The reason why you are struggling to find a solution is that your challenge is not something we would call a merge. To do this properly we would need a 'join'.
As mentioned, this is not a typical thing that you want to do with Nifi. Maybe you can find a workaround by using merge creativity, but the real solution is to use a streaming engine that is capable of streaming joins, like Spark.
- Dennis Jaheruddin
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