Randomize the order of block fetches in getMultiple

core/src/main/scala/spark/storage/BlockManager.scala

@@ -316,7 +316,8 @@ class BlockManager(val master: BlockManagerMaster, val serializer: Serializer, m
     // be requested initially and ones that will be added to a queue of blocks to request.
     val initialRequestBlocks = new HashMap[BlockManagerId, ArrayBuffer[BlockMessage]]()
     var initialRequests = 0
-    for ((address, blockIds) <- blocksByAddress) {
+    val blocksToGetLater = new ArrayBuffer[(BlockManagerId, BlockMessage)]
+    for ((address, blockIds) <- Utils.randomize(blocksByAddress)) {
       if (address == blockManagerId) {
         localBlockIds ++= blockIds
       } else {
@@ -328,11 +329,13 @@ class BlockManager(val master: BlockManagerMaster, val serializer: Serializer, m
               .append(blockMessage)
             initialRequests += 1
           } else {
-            blocksToRequest.enqueue((address, blockMessage))
+            blocksToGetLater.append((address, blockMessage))
           }
         }
       }
     }
+    // Add the remaining blocks into a queue to pull later in a random order
+    blocksToRequest ++= Utils.randomize(blocksToGetLater)
 
     // Send out initial request(s) for 'numParallelFetches' blocks.
     for ((bmId, blockMessages) <- initialRequestBlocks) {