HDFS-5197. Document dfs.cachereport.intervalMsec in hdfs-default.xml. Contributed by Chris Nauroth.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4949@1523543 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-4949.txt

@@ -36,6 +36,9 @@ HDFS-4949 (Unreleased)
     HDFS-5053. NameNode should invoke DataNode APIs to coordinate caching.
     (Andrew Wang)
 
+    HDFS-5197. Document dfs.cachereport.intervalMsec in hdfs-default.xml.
+    (cnauroth)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -1419,6 +1419,17 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.namenode.caching.enabled</name>
+  <value>false</value>
+  <description>
+    Set to true to enable block caching.  This flag enables the NameNode to
+    maintain a mapping of cached blocks to DataNodes via processing DataNode
+    cache reports.  Based on these reports and addition and removal of caching
+    directives, the NameNode will schedule caching and uncaching work.
+  </description>
+</property>
+
 <property>
   <name>dfs.datanode.max.locked.memory</name>
   <value>0</value>
@@ -1428,7 +1439,10 @@
     (RLIMIT_MEMLOCK) must be set to at least this value, else the datanode
     will abort on startup.
 
-    By default, this parameter set to 0, which disables in-memory caching.
+    By default, this parameter is set to 0, which disables in-memory caching.
+
+    If the native libraries are not available to the DataNode, this
+    configuration has no effect.
   </description>
 </property>
 
@@ -1442,4 +1456,21 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.cachereport.intervalMsec</name>
+  <value>10000</value>
+  <description>
+    Determines cache reporting interval in milliseconds.  After this amount of
+    time, the DataNode sends a full report of its cache state to the NameNode.
+    The NameNode uses the cache report to update its map of cached blocks to
+    DataNode locations.
+
+    This configuration has no effect if in-memory caching has been disabled by
+    setting dfs.datanode.max.locked.memory to 0 (which is the default).
+
+    If the native libraries are not available to the DataNode, this
+    configuration has no effect.
+  </description>
+</property>
+
 </configuration>