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Subject: Re: Best way to deriving streams from another one
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From: Chesnay Schepler <chesnay@apache.org>
Message-ID: <9fe0ed98-7457-49ff-c026-6ce03914781e@apache.org>
Date: Mon, 11 Sep 2017 19:32:36 +0200
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archived-at: Mon, 11 Sep 2017 17:32:43 -0000

Have a look at side outputs in the documentation, they allow you to emit 
to multiple streams (of different types!) with a ProcessFunction.

On 10.09.2017 22:15, AndreaKinn wrote:
> Hi,
> I have a data stream resulting from an operation executed on a data stream
> of data.
> Essentially I want to obtain two different streams from that one to send
> their to different cassandra tables.
>
> I.e.:
>
> datastream 0 composed by Tuple3<Val1, Val2, Val3>
>
> I want to have:
>
>   a datastream 1 composed by every triple <Val1,Val2,Val3> of datastream 0
> where Val2 > X
> and
> a data stream 2 composed by every couple <Val1, Val3>.
>
> This lied me to have two datastreams with Tuples of different arity (3 and
> 2).
>
> Currently I have implemented it getting the 0 datastream and then calling
> separately a map function to retrieve datastream 2 and a flatmap function to
> retrieve datastream 1. So I have two different prepared statement of
> Cassandra called on the two different streams.
> It works fine.
>
> However this solutions looks really awful and inefficient, there is a more
> elegant alternative?
>
> I tried also to send towards Cassandra a datastream<Val1,Val2,Val3> and
> select in the statement just two values (in this way I should use just the
> flatmap operator) but during the execution raise an exception on it.
>
>
>
> --
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>