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From Xingcan Cui <xingc...@gmail.com>
Subject Re: Slow watermark advances
Date Fri, 13 Apr 2018 16:49:41 GMT
Hi Chengzhi,

currently, the watermarks of the two streams of a connected stream are forcibly synchronized,
i.e., the watermark is decided by the stream with a larger delay. Thus the window trigger
is also affected by this mechanism. 

As a workaround, you could try to add (or subtract) a static time offset to one of your streams,
which can make them more “close” to each other.


> On 13 Apr 2018, at 11:48 PM, Chengzhi Zhao <w.zhaochengzhi@gmail.com> wrote:
> Hi, flink community,
> I had an issue with slow watermark advances and needs some help here. So here is what
happened: I have two streams -- A and B, and they perform co-process to join together and
A has another steam as output. 
> A --> Output
> B --> (Connect A) --> Output
> I used BoundedOutOfOrdernessGenerator [1] with both A and B stream with 2 hours delay.
The low watermark of A and output sink is within 2 hours window, however, the co-process end
up with 10 hours low watermark late.
> My setup is I am using file system as source, so every 15 mins there will be files been
drop to a directory and flink pick them up from there. 
> Please advise and appreciate it in advance!
> [1] https://ci.apache.org/projects/flink/flink-docs-release-1.4/dev/event_timestamps_watermarks.html#with-periodic-watermarks
> Best,
> Chengzhi

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