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From Gwenhael Pasquiers <gwenhael.pasqui...@ericsson.com>
Subject Making batches of small messages
Date Wed, 11 Jan 2017 16:16:47 GMT

Sorry if this was already asked.

For performances reasons (streaming as well as batch) I'd like to "group" messages (let's
say by batches of 1000) before sending them to my sink (kafka, but mainly ES) so that I have
a smaller overhead.

I've seen the "countWindow" operation but if I'm not wrong the parallelism of such an operation
is 1. Moreover I'd need some "timeout" (send the current batch to next operator after 5s if
it did not reach 1000 messages before that).

I could also create a flatMap "String to List<String>" that cumulates messages until
it reaches 1000 and then sends them to output, however that does not solve the timeout issue
(not sure I could call out.collect() from a Timer thread), and even more importantly I'm afraid
that that would screw up the exactly-once policy (flink could not know that I was stacking
messages, I could very well be filtering them) in case of a crash.

My Sink could also create the chunks, with it's own timer / counter, but I'm also afraid that
it would bread the exactly-once thingie since in case of crash there is no way that flink
would know if the message was really sent or stacked ...

Is there a proper way to do what I want ?

Thanks in advance,


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