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From "bupt_ljy"<bupt_...@163.com>
Subject Re: Finite source without blocking save-points
Date Mon, 04 Nov 2019 14:59:02 GMT
Hi Gael,
I had a similar situation before. Actually you don’t need to accomplish this in such a complicated
way. I guess you’ve already had a rules source and you can send rules in #open function
for a startup if your rules source inherit from #RichParallelSourceFunction.


Best,
Jiayi Liao


 Original Message 
Sender: Gaël Renoux<gael.renoux@datadome.co>
Recipient: user<user@flink.apache.org>
Date: Monday, Nov 4, 2019 22:50
Subject: Finite source without blocking save-points


Hello everyone,


I have a job which runs continuously, but it also needs to send a single specific Kafka message
on startup. I tried the obvious approach to use StreamExecutionEnvironment.fromElements and
add a Kafka sink, however that's not possible: the source being finished, it becomes impossible
to stop the job with a save-point later.



The best solution I found is creating a basic Kafka producer to send the message, and running
that producer inside the job's startup script (before calling StreamExecutionEnvironment.execute()).
However, there's a race condition, where the message could be sent and trigger stuff before
the job is ready to receive messages. In addition, it forces me to have a separate Kafka producer,
while Flink already comes with Kafka sinks. And finally, it's pretty specific to my use case
(sending a Kafka message), and it looks like there should be a generic solution here.



Do you guys know of any better way to do this? Is there any way to set up a finite source
that will not block save-points?



Just in case, the global use case is nothing special: my job maintains a set of rules as broadcast
state in operators and handle input according to those rules. On startup, I need to request
all rules to be sent at once (the emitter normally sends updated rules only), in case the
rule state has been lost (happens when we evolve the rule model, for instance), and this is
done through a Kafka message.


Thanks in advance!



Gaël Renoux
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