HDFS-14632. Reduce useless #getNumLiveDataNodes call in SafeModeMonitor. Contributed by He Xiaoqiao.

(cherry picked from commit 993dc8726b)
(cherry picked from commit 69f1c8d77b)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManagerSafeMode.java

@@ -309,6 +309,7 @@ class BlockManagerSafeMode {
       }
     }
 
+    if (datanodeThreshold > 0) {
       int numLive = blockManager.getDatanodeManager().getNumLiveDataNodes();
       if (numLive < datanodeThreshold) {
         msg += String.format(
@@ -320,6 +321,9 @@ class BlockManagerSafeMode {
                 + "the minimum number %d. ",
             numLive, datanodeThreshold);
       }
+    } else {
+      msg += "The minimum number of live datanodes is not required. ";
+    }
 
     if (getBytesInFuture() > 0) {
       msg += "Name node detected blocks with generation stamps " +

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestSafeMode.java

@@ -201,11 +201,11 @@ public class TestSafeMode {
     final NameNode nn = cluster.getNameNode();
     
     String status = nn.getNamesystem().getSafemode();
-    assertEquals("Safe mode is ON. The reported blocks 0 needs additional " +
-        "14 blocks to reach the threshold 0.9990 of total blocks 15." + NEWLINE +
-        "The number of live datanodes 0 has reached the minimum number 0. " +
-        "Safe mode will be turned off automatically once the thresholds " +
-        "have been reached.", status);
+    assertEquals("Safe mode is ON. The reported blocks 0 needs additional "
+        + "14 blocks to reach the threshold 0.9990 of total blocks 15."
+        + NEWLINE + "The minimum number of live datanodes is not required. "
+        + "Safe mode will be turned off automatically once the thresholds have "
+        + "been reached.", status);
     assertFalse("Mis-replicated block queues should not be initialized " +
         "until threshold is crossed",
         NameNodeAdapter.safeModeInitializedReplQueues(nn));

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestBlockManagerSafeMode.java

@@ -456,6 +456,31 @@ public class TestBlockManagerSafeMode {
     assertTrue(tip.contains("Safe mode will be turned off automatically soon"));
   }
 
+  /**
+   * Test get safe mode tip without minimum number of live datanodes required.
+   */
+  @Test
+  public void testGetSafeModeTipsWithoutNumLiveDatanode() throws IOException {
+    Configuration conf = new HdfsConfiguration();
+    conf.setDouble(DFSConfigKeys.DFS_NAMENODE_SAFEMODE_THRESHOLD_PCT_KEY,
+        THRESHOLD);
+    conf.setInt(DFSConfigKeys.DFS_NAMENODE_SAFEMODE_EXTENSION_KEY,
+        EXTENSION);
+    conf.setInt(DFSConfigKeys.DFS_NAMENODE_SAFEMODE_MIN_DATANODES_KEY, 0);
+
+    NameNode.initMetrics(conf, NamenodeRole.NAMENODE);
+
+    BlockManager blockManager = spy(new BlockManager(fsn, false, conf));
+
+    BlockManagerSafeMode safeMode = new BlockManagerSafeMode(blockManager,
+        fsn, false, conf);
+    safeMode.activate(BLOCK_TOTAL);
+    String tip = safeMode.getSafeModeTip();
+
+    assertTrue(tip.contains("The minimum number of live datanodes is not "
+        + "required."));
+  }
+
   /**
    * Test get safe mode tip in case of blocks with future GS.
    */

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestHASafeMode.java

@@ -493,13 +493,22 @@ public class TestHASafeMode {
     int numNodes, int nodeThresh) {
     String status = nn.getNamesystem().getSafemode();
     if (safe == total) {
+      if (nodeThresh == 0) {
+        assertTrue("Bad safemode status: '" + status + "'",
+            status.startsWith("Safe mode is ON. The reported blocks " + safe
+                + " has reached the " + "threshold 0.9990 of total blocks "
+                + total + ". The minimum number of live datanodes is not "
+                + "required. In safe mode extension. Safe mode will be turned "
+                + "off automatically"));
+      } else {
         assertTrue("Bad safemode status: '" + status + "'",
             status.startsWith(
-            "Safe mode is ON. The reported blocks " + safe + " has reached the "
-            + "threshold 0.9990 of total blocks " + total + ". The number of "
-            + "live datanodes " + numNodes + " has reached the minimum number "
-            + nodeThresh + ". In safe mode extension. "
-            + "Safe mode will be turned off automatically"));
+                "Safe mode is ON. The reported blocks " + safe + " has reached "
+                    + "the threshold 0.9990 of total blocks " + total + ". The "
+                    + "number of live datanodes " + numNodes + " has reached "
+                    + "the minimum number " + nodeThresh + ". In safe mode "
+                    + "extension. Safe mode will be turned off automatically"));
+      }
     } else {
       int additional = (int) (total * 0.9990) - safe;
       assertTrue("Bad safemode status: '" + status + "'",
@@ -568,9 +577,9 @@ public class TestHASafeMode {
     assertTrue("Bad safemode status: '" + status + "'",
       status.startsWith(
         "Safe mode is ON. The reported blocks 10 has reached the threshold "
-        + "0.9990 of total blocks 10. The number of live datanodes 3 has "
-        + "reached the minimum number 0. In safe mode extension. "
-        + "Safe mode will be turned off automatically"));
+        + "0.9990 of total blocks 10. The minimum number of live datanodes is "
+        + "not required. In safe mode extension. Safe mode will be turned off "
+        + "automatically"));
 
     // Delete those blocks while the SBN is in safe mode.
     // Immediately roll the edit log before the actual deletions are sent