInput.
>>>>>>>>>>>>
>>>>>>>>>>>> Best,
>>>>>>>>>>>> Tony Wei
>>>>>>>>>>>>
>>>>>>>>>>>> 2017-08-31 16:10 GMT+08:00 Martin Eden <martineden131@gmail.com
>>>>>>>>>>>> >:
>>>>>>>>>>>>
>>>>>>>>>>>>> Hi all,
>>>>>>>>>>>>>
>>>>>>>>>>>>> I am trying to implement the following
using Flink:
>>>>>>>>>>>>>
>>>>>>>>>>>>> I have 2 input message streams:
>>>>>>>>>>>>>
>>>>>>>>>>>>> 1. Data Stream:
>>>>>>>>>>>>> KEY VALUE TIME
>>>>>>>>>>>>> .
>>>>>>>>>>>>> .
>>>>>>>>>>>>> .
>>>>>>>>>>>>> C      V6        6
>>>>>>>>>>>>> B      V6        6
>>>>>>>>>>>>> A      V5        5
>>>>>>>>>>>>> A      V4        4
>>>>>>>>>>>>> C      V3        3
>>>>>>>>>>>>> A      V3        3
>>>>>>>>>>>>> B      V3        3
>>>>>>>>>>>>> B      V2        2
>>>>>>>>>>>>> A      V1        1
>>>>>>>>>>>>>
>>>>>>>>>>>>> 2. Control Stream:
>>>>>>>>>>>>> Lambda  ArgumentKeys TIME
>>>>>>>>>>>>> .
>>>>>>>>>>>>> .
>>>>>>>>>>>>> .
>>>>>>>>>>>>> f2            [A, C]                
4
>>>>>>>>>>>>> f1            [A, B, C]            1
>>>>>>>>>>>>>
>>>>>>>>>>>>> I want to apply the lambdas coming in
the control stream to
>>>>>>>>>>>>> the selection of keys that are coming
in the data stream.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Since we have 2 streams I naturally thought
of connecting them
>>>>>>>>>>>>> using .connect. For this I need to key
both of them by a certain criteria.
>>>>>>>>>>>>> And here lies the problem, how can I
make sure the messages with keys A,B,C
>>>>>>>>>>>>> specified in the control stream end up
in the same task as well as the
>>>>>>>>>>>>> control message (f1, [A, B, C]) itself.
Basically I don't know how to key
>>>>>>>>>>>>> by to achieve this.
>>>>>>>>>>>>>
>>>>>>>>>>>>> I suspect a custom partitioner is required
that partitions the
>>>>>>>>>>>>> data stream based on the messages in
the control stream? Is this even
>>>>>>>>>>>>> possible?
>>>>>>>>>>>>>
>>>>>>>>>>>>> Any suggestions welcomed!
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>> M
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>
>

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