HDFS-15350. Set dfs.client.failover.random.order to true as default. (#2008)

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/client/HdfsClientConfigKeys.java

@@ -343,7 +343,7 @@ public interface HdfsClientConfigKeys {
         PREFIX + "connection.retries.on.timeouts";
     int     CONNECTION_RETRIES_ON_SOCKET_TIMEOUTS_DEFAULT = 0;
     String  RANDOM_ORDER = PREFIX + "random.order";
-    boolean RANDOM_ORDER_DEFAULT = false;
+    boolean RANDOM_ORDER_DEFAULT = true;
     String  RESOLVE_ADDRESS_NEEDED_KEY = PREFIX + "resolve-needed";
     boolean RESOLVE_ADDRESS_NEEDED_DEFAULT = false;
     String RESOLVE_SERVICE_KEY = PREFIX + "resolver.impl";

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

@@ -4070,7 +4070,7 @@
 
 <property>
   <name>dfs.client.failover.random.order</name>
-  <value>false</value>
+  <value>true</value>
   <description>
     Determines if the failover proxies are picked in random order instead of the
     configured order. Random order may be enabled for better load balancing

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

@@ -78,6 +78,7 @@ public class TestObserverReadProxyProvider {
     // transition observer back and forth
     conf.setTimeDuration(
         OBSERVER_PROBE_RETRY_PERIOD_KEY, 0, TimeUnit.MILLISECONDS);
+    conf.setBoolean(HdfsClientConfigKeys.Failover.RANDOM_ORDER, false);
   }
 
   private void setupProxyProvider(int namenodeCount) throws Exception {