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From Ravikumar Hawaldar <ravikumar.hawal...@gmail.com>
Subject Re: How to maintain the state of a variable in a map transformation.
Date Thu, 09 Jun 2016 13:01:25 GMT
Hi Fabian, Thank you for your answers,

1) If there is only single instance of that function, then it will defeat
the purpose of distributed correct me if I am wrong, so If I run
parallelism with 1 on cluster does that mean it will execute on only one

2) I mean to say, when a map operator returns a variable, is there any
other function which takes that updated variable and returns that to all
instances of map?

3) Question Cleared.

4) My question was can I use same ExecutionEnvironment for all flink
programs in a module.

5) Question Cleared.


On 9 June 2016 at 17:58, Fabian Hueske <fhueske@gmail.com> wrote:

> Hi Ravikumar,
> I'll try to answer your questions:
> 1) If you set the parallelism of a map function to 1, there will be only a
> single instance of that function regardless whether it is execution locally
> or remotely in a cluster.
> 2) Flink does also support aggregations, (reduce, groupReduce, combine,
> ...). However, I do not see how this would help with a stateful map
> function.
> 3) In Flink DataSet programs you usually construct the complete program
> and call execute() after you have defined your sinks. There are two
> exceptions: print() and collect() which both add special sinks and
> immediately execute your program. print() prints the result to the stdout
> of the submitting client and collect() fetches a dataset as collection.
> 4) I am not sure I understood your question. When you obtain an
> ExecutionEnvironment with ExecutionEnvironment.getExecutionEnvrionment()
> the type of the returned environment depends on the context in which the
> program was executed. It can be a local environment if it is executed from
> within an IDE or a RemodeExecutionEnvironment if the program is executed
> via the CLI client and shipped to a remote cluster.
> 5) A map operator processes records one after the other, i.e., as a
> sequence. If you need a certain order, you can call DataSet.sortPartition()
> to locally sort the partition.
> Hope that helps,
> Fabian
> 2016-06-09 12:23 GMT+02:00 Ravikumar Hawaldar <
> ravikumar.hawaldar@gmail.com>:
>> Hi Till, Thank you for your answer, I have couple of questions
>> 1) Setting parallelism on a single map function in local is fine but on
>> distributed will it work as local execution?
>> 2) Is there any other way apart from setting parallelism? Like spark
>> aggregate function?
>> 3) Is it necessary that after transformations to call execute function?
>> Or Execution starts as soon as it encounters a action (Similar to Spark)?
>> 4) Can I create a global execution environment (Either local or
>> distributed) for different Flink program in a module?
>> 5) How to make the records come in sequence for a map or any other
>> operator?
>> Regards,
>> Ravikumar
>> On 8 June 2016 at 21:14, Till Rohrmann <trohrmann@apache.org> wrote:
>>> Hi Ravikumar,
>>> Flink's operators are stateful. So you can simply create a variable in
>>> your mapper to keep the state around. But every mapper instance will have
>>> it's own state. This state is determined by the records which are sent to
>>> this mapper instance. If you need a global state, then you have to set the
>>> parallelism to 1.
>>> Cheers,
>>> Till
>>> On Wed, Jun 8, 2016 at 5:08 PM, Ravikumar Hawaldar <
>>> ravikumar.hawaldar@gmail.com> wrote:
>>>> Hello,
>>>> I have an DataSet<UserDefinedType> which is roughly a record in a
>>>> DataSet Or a file.
>>>> Now I am using map transformation on this DataSet to compute a variable
>>>> (coefficients of linear regression parameters and data structure used is
>>>> double[]).
>>>> Now the issue is that, per record the variable will get updated and I
>>>> am struggling to maintain state of this variable for the next record.
>>>> In simple, for first record the variable values will be 0.0, and after
>>>> first record the variable will get updated and I have to pass this updated
>>>> variable for the second record and so on for all records in DataSet.
>>>> Any suggestions on how to maintain state of a variable?
>>>> Regards,
>>>> Ravikumar

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