merge MAPREDUCE-3718 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1236360 13f79535-47bb-0310-9956-ffa450edef68

hadoop-mapreduce-project/CHANGES.txt

@@ -155,6 +155,9 @@ Release 0.23.1 - Unreleased
     MAPREDUCE-3512. Batching JobHistory flushing to DFS so that we don't flush
     for every event slowing down AM. (Siddarth Seth via vinodkv)
 
+    MAPREDUCE-3718. Change default AM heartbeat interval to 1 second. (Hitesh
+    Shah via sseth)
+
   BUG FIXES
     MAPREDUCE-3194. "mapred mradmin" command is broken in mrv2
                      (Jason Lowe via bobby)

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/MRJobConfig.java

@@ -417,7 +417,7 @@ public interface MRJobConfig {
   /** How often the AM should send heartbeats to the RM.*/
   public static final String MR_AM_TO_RM_HEARTBEAT_INTERVAL_MS =
     MR_AM_PREFIX + "scheduler.heartbeat.interval-ms";
-  public static final int DEFAULT_MR_AM_TO_RM_HEARTBEAT_INTERVAL_MS = 2000;
+  public static final int DEFAULT_MR_AM_TO_RM_HEARTBEAT_INTERVAL_MS = 1000;
 
   /**
    * If contact with RM is lost, the AM will wait MR_AM_TO_RM_WAIT_INTERVAL_MS