Given the data from a window can not arrive before any of the data in that 
window, it will always arrive after the raw data for the same period, and may 
have some latency relative to the raw data.  If your RichFlatMapFunction uses a 
ListState to hold more than one window worth of raw and smoothed data, you 
should be able to get what you want.  Given distributed systems and relative 
time I am not sure you will get simpler than that.


> On Apr 12, 2018, at 7:52 AM, Ivan Wang <> wrote:
> Thanks Michael very much, it helps a lot! 
> I tried what you suggest and now I can compare smoothed data with raw date in 
> coFlat method.
> However, it cannot ensure that the smoothed data is coming in the expected 
> way.  Basically for every raw event, I’d like to refer to the early but 
> closest event in smoothed data. However, it cannot be guaranteed by default. 
> For example, we raw event comes with event time 13:01:39, I’d like to refer 
> to smoothed event with event time 13:01:30 due to 15 seconds interval. But 
> the latter only arrives after raw event 13:01:58, this happens at least in 
> batch processing when I did historical analysis.  
> I corrected the order by using key state in coFlatMap method. I stored the 
> latest smoothed event and queued raw event if they arrive too early.
> My question is that is there any better and straightforward way to correct 
> the order? Because it makes the code hard to read. I’m thinking about 
> watermark, but not sure how to do this.
> -- 
> Thanks
> Ivan
> From: TechnoMage <>
> Date: Thursday, 12 April 2018 at 3:21 AM
> To: Ivan Wang <>
> Cc: "" <>
> Subject: Re: Is Flink able to do real time stock market analysis?
> I am new to Flink so others may have more complete answer or correct me. <>
> If you are counting the events in a tumbling window you will get output at 
> the end of each tumbling window, so a running count of events/window.  It 
> sounds like you want to compare the raw data to the smoothed data?  You can 
> use a CoFlatMap to receive both streams and output any records you like, say 
> a Tuple with the raw and smoothed value.  If you use a RichCoFlatMap you can 
> track state, so you could keep a list of the last 20 or so raw and smoothed 
> values so you can align them.
> Michael
> On Apr 10, 2018, at 6:40 PM, Ivan Wang < 
> <>> wrote:
> Hi all, 
> I've spent nearly 2 weeks trying to figure a solution to my requirement as 
> below. If anyone can advise, that would be great.
> 1. There're going to be 2000 transactions per second as StreamRaw, I'm going 
> to tumbleWindow them as StreamA, let's say every 15 seconds. Then I'm going 
> to countWindow StreamA as StreamB, let's say every 20 events.
> 2. For every event in  StreamRaw as E, I need to find exact one event in 
> StreamB which is earlier than E and closest to E. Then some comparison will 
> be proceeded. For example, if timestamp in E is 9:46:38, there should be an 
> event in StreamB with timestamp 9:46:30 because I use 15 seconds interval. 
> I tried CEP using StreamRaw, however, I didn't figure out how to involve 
> StreamB and get the exact one event in condition method.
> I tried tableAPI and SQL, it throws time attribute error during the second 
> window method. 
> window(Tumble).group().select().window(Slide).group().select()
> Seems there's no way to tell Flink the time attribute after the first 
> I then tried to convert it into table first then leftoutJoin 
> them. But Flink tells me it's not supported.
> Is Flink able to do this? If not, I'll go for other alternatives. Thanks 
> again if someone can help.

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