Re: finite subset of an infinite data stream

Posted by rss rss on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/finite-subset-of-an-infinite-data-stream-tp3400p3410.html

Hello, 

  thanks for the answer but windows produce periodical results. I used your example but the data source is changed to TCP stream:

        DataStream<String> text = env.socketTextStream("localhost", 2015, '\n');

        DataStream<Tuple2<String, Integer>> wordCounts =

                text

                .flatMap(new LineSplitter())

                .keyBy(0)

                .timeWindow(Time.of(5, TimeUnit.SECONDS))

                .sum(1);

        wordCounts.print();

        env.execute("WordCount Example");

 I see an infinite results printing instead of the only list.

 The data source is following script:

-----------------------------------------------------

#!/usr/bin/env ruby

require 'socket'

server = TCPServer.new 2015

loop do

  Thread.start(server.accept) do |client|

    puts Time.now.to_s + ': New client!'

    loop do

      client.puts "#{Time.now} #{[*('A'..'Z')].sample(3).join}"

      sleep rand(1000)/1000.0

    end

    client.close

  end

end

-----------------------------------------------------

  My purpose is to union an infinite real time data stream with filtered persistent data where the condition of filtering is provided by external requests. And the only result of union is interested. In this case I guess I need a way to terminate the stream. May be I wrong.

  Moreover it should be possible to link the streams by next request with other filtering criteria. That is create new data transformation chain after running of env.execute("WordCount Example"). Is it possible now? If not, is it possible with minimal changes of the core of Flink?

Regards,

Roman

2015-11-09 12:34 GMT+04:00 Stephan Ewen <[hidden email]>:

Hi!

If you want to work on subsets of streams, the answer is usually to use windows, "stream.keyBy(...).timeWindow(Time.of(1, MINUTE))".

The transformations that you want to make, do they fit into a window function?

There are thoughts to introduce something like global time windows across the entire stream, inside which you can work more in a batch-style, but that is quite an extensive change to the core.

Greetings,

Stephan

On Sun, Nov 8, 2015 at 5:15 PM, rss rss <[hidden email]> wrote:

Hello,

 

I need to extract a finite subset like a data buffer from an infinite data stream. The best way for me is to obtain a finite stream with data accumulated for a 1minute before (as example). But I not found any existing technique to do it.

 

As a possible ways how to do something near to a stream’s subset I see following cases:

-          some transformation operation like ‘take_while’ that produces new stream but able to switch one to FINISHED state. Unfortunately I not found how to switch the state of a stream from a user code of transformation functions;

-          new DataStream or StreamSource constructors which allow to connect a data processing chain to the source stream. It may be something like mentioned take_while transform function or modified StreamSource.run method with data from the source stream.

 

That is I have two questions.

1)      Is there any technique to extract accumulated data from a stream as a stream (to union it with another stream)? This is like pure buffer mode.

2)      If the answer to first question is negative, is there something like take_while transformation or should I think about custom implementation of it? Is it possible to implement it without modification of the core of Flink?

 

Regards,

Roman