reactor-core/src/main/java/reactor/core/publisher/ParallelFlux.java
public final Flux<T> sequential(int prefetch) {
		return Flux.onAssembly(new ParallelMergeSequential<>(this,
				prefetch,
				Queues.get(prefetch)));
	}
public final Flux<T> sequential(int prefetch) {
		return Flux.onAssembly(new ParallelMergeSequential<>(this,
				prefetch,
				Queues.get(prefetch)));
	}
Merges the values from each 'rail' in a round-robin or same-order fashion and
exposes it as a regular Publisher sequence, running with a give prefetch value for
the rails.

@param prefetch the prefetch amount to use for each rail

@return the new Flux instance