Akka-Stream implementation slower than single threaded implementation

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Akka Streams is using asynchronous message passing between Actors to implement stream processing stages. Passing data across an asynchronous boundary has an overhead that you are seeing here: your computation seems to take only about 160ns (derived from the single-threaded measurement) while the streaming solution takes roughly 1µs per element, which is dominated by the message passing.

Another misconception is that saying “stream” implies parallelism: in your code all computation runs sequentially in a single Actor (the map stage), so no benefit can be expected over the primitive single-threaded solution.

In order to benefit from the parallelism afforded by Akka Streams you need to have multiple processing stages that each perform tasks of >1µs per element, see also the docs.

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