Re: Publishing Sink Task watermarks outside flink

Posted by Shubham Kumar on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/Publishing-Sink-Task-watermarks-outside-flink-tp34765p34783.html

Hi Timo,

Yeah, I got the idea of getting access to timers through process function and had the same result which you explained 

that is a side output doesn't guarantee that the data is written out to sink. (so maybe Fabian in that post pointed out something

else which I am missing). If I am correct then, data is written to side output as soon as it is processed in the Process function (maybe in 

process function itself on Ontimer call if a timer has been set, right?

I am doing all computation in Datastream<Object> and then adding a mapper to convert to DataStream<Row> to sink through JdbcAppendTableSink

which is part of Table API I think. I will definitely try exploring the Jdbc Sink function and context to get the watermark.

Thinking out of the box, is it possible to add some extra operator after sink which will always have watermark which is greater than sink function watermarks,

as its a downstream operator.

Also, does the problem simplify if we have Kafka sink?

On Tue, Apr 28, 2020 at 10:35 PM Timo Walther <[hidden email]> wrote:

Hi Shubham,

you can call stream.process(...). The context of ProcessFunction gives
you access to TimerService which let's you access the current watermark.

I'm assuming your are using the Table API? As far as I remember,
watermark are travelling through the stream even if there is no
time-based operation happening. But you should double check that.

However, a side output does not guarantee that the data has already been
written out to the sink. So I would recommend to customize the JDBC sink
instead and look into the row column for getting the current timestamp.

Or even better, there should also be
org.apache.flink.streaming.api.functions.sink.SinkFunction.Context with
access to watermark.

I hope this helps.

Regards,
Timo

On 28.04.20 13:07, Shubham Kumar wrote:
> Hi everyone,
>
> I have a flink application having kafka sources which calculates some
> stats based on it and pushes it to JDBC. Now, I want to know till what
> timestamp is the data completely pushed in JDBC (i.e. no more data will
> be pushed to timestamp smaller or equal than this). There doesn't seem
> to be any direct programmatic way to do so.
>
> I came across the following thread which seemed most relevant to my
> problem:
> http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/End-of-Window-Marker-td29345.html#a29461
>
> However, I can't seem to understand how to chain a process function
> before the sink task so as to put watermarks to a side output. (I
> suspect it might have something to do with datastream.addSink in regular
> datastream sinks vs sink.consumeDataStream(stream) in JDBCAppendTableSink).
>
> Further what happens if there are no windows, how to approach the
> problem then?
>
> Please share any pointers or relevant solution to tackle this.
>
> --
> Thanks & Regards
>
> Shubham Kumar
>

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