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From Ivan Wang <ivan.w...@augmentum.com>
Subject Re: Is Flink able to do real time stock market analysis?
Date Thu, 12 Apr 2018 13:52:52 GMT
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 <mlatta@technomage.com>
Date: Thursday, 12 April 2018 at 3:21 AM
To: Ivan Wang <ivan.wang2010@gmail.com>
Cc: "user@flink.apache.org" <user@flink.apache.org>
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 <ivan.wang2010@gmail.com<mailto:ivan.wang2010@gmail.com>>
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 window.group(). 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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