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From Radu Tudoran <radu.tudo...@huawei.com>
Subject RE: Question about the process order in stream aggregate
Date Tue, 11 Apr 2017 12:40:15 GMT
Hi Xingcan,

If you need to guarantee the order also in the case of procTime a trick that you can do is
to set the working time of the env to processing time and to assign the proctime to the incoming
stream. You can do this via .assignTimestampsAndWatermarks(new ...)
And override 
override def extractTimestamp(
      element: type...,
      previousElementTimestamp: Long): Long = {
      System.currentTimeMillis()
    }

Alternatively you can play around with the stream source and control the time when the events
come

Dr. Radu Tudoran
Senior Research Engineer - Big Data Expert
IT R&D Division


HUAWEI TECHNOLOGIES Duesseldorf GmbH
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-----Original Message-----
From: fhueske@gmail.com [mailto:fhueske@gmail.com] 
Sent: Tuesday, April 11, 2017 2:24 PM
To: Stefano Bortoli; dev@flink.apache.org
Subject: AW: Question about the process order in stream aggregate

Resending to dev@f.a.o

Hi Xingcan,

This is expected behavior. In general, is not possible to guarantee results for processing
time.

Your query is translated as follows:

CollectionSrc(1) -round-robin-> MapFunc(n) -hash-part-> ProcessFunc(n) -fwd-> MapFunc(n)
-fwd-> Sink(n)

The order of records is changed because of the connection between source and first map function.
Here, records are distributed round robin to increase the parallelism from 1 to n. The parallel
instances of map might forward the records in different order to the ProcessFunction that
computes the aggregation. 

Hope this helps,
Fabian


Von: Stefano Bortoli
Gesendet: Dienstag, 11. April 2017 14:10
An: dev@flink.apache.org
Betreff: RE: Question about the process order in stream aggregate

Hi Xingcan,

Are you using parallelism 1 for the test?  procTime semantics deals with the objects as they
loaded in the operators. It could be the co-occuring partitioned events (in the same MS time
frame) are processed in parallel and then the output is produced in different order.

I suggest you to have a look at the integration test to verify that the configuration of your
experiment is correct.

Best,
Stefano

-----Original Message-----
From: Xingcan Cui [mailto:xingcanc@gmail.com] 
Sent: Tuesday, April 11, 2017 5:31 AM
To: dev@flink.apache.org
Subject: Question about the process order in stream aggregate

Hi all,

I run some tests for stream aggregation on rows. The data stream is simply registered as

val orderA: DataStream[Order] = env.fromCollection(Seq(
      Order(1L, "beer", 1),
      Order(2L, "diaper", 2),
      Order(3L, "diaper", 3),
      Order(4L, "rubber", 4)))
tEnv.registerDataStream("OrderA", orderA, 'user, 'product, 'amount),

and the SQL is defined as

select product, sum(amount) over (partition by product order by procTime() rows between unbounded
preceding and current row from orderA).

My expected output should be

2> Result(beer,1)
2> Result(diaper,2)
1> Result(rubber,4)
2> Result(diaper,5).

However, sometimes I get the following output

2> Result(beer,1)
2> Result(diaper,3)
1> Result(rubber,4)
2> Result(diaper,5).

It seems that the row "Order(2L, "diaper", 2)" and "Order(3L, "diaper", 3)"
are out of order. Is that normal?

BTW, when I run `orderA.keyBy(2).map{x => x.amount + 1}.print()`, the order for them can
always be preserved.

Thanks,
Xingcan

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