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From Stephan Ewen <se...@apache.org>
Subject Re: Issue with sharing state in CoFlatMapFunction
Date Tue, 17 Nov 2015 12:43:47 GMT
Is the CoFlatMapFunction intended to be executed in parallel?

If yes, you need some way to deterministically assign which record goes to
which parallel instance. In some way the CoFlatMapFunction does a parallel
(partitions) join between the model and the result of the session windows,
so you need some form of key that selects which partition the elements go
to. Does that make sense?

If not, try to set it to parallelism 1 explicitly.

Greetings,
Stephan


On Tue, Nov 17, 2015 at 1:11 PM, Vladimir Stoyak <vstoyak@yahoo.com> wrote:

> My model DataStream is not keyed and does not have any windows, only the
> main stream has windows and apply function
>
> I have two Kafka Streams, one for events and one for model
>
> DataStream<Model> model_stream
> = env.addSource(new FlinkKafkaConsumer082<Model>(model_topic, new AvroDeserializationSchema(Model.class),
properties));
>
>
> DataStream<Raw> main_stream = env.addSource(new FlinkKafkaConsumer082<Raw>(raw_topic,
new AvroDeserializationSchema(Raw.class), properties));
>
>
> My topology looks like this:
> main_stream
> .assignTimestamps(new myTimeExtractor())
> .keyBy("event_key")
> .window(GlobalWindows.create())
> .trigger(new sessionTrigger(session_timeout))
> .apply(new AggFunction())
> .connect(model_stream)
> .flatMap(new applyModel())
> .print();
>
>  AggFunction is a simple aggregate function:
> Long start_ts=Long.MAX_VALUE;
>         Long end_ts=Long.MIN_VALUE;
>         Long dwell_time=0L,last_event_ts=0L;
>         int size = Lists.newArrayList(values).size();
>
>         for (Raw value: values) {
>             if(value.getTs() > end_ts) end_ts = value.getTs();
>             if (value.getTs() < start_ts) start_ts = value.getTs();
>
>             if(last_event_ts == 0L){
>                 last_event_ts = value.getTs();
>             } else {
>                 dwell_time += value.getTs() - last_event_ts;
>                 last_event_ts = value.getTs();
>             }
>         }
>
>         out.collect(new
> Features(tuple.getField(0), tuple.getField(2), tuple.getField(1), start_ts, end_ts, size,
dwell_time, Boolean.FALSE));
>
>
>
> On Tuesday, November 17, 2015 12:59 PM, Stephan Ewen <sewen@apache.org>
> wrote:
>
>
> Hi!
>
> Can you give us a bit more context? For example share the structure of the
> program (what stream get windowed and connected in what way)?
>
> I would guess that the following is the problem:
>
> When you connect one stream to another, then partition n of the first
> stream connects with partition n of the other stream.
> When you do a keyBy().window() then the system reshuffles the data, and
> the records are in different partitions, meaning that they arrive in other
> instances of the CoFlatMapFunction.
>
> You can also call keyBy() before both inputs to make sure that the records
> are properly routed...
>
> Greetings,
> Stephan
>
>
>
> On Tue, Nov 17, 2015 at 12:29 PM, Vladimir Stoyak <vstoyak@yahoo.com>
> wrote:
>
> Got stuck a bit with CoFlatMapFunction. It seems to work fine if I place
> it on the DataStream before window but fails if placed after window's
> “apply” function.
> I was testing two streams, main “Features” on flatMap1 constantly
> ingesting data and control stream “Model” on flatMap2 changing the model on
> request.
> I am able to set and see b0/b1 properly set in flatMap2, but flatMap1
> always see b0 and b1 as was set to 0 at the initialization.
> Am I missing something obvious here?
> Thanks a lot, Vladimir
>
> public static class applyModel implements CoFlatMapFunction<Features, Model, EnrichedFeatures>
{
>     private static final long serialVersionUID = 1L;
>
>     Double b0;
>     Double b1;
>
>     public applyModel(){
>         b0=0.0;
>         b1=0.0;
>     }
>
>     @Override
>     public void flatMap1(Features value, Collector<EnrichedFeatures> out) {
>         System.out.print("Main: " + this + "\n");
>     }
>
>     @Override
>     public void flatMap2(Model value, Collector<EnrichedFeatures> out) {
>         System.out.print("Old Model: " + this + "\n");
>         b0 = value.getB0();
>         b1 = value.getB1();
>         System.out.print("New Model: " + this + "\n");
>     }
>
>     @Override
>     public String toString(){
>         return "CoFlatMapFunction: {b0: " + b0 + ", b1: " + b1 + "}";
>     }}
>
>
>
>
>

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