Exactly the same as merge.
Prefer to flatMap for transforming a subset of items like optionMap but convenient with case syntax in scala prod.
Merge a different type of Producer into a single stream
Keep only the items that satisfy the fn
Only use this function if you may return more than 1 item sometimes.
This is identical to a certain leftJoin: map((_, ())).
Map each item to a new value
Combine the output into one Producer
Naming a node is so that you may give Options for that node that may change the run-time performance of the job (parameter tuning, etc.
Prefer this or collect to flatMap if you are always emitting 0 or 1 items
Cause some side effect on the sink, but pass through the values so they can be consumed downstream