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From "Matthias J. Sax" <mj...@apache.org>
Subject Re: How to force the parallelism on small streams?
Date Wed, 02 Sep 2015 15:56:15 GMT

If I understand you correctly, you want to have 100 mappers. Thus you
need to apply the .setParallelism() after .map()

> addSource(myFileSource).rebalance().map(myFileMapper).setParallelism(100)

The order of commands you used, set the dop for the source to 100 (which
might be ignored, if the provided source function "myFileSource" does
not implements "ParallelSourceFunction" interface). The dop for the
mapper should be the default value.

Using .rebalance() is absolutely correct. It distributes the emitted
tuples in a round robin fashion to all consumer tasks.


On 09/02/2015 05:41 PM, LINZ, Arnaud wrote:
> Hi,
> I have a source that provides few items since it gives file names to the
> mappers. The mapper opens the file and process records. As the files are
> huge, one input line (a filename) gives a consequent work to the next stage.
> My topology looks like :
> addSource(myFileSource).rebalance().setParallelism(100).map(myFileMapper)
> If 100 mappers are created, about 85 end immediately and only a few
> process the files (for hours). I suspect an optimization making that
> there is a minimum number of lines to pass to the next node or it is
> “shutdown” ; but in my case I do want the lines to be evenly distributed
> to each mapper.
> How to enforce that ?
> Greetings,
> Arnaud
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