Add additional logging to make spotting stats issues easier

server/src/main/java/org/elasticsearch/monitor/Probes.java

@@ -9,21 +9,29 @@
 
 package org.elasticsearch.monitor;
 
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
 import java.lang.management.OperatingSystemMXBean;
 import java.lang.reflect.Method;
 
 public class Probes {
+    private static final Logger logger = LogManager.getLogger(Probes.class);
+
     public static short getLoadAndScaleToPercent(Method method, OperatingSystemMXBean osMxBean) {
+        logger.debug("Starting probe of method {} on osMxBean {}", method, osMxBean);
         if (method != null) {
             try {
                 double load = (double) method.invoke(osMxBean);
                 if (load >= 0) {
                     return (short) (load * 100);
                 }
             } catch (Exception e) {
+                logger.info(() -> "failed to invoke method [" + method + "] on osMxBean [" + osMxBean + "]", e);
                 return -1;
             }
         }
+        logger.debug("Method is null. Returning default value.");
         return -1;
     }
 }