YARN-9013. Fix CheckStyle.

Author: slfan1989

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/conf/YarnConfiguration.java

@@ -4267,7 +4267,7 @@ public static boolean isAclEnabled(Configuration conf) {
    */
   public static final String ROUTER_CLIENTRM_SUBMIT_RETRY =
       ROUTER_PREFIX + "submit.retry";
-  public static final int DEFAULT_ROUTER_CLIENTRM_SUBMIT_RETRY = 3;
+  public static final int DEFAULT_ROUTER_CLIENTRM_SUBMIT_RETRY = 1;
 
   /**
    * GetNewApplication and SubmitApplication request retry interval time.
@@ -4367,7 +4367,7 @@ public static boolean isAclEnabled(Configuration conf) {
    * the default value is 0s.
    */
   public static final long DEFAULT_ROUTER_USER_CLIENT_THREAD_POOL_KEEP_ALIVE_TIME =
-      TimeUnit.SECONDS.toMillis(0); // 0s
+      TimeUnit.SECONDS.toMillis(30); // 0s
 
   /** The address of the Router web application. */
   public static final String ROUTER_WEBAPP_ADDRESS =

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/resources/yarn-default.xml

@@ -5132,10 +5132,10 @@
 
   <property>
     <name>yarn.router.interceptor.user-thread-pool.keep-alive-time</name>
-    <value>0s</value>
+    <value>30s</value>
     <description>
       This configurable is used to set the keepAliveTime of the thread pool of the interceptor.
-      Default is 0s.
+      Default is 30s.
     </description>
   </property>
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-globalpolicygenerator/src/main/java/org/apache/hadoop/yarn/server/globalpolicygenerator/applicationcleaner/ApplicationCleaner.java

@@ -19,7 +19,6 @@
 package org.apache.hadoop.yarn.server.globalpolicygenerator.applicationcleaner;
 
 import java.util.HashSet;
-import java.util.List;
 import java.util.Set;
 
 import org.apache.commons.lang3.time.DurationFormatUtils;