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From Till Rohrmann <trohrm...@apache.org>
Subject Re: How MapFunction gets executed?
Date Thu, 16 Jun 2016 15:49:57 GMT
Hi Yan Chou Chen,

Flink does not instantiate for each record a mapper. Instead, it will
create as many mappers as you've defined with the parallelism. Each of
these mappers is deployed to a slot on a TaskManager. When it is deployed
and before it receives records, the open method is called once. Then
incoming records are processed as they arrive at the operator. Once the
operator has finished processing (in the streaming case, this means that
the user has stopped or cancelled the job) it will call the close method.
The close method should also be called if your job fails. Therefore, I
cannot explain why some of your resources don't get closed. Could you check
whether the logs contains something suspicious.

Cheers,
Till

On Thu, Jun 16, 2016 at 5:07 PM, Yan Chou Chen <ycchen915@gmail.com> wrote:

> A quick question. When running a stream job that executes
> DataStream.map(MapFunction) , after data is read from Kafka, does each
> MapFunction is created per item or based on parallelism?
>
> For instance, for the following code snippet
>
> val env = StreamExecutionEnvironment.getExeutionEnvironment
> val stream = env.addSource(FlinkKafkaConsumer09(...))
> stream.map(new RichMapFunction[String, Unit] {
>
>     // my AsyncHttpClient instance
>
>     override def open(params: Configuration) { /* create my
> AsyncHttpClient instance, etc. */ }
>
>     override def close() { /* close my AsyncHttpClient instance*/ }
>
>     override def map(record: String) {
>         // my code
>     }
> })
>
> Is RichMapFunction created for each record (as String in the above
> example)? Or say the program set parallelism to 4 so 4 RichMapFunction
> instances are created first, then data read from Kafka consumer is
> divided into 4 partitions (or something similar), and then map(record:
> String) is called within something like while loop? Or what is the
> actual flow? Or source code I can start from (I trace through
> StreamExecutionEnvironment/ addSource/ DataStream/ transform/
> addOperator etc., but I then get lost in source code)?
>
> Basically my problem is I have an AsyncHttpClient instance opened
> within open() function and close in close function according to the
> RichMapFunction doc. However, an issue is that in some cases my
> AsyncHttpClient instance is not executed which displays warning like
>
> AsyncHttpClient.close() hasn't been invoked, which may produce file
> descriptor leaks
>
> Therefore I would like to know the life cycle so that I can close
> resource appropriately.
>
> Thanks
>

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