AMBARI-19947. To make sure LLAP preemption happens correctly, should enable priority-utilization.underutilized-preemption.enabled=true when YARN preemption is enabled.(vbrodetskyi)

ambari-server/src/main/resources/stacks/HDP/2.6/services/YARN/configuration/yarn-site.xml

@@ -23,4 +23,16 @@
     <description>When HA is enabled, the class to be used by Clients, AMs and NMs to failover to the Active RM. It should extend org.apache.hadoop.yarn.client.RMFailoverProxyProvider</description>
     <on-ambari-upgrade add="false"/>
   </property>
+  <property>
+    <name>yarn.scheduler.capacity.ordering-policy.priority-utilization.underutilized-preemption.enabled</name>
+    <value>false</value>
+    <description>This property need to be set to make preemption can happen under a fragmented cluster.</description>
+    <depends-on>
+      <property>
+        <type>yarn-site</type>
+        <name>yarn.resourcemanager.scheduler.monitor.enable</name>
+      </property>
+    </depends-on>
+    <on-ambari-upgrade add="false"/>
+  </property>
 </configuration>

ambari-server/src/main/resources/stacks/HDP/2.6/services/stack_advisor.py

@@ -138,6 +138,18 @@ class HDP26StackAdvisor(HDP25StackAdvisor):
         elif superset_database_type == "postgresql":
             putSupersetProperty("SUPERSET_DATABASE_PORT", "5432")
 
+  def recommendYARNConfigurations(self, configurations, clusterData, services, hosts):
+    super(HDP26StackAdvisor, self).recommendYARNConfigurations(configurations, clusterData, services, hosts)
+    putYarnSiteProperty = self.putProperty(configurations, "yarn-site", services)
+
+    if "yarn-site" in services["configurations"] and \
+                    "yarn.resourcemanager.scheduler.monitor.enable" in services["configurations"]["yarn-site"]["properties"]:
+      scheduler_monitor_enabled = services["configurations"]["yarn-site"]["properties"]["yarn.resourcemanager.scheduler.monitor.enable"]
+      if scheduler_monitor_enabled.lower() == 'true':
+        putYarnSiteProperty('yarn.scheduler.capacity.ordering-policy.priority-utilization.underutilized-preemption.enabled', "true")
+      else:
+        putYarnSiteProperty('yarn.scheduler.capacity.ordering-policy.priority-utilization.underutilized-preemption.enabled', "false")
+
   def getMetadataConnectionString(self, database_type):
       driverDict = {
           'mysql': 'jdbc:mysql://{0}:{2}/{1}?createDatabaseIfNotExist=true',