HDFS-7685. Document dfs.namenode.heartbeat.recheck-interval in hdfs-default.xml. Contributed by Kai Sasaki.

(cherry picked from commit 8719cdd4f68abb91bf9459bca2a5467dafb6b5ae)

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

@@ -387,6 +387,9 @@ Release 2.7.0 - UNRELEASED
     HDFS-7308. Change the packet chunk size computation in DFSOutputStream in
     order to enforce packet size <= 64kB.  (Takuya Fukudome via szetszwo)
 
+    HDFS-7685. Document dfs.namenode.heartbeat.recheck-interval in
+    hdfs-default.xml. (Kai Sasaki via aajisaka)
+
   OPTIMIZATIONS
 
     HDFS-7454. Reduce memory footprint for AclEntries in NameNode.

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

@@ -144,6 +144,17 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.namenode.heartbeat.recheck-interval</name>
+  <value>300000</value>
+  <description>
+    This time decides the interval to check for expired datanodes.
+    With this value and dfs.heartbeat.interval, the interval of
+    deciding the datanode is stale or not is also calculated.
+    The unit of this configuration is millisecond.
+  </description>
+</property>
+
 <property>
   <name>dfs.http.policy</name>
   <value>HTTP_ONLY</value>