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From Ufuk Celebi <...@apache.org>
Subject Re: Merge the states of different partition in streaming
Date Wed, 28 Sep 2016 15:28:22 GMT
Great to hear!

On Wed, Sep 28, 2016 at 5:18 PM, Simone Robutti
<simone.robutti@radicalbit.io> wrote:
> Solved. Probably there was an error in the way I was testing. Also I
> simplified the job and it works now.
>
> 2016-09-27 16:01 GMT+02:00 Simone Robutti <simone.robutti@radicalbit.io>:
>>
>> Hello,
>>
>> I'm dealing with an analytical job in streaming and I don't know how to
>> write the last part.
>>
>> Actually I want to count all the elements in a window with a given status,
>> so I keep a state with a Map[Status,Long]. This state is updated starting
>> from tuples containing the oldStatus and the newStatus. So every event
>> generates a +1 for the new status and a -1 for the old status. Then I want
>> to reduce all these counts and move from a local and partial state to a
>> global state that will be written in output.
>>
>> Right now my code look like:
>>
>> filteredLatestOrders.keyBy(x =>
>> x._1.getStatus).mapWithState(updateState).keyBy(x=>"0").reduce((orderA,orderB)=>orderA.sum(orderB))
>>
>> where "filteredLatestOrder" is a DataStream containing informations about
>> the elements, the new state and the old state.
>>
>> This produces in output:
>>
>> 2> Map(DRAFT -> 0, RESERVED -> 1, PICKED -> 0, PACKED -> 0)
>> 2> Map(DRAFT -> 0, RESERVED -> 2, PICKED -> 0, PACKED -> 0)
>> 2> Map(DRAFT -> 0, RESERVED -> 3, PICKED -> 0, PACKED -> 1)
>> 3> Map(DRAFT -> 0, RESERVED -> -1, PICKED -> 1, PACKED -> 0)
>> 4> Map(DRAFT -> 0, RESERVED -> -1, PICKED -> 0, PACKED -> 1)
>>
>> I thought that keying with a fixed value would collect all the elements in
>> a single node so that I could finally compute the final result, but they are
>> left on different nodes and are never summed.
>>
>> Is this the correct approach? In that case, how can I do what I need? Is
>> there a smarter way to count distinct evolving elements by their status in a
>> streaming? Mind that the original source of events are updates to the status
>> of an element and the requirement is that I want to count only the latest
>> status available.
>>
>> Thank you in advance,
>>
>> Simone
>
>

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