HDFS-2751. Datanode may incorrectly drop OS cache behind reads even for short reads. Contributed by Todd Lipcon.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1233796 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -340,6 +340,9 @@ Release 0.23.1 - UNRELEASED
 
     HDFS-2810. Leases not getting renewed properly by clients (todd)
 
+    HDFS-2751. Datanode may incorrectly drop OS cache behind reads
+    even for short reads. (todd)
+
 Release 0.23.0 - 2011-11-01 
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockSender.java

@@ -315,7 +315,7 @@ class BlockSender implements java.io.Closeable {
    * close opened files.
    */
   public void close() throws IOException {
-    if (blockInFd != null && shouldDropCacheBehindRead) {
+    if (blockInFd != null && shouldDropCacheBehindRead && isLongRead()) {
       // drop the last few MB of the file from cache
       try {
         NativeIO.posixFadviseIfPossible(