title: publishOn vs subscribeOn in Project Reactor 3
body: <p>I am using publishOn vs subscribeOn both on the same flux as follows:</p>
  
  <pre><code>    System.out.println("*********Calling Concurrency************");
      List&lt;Integer&gt; elements = new ArrayList&lt;&gt;();
      Flux.just(1, 2, 3, 4)
        .map(i -&gt; i * 2)
        .log()
        .publishOn(Schedulers.elastic())
        .subscribeOn(Schedulers.parallel())
        .subscribe(elements::add);
      System.out.println("-------------------------------------");
  </code></pre>
  
  <p>Although, when i use both, nothing is printed in logs.
  But when i use only publishOn, i got the following info logs:</p>
  
  <pre><code>*********Calling Concurrency************
  [info] | onSubscribe([Synchronous Fuseable] FluxArray.ArraySubscription)
  [info] | request(256)
  [info] | onNext(1)
  [info] | onNext(2)
  [info] | onNext(3)
  [info] | onNext(4)
  [info] | onComplete()
  -------------------------------------
  </code></pre>
  
  <p>Is that publishOn is more recommended than subscribeOn? Or it has more preference than subscribeOn? What is the difference between the two and when to use which?</p>