svn merge -c 1532915 Merging from trunk to branch-2 to fix HDFS-5346.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1532916 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -3489,6 +3489,9 @@ Release 0.23.10 - UNRELEASED
     HDFS-5010. Reduce the frequency of getCurrentUser() calls from namenode
     (kihwal)
 
+    HDFS-5346. Avoid unnecessary call to getNumLiveDataNodes() for each block 
+    during IBR processing (Ravi Prakash via kihwal)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -4601,7 +4601,7 @@ private synchronized boolean canLeave() {
      */
     private boolean needEnter() {
       return (threshold != 0 && blockSafe < blockThreshold) ||
-        (getNumLiveDataNodes() < datanodeThreshold) ||
+        (datanodeThreshold != 0 && getNumLiveDataNodes() < datanodeThreshold) ||
         (!nameNodeHasResourcesAvailable());
     }