title: Back pressure in RxJava2
body: <p>Supposed that I have 1 million lines of records in a database. Then I use Flowable (instead Observable) to read the records then write them into a file with slow encryption writing (writing is much slower than reading). </p>
  
  <p>If I don't use <a href="https://github.com/ReactiveX/RxJava/wiki/Backpressure" rel="nofollow noreferrer">"reactive pull"</a> during the writing, is it possible that my memory is populated with those 1 million records while the writing process is still half-way? In other words, is it possible to have out of memory exception?</p>
  
  <p>If yes, is using "reactive pull" is the only way to prevent that exception, if I also don't want to use operators like throttling, etc.</p>