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A question on the Flink "rolling" FoldFunction



I am new to Flink. I have a question on this "rolling" fold function.


If its parallelism is large than one, does the "rolling" order remains the same? i.e. it is always keep the "1-2-3-4-5" on an increasing sequence.






------------------------------------------------------------------- FoldFunction ---------------------------------------------------------------------------------------------------------------

A "rolling" fold on a keyed data stream with an initial value. Combines the current element with the last folded value and emits the new value. 

A fold function that, when applied on the sequence (1,2,3,4,5), emits the sequence "start-1", "start-1-2", "start-1-2-3", ...

DataStream<String> result =
  keyedStream.fold("start", new FoldFunction<Integer, String>() {
    public String fold(String current, Integer value) {
        return current + "-" + value;



From: jincheng sun [mailto:sunjincheng121@xxxxxxxxx]
Sent: Freitag, 7. Dezember 2018 02:24
To: rakkukumar2707@xxxxxxxxx
Cc: user@xxxxxxxxxxxxxxxx; dev@xxxxxxxxxxxxxxxx
Subject: [External] Re: delay one of the datastream when performing join operation on event-time and watermark


Hi Pakesh Kuma,

I think you can using the interval-join, e.g.:

    .between(Time.minutes(-5), Time.minutes(5))

The semantics of interval-join and detailed usage description can refer to https://ci.apache.org/projects/flink/flink-docs-release-1.7/dev/stream/operators/joining.html#interval-join


Hope to help you, and any feedback is welcome!






Rakesh Kumar <rakkukumar2707@xxxxxxxxx> 2018126日周四 下午7:10写道:


I have two data sources one is  for order data and another one is for invoice data, these two data i am pushing into kafka topic in json form. I wanted to delay order data for 5 mins because invoice data comes only after order data is generated. So, for that i have written a flink program which will take these two data from kafka and apply watermarks and delay order data for 5 mins. After applying watermarks on these data, i wanted to join these data based on order_id which is present in both order and invoice data. After Joining i wanted to push it to kafka in different topic.


But, i am not able to join these data streams with 5 min delay and i am not able to figure it out.


I am attaching my flink program below and it's dependency.

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