title: Spark Streaming: Persist not working
body: <p>I have 2 streams. Stream1 receives data occasonally, usually only in first batch. Stream2 constantly receives data. I want to left outer join Stream2 to all the data Stream1 has received. I tried the following, but it's failing to account previous batches received in Stream1.</p>
  
  <pre><code>val s1 = ssc.receiverStream(new CustomReceiver(1005))
  val s1p = s1.map...
  val s2 = ssc.receiverStream(new CustomReceiver(1006)).persist()
  val s2p = s2.map....persist()
  val joined = s2p.leftOuterJoin(s1p)
  </code></pre>
  
  <p>In the logs, I see messages about removing Stream2's RDDs from persistence list.</p>