vanzin commented on a change in pull request #25299: [SPARK-27651][Core] Avoid 
the network when shuffle blocks are fetched from the same host
URL: https://github.com/apache/spark/pull/25299#discussion_r315841144
 
 

 ##########
 File path: 
core/src/main/scala/org/apache/spark/storage/ShuffleBlockFetcherIterator.scala
 ##########
 @@ -74,16 +76,22 @@ final class ShuffleBlockFetcherIterator(
     maxReqSizeShuffleToMem: Long,
     detectCorrupt: Boolean,
     detectCorruptUseExtraMemory: Boolean,
-    shuffleMetrics: ShuffleReadMetricsReporter)
+    shuffleMetrics: ShuffleReadMetricsReporter,
+    enableHostLocalDiskReading: Boolean = true)
   extends Iterator[(BlockId, InputStream)] with DownloadFileManager with 
Logging {
 
   import ShuffleBlockFetcherIterator._
 
+  // Make remote requests at most maxBytesInFlight / 5 in length; the reason 
to keep them
+  // smaller than maxBytesInFlight is to allow multiple, parallel fetches from 
up to 5
+  // nodes, rather than blocking on reading output from one node.
+  val targetRemoteRequestSize = math.max(maxBytesInFlight / 5, 1L)
+
   /**
    * Total number of blocks to fetch. This should be equal to the total number 
of blocks
    * in [[blocksByAddress]] because we already filter out zero-sized blocks in 
[[blocksByAddress]].
    *
-   * This should equal localBlocks.size + remoteBlocks.size.
+   * This should equal localBlocks.size + remoteBlocks.size + 
hostLocalBlocks.size
 
 Review comment:
   Since you're updating this, you're removing `remoteBlocks`, so...

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