From e9a005dfcf4d2249235aeff4da85b321dddc1ca9 Mon Sep 17 00:00:00 2001
From: Wei-Chiu Chuang <weichiu@apache.org>
Date: Fri, 28 Dec 2018 10:34:18 -0800
Subject: [PATCH] HDFS-14171. Performance improvement in Tailing EditLog.
 Contributed by Kenneth Yang.

---
 .../hdfs/server/blockmanagement/BlockManagerSafeMode.java  | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManagerSafeMode.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManagerSafeMode.java
index 5a981e96af..1d7e69bacc 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManagerSafeMode.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManagerSafeMode.java
@@ -567,7 +567,12 @@ private void initializeReplQueuesIfNecessary() {
    */
   private boolean areThresholdsMet() {
     assert namesystem.hasWriteLock();
-    int datanodeNum = blockManager.getDatanodeManager().getNumLiveDataNodes();
+    // Calculating the number of live datanodes is time-consuming
+    // in large clusters. Skip it when datanodeThreshold is zero.
+    int datanodeNum = 0;
+    if (datanodeThreshold > 0) {
+      datanodeNum = blockManager.getDatanodeManager().getNumLiveDataNodes();
+    }
     synchronized (this) {
       return blockSafe >= blockThreshold && datanodeNum >= datanodeThreshold;
     }