Is it necessary to use windows in Flink?

Question

I'm attempting to transform a stream of data, without using any window provided by Flink. My code looks something like this :

val stream1 = executionEnvironment.getStream
val stream2 = stream1.flatMap(someFunction)

stream2.addSink(s3_Sink)
executionEnvironment.execute()

However, upon submitting and running my job, I'm not getting any output on S3. The web UI shows 0 bytes received, 0 records received, 0 bytes sent, 0 records sent.

Another running Flink job is already using the same data source, so the data source is fine. There are no errors anywhere but still no output. Could this issue be, because I'm not using any window or key operation? I attempted to get the output after assigning ascending timestamps but didn't get any output. Any idea of what could not be working?

Answer 1

I guess that has nothing to do with a missing window. Rule of thumb: Use windows when you want any kind of aggregation (folds, reduces, etc.).

Regarding you initial problem: From what you have shown so far I can only imagine that the flatMap operator doesn't produces any output (in contrast to a map which always have to emit a value flatMap might filter out everything). Maybe you can add more code so that we can have a closer look.