From cd35b692de88e3afe7f41405da635c3fbd9b4650 Mon Sep 17 00:00:00 2001
From: Eric Payne <epayne@apache.org>
Date: Tue, 10 May 2016 15:45:01 +0000
Subject: [PATCH] MAPREDUCE-6678. Allow ShuffleHandler readahead without
 drop-behind. Contributed by Nathan Roberts.

---
 .../main/java/org/apache/hadoop/mapred/FadvisedFileRegion.java  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-shuffle/src/main/java/org/apache/hadoop/mapred/FadvisedFileRegion.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-shuffle/src/main/java/org/apache/hadoop/mapred/FadvisedFileRegion.java
index 6fd46a5310..cb9b5e088e 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-shuffle/src/main/java/org/apache/hadoop/mapred/FadvisedFileRegion.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-shuffle/src/main/java/org/apache/hadoop/mapred/FadvisedFileRegion.java
@@ -74,7 +74,7 @@ public FadvisedFileRegion(RandomAccessFile file, long position, long count,
   @Override
   public long transferTo(WritableByteChannel target, long position)
       throws IOException {
-    if (manageOsCache && readaheadPool != null) {
+    if (readaheadPool != null && readaheadLength > 0) {
       readaheadRequest = readaheadPool.readaheadStream(identifier, fd,
           getPosition() + position, readaheadLength,
           getPosition() + getCount(), readaheadRequest);