[SPARK-4671][Streaming]Do not replicate streaming block when WAL is enabled

Currently streaming block will be replicated when specific storage level is set, since WAL is already fault tolerant, so replication is needless and will hurt the throughput of streaming application.

Hi tdas , as per discussed about this issue, I fixed with this implementation, I'm not is this the way you want, would you mind taking a look at it? Thanks a lot.

Author: jerryshao <saisai.shao@intel.com>

Closes #3534 from jerryshao/SPARK-4671 and squashes the following commits:

500b456 [jerryshao] Do not replicate streaming block when WAL is enabled

streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceivedBlockHandler.scala

@@ -121,6 +121,24 @@ private[streaming] class WriteAheadLogBasedBlockHandler(
   private val maxFailures = conf.getInt(
     "spark.streaming.receiver.writeAheadLog.maxFailures", 3)
 
+  private val effectiveStorageLevel = {
+    if (storageLevel.deserialized) {
+      logWarning(s"Storage level serialization ${storageLevel.deserialized} is not supported when" +
+        s" write ahead log is enabled, change to serialization false")
+    }
+    if (storageLevel.replication > 1) {
+      logWarning(s"Storage level replication ${storageLevel.replication} is unnecessary when " +
+        s"write ahead log is enabled, change to replication 1")
+    }
+
+    StorageLevel(storageLevel.useDisk, storageLevel.useMemory, storageLevel.useOffHeap, false, 1)
+  }
+
+  if (storageLevel != effectiveStorageLevel) {
+    logWarning(s"User defined storage level $storageLevel is changed to effective storage level " +
+      s"$effectiveStorageLevel when write ahead log is enabled")
+  }
+
   // Manages rolling log files
   private val logManager = new WriteAheadLogManager(
     checkpointDirToLogDir(checkpointDir, streamId),
@@ -156,7 +174,7 @@ private[streaming] class WriteAheadLogBasedBlockHandler(
     // Store the block in block manager
     val storeInBlockManagerFuture = Future {
       val putResult =
-        blockManager.putBytes(blockId, serializedBlock, storageLevel, tellMaster = true)
+        blockManager.putBytes(blockId, serializedBlock, effectiveStorageLevel, tellMaster = true)
       if (!putResult.map { _._1 }.contains(blockId)) {
         throw new SparkException(
           s"Could not store $blockId to block manager with storage level $storageLevel")