Support for root logger level runtime update

Closes: #2517

src/main/java/org/elasticsearch/common/logging/ESLoggerFactory.java

@@ -66,9 +66,15 @@ public abstract class ESLoggerFactory {
         return defaultFactory.newInstance(name.intern());
     }
 
+    public static ESLogger getRootLogger() {
+        return defaultFactory.rootLogger();
+    }
+
     public ESLogger newInstance(String name) {
         return newInstance(null, name);
     }
 
+    protected abstract ESLogger rootLogger();
+
     protected abstract ESLogger newInstance(String prefix, String name);
 }

src/main/java/org/elasticsearch/common/logging/jdk/JdkESLoggerFactory.java

@@ -22,11 +22,18 @@ package org.elasticsearch.common.logging.jdk;
 import org.elasticsearch.common.logging.ESLogger;
 import org.elasticsearch.common.logging.ESLoggerFactory;
 
+import java.util.logging.LogManager;
+
 /**
  *
  */
 public class JdkESLoggerFactory extends ESLoggerFactory {
 
+    @Override
+    protected ESLogger rootLogger() {
+        return getLogger("");
+    }
+
     @Override
     protected ESLogger newInstance(String prefix, String name) {
         final java.util.logging.Logger logger = java.util.logging.Logger.getLogger(name);

src/main/java/org/elasticsearch/common/logging/log4j/Log4jESLoggerFactory.java

@@ -19,6 +19,8 @@
 
 package org.elasticsearch.common.logging.log4j;
 
+import org.apache.log4j.LogManager;
+import org.apache.log4j.Logger;
 import org.elasticsearch.common.logging.ESLogger;
 import org.elasticsearch.common.logging.ESLoggerFactory;
 
@@ -27,6 +29,11 @@ import org.elasticsearch.common.logging.ESLoggerFactory;
  */
 public class Log4jESLoggerFactory extends ESLoggerFactory {
 
+    @Override
+    protected ESLogger rootLogger() {
+        return new Log4jESLogger(null, Logger.getRootLogger());
+    }
+
     @Override
     protected ESLogger newInstance(String prefix, String name) {
         final org.apache.log4j.Logger logger = org.apache.log4j.Logger.getLogger(name);

src/main/java/org/elasticsearch/common/logging/slf4j/Slf4jESLoggerFactory.java

@@ -21,6 +21,7 @@ package org.elasticsearch.common.logging.slf4j;
 
 import org.elasticsearch.common.logging.ESLogger;
 import org.elasticsearch.common.logging.ESLoggerFactory;
+import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
@@ -28,6 +29,11 @@ import org.slf4j.LoggerFactory;
  */
 public class Slf4jESLoggerFactory extends ESLoggerFactory {
 
+    @Override
+    protected ESLogger rootLogger() {
+        return getLogger(Logger.ROOT_LOGGER_NAME);
+    }
+
     @Override
     protected ESLogger newInstance(String prefix, String name) {
         return new Slf4jESLogger(prefix, LoggerFactory.getLogger(name));

src/main/java/org/elasticsearch/node/settings/NodeSettingsService.java

@@ -79,7 +79,11 @@ public class NodeSettingsService extends AbstractComponent implements ClusterSta
             for (Map.Entry<String, String> entry : event.state().metaData().settings().getAsMap().entrySet()) {
                 if (entry.getKey().startsWith("logger.")) {
                     String component = entry.getKey().substring("logger.".length());
-                    ESLoggerFactory.getLogger(component).setLevel(entry.getValue());
+                    if ("_root".equals(component)) {
+                        ESLoggerFactory.getRootLogger().setLevel(entry.getValue());
+                    } else {
+                        ESLoggerFactory.getLogger(component).setLevel(entry.getValue());
+                    }
                 }
             }
         } catch (Exception e) {