Merge pull request #524 from rxin/doc

Added spark.shuffle.file.buffer.kb to configuration doc.

Author: Reynold Xin <rxin@apache.org>

== Merge branch commits ==

commit 0eea1d761ff772ff89be234e1e28035d54e5a7de
Author: Reynold Xin <rxin@apache.org>
Date:   Wed Jan 29 14:40:48 2014 -0800

    Added spark.shuffle.file.buffer.kb to configuration doc.

docs/configuration.md

@@ -398,6 +398,14 @@ Apart from these, the following properties are also available, and may be useful
     If set to "true", consolidates intermediate files created during a shuffle. Creating fewer files can improve filesystem performance for shuffles with large numbers of reduce tasks. It is recommended to set this to "true" when using ext4 or xfs filesystems. On ext3, this option might degrade performance on machines with many (>8) cores due to filesystem limitations.
   </td>
 </tr>
+<tr>
+  <td>spark.shuffle.file.buffer.kb</td>
+  <td>100</td>
+  <td>
+    Size of the in-memory buffer for each shuffle file output stream, in kilobytes. These buffers
+    reduce the number of disk seeks and system calls made in creating intermediate shuffle files.
+  </td>
+</tr>
 <tr>
   <td>spark.shuffle.spill</td>
   <td>true</td>