[GitHub] kl0u commented on issue #6687: [FLINK-10327][streaming] Expose processWatermarks notifications to (Co)ProcessFunction

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kl0u commented on issue #6687: [FLINK-10327][streaming] Expose processWatermarks notifications to (Co)ProcessFunction
URL: https://github.com/apache/flink/pull/6687#issuecomment-421017411
 
 
   Hi @pnowojski ! 
   
   I can understand that this can be an interesting addition for some usecases, but it is a big one, and it should be discussed more thoroughly and, most importantly, more publicly. I would be against merging it as just a sub-commit of another feature.
   
   The reason is that this allows users to "play" with watermarks from the level of a `Function` and not `Operator`, which was, intentionally, the case so far.
   
   If you want to "hold back" the watermark, the this should be done by a watermark assigner.
   
   If you want to run a "callback" upon watermark, then so far the trick is to register a timer for `watermark + 1`. 
   
   I can find usecases which do not fall into any of the above, but for those so far we implement custom operators. 

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