Hi Min,
Please feel welcomed in the Flink community. One small remark, dev mailing list
is for developers of Flink and all of the issues/discussions that arise in the
process (discussing how to implement new feature etc), so user mailing list is
the right one to ask questions about using Flink :)
Asking your question, Flink doesn’t guarantee order of the elements and
especially not when it involves multiple parallel operators. The order can
brake whenever there is some network exchange/transfer between operators/tasks,
for example after using `keyBy`, `rebalance` or on the border of changing
parallelism. Locally, within one instance of your Fold function, order is
preserved. In other words, if you need some elements order to process records,
you have to make sure that it’s there, for example:
env.addSrouce(….)
.keyBy(….)
.process(new MyElementsSorter())
.fold(…)
However keep in mind that sorting records in an infinite data stream is a quite
tricky concept unless it’s only a “best effort". Usually you would probably
like to group records into a window and process those windows.
Piotrek
> On 7 Dec 2018, at 09:12, min....@ubs.com wrote:
>
> Hi,
>
> 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.
>
> Regards,
>
> Min
>
> -------------------------------------------------------------------
> 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>() {
> @Override
> public String fold(String current, Integer value) {
> return current + "-" + value;
> }
> });
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> From: jincheng sun [mailto:sunjincheng...@gmail.com
> <mailto:sunjincheng...@gmail.com>]
> Sent: Freitag, 7. Dezember 2018 02:24
> To: rakkukumar2...@gmail.com <mailto:rakkukumar2...@gmail.com>
> Cc: user@flink.apache.org <mailto:user@flink.apache.org>;
> d...@flink.apache.org <mailto:d...@flink.apache.org>
> 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.:
> orderStream
> .keyBy(<KeySelector>)
> .intervalJoin(invoiceStream.keyBy(<KeySelector>))
> .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
>
> <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!
>
> Bests,
> Jincheng
>
>
> Rakesh Kumar <rakkukumar2...@gmail.com <mailto:rakkukumar2...@gmail.com>>
> 于2018年12月6日周四 下午7:10写道：
> Hi,
> 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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