[SPARK-6313] Add config option to disable file locks/fetchFile cache to support NFS mounts

Author: nemccarthy

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -403,7 +403,8 @@ private[spark] object Utils extends Logging {
       useCache: Boolean) {
     val fileName = url.split("/").last
     val targetFile = new File(targetDir, fileName)
-    if (useCache) {
+    val fetchCacheEnabled = conf.getBoolean("spark.files.useFetchCache", defaultValue = true)
+    if (useCache && fetchCacheEnabled) {
       val cachedFileName = s"${url.hashCode}${timestamp}_cache"
       val lockFileName = s"${url.hashCode}${timestamp}_lock"
       val localDir = new File(getLocalDir(conf))

docs/configuration.md

@@ -745,6 +745,18 @@ Apart from these, the following properties are also available, and may be useful
     the driver, in seconds.
   </td>
 </tr>
+<tr>
+  <td><code>spark.files.useFetchCache</code></td>
+  <td>true</td>
+  <td>
+    If file fetching should use local caching. The improves performance when running multiple
+    executors on the one host and is enabled by default (see
+    <a href="https://issues.apache.org/jira/browse/SPARK-6313">SPARK-6313</a> for more details).
+    When set to true (default) caching is enabled. When set to false, caching optimizations are
+    switched off and no lock files are created, this allows fetchFiles store to reside on a NFS
+    mount.
+  </td>
+</tr>
 <tr>
   <td><code>spark.files.overwrite</code></td>
   <td>false</td>