HADOOP-11714. Add more trace log4j messages to SpanReceiverHost (cmccabe)

(cherry picked from commit bf3275dbaa99105d49520e25f5a6eadd6fd5b7ed)
(cherry picked from commit eb4eb63de3b929d154360e20abb895f0e14134cf)

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -236,6 +236,8 @@ Release 2.7.0 - UNRELEASED
     HADOOP-8059. Add javadoc to InterfaceAudience and InterfaceStability.
     (Brandon Li via suresh)
 
+    HADOOP-11714. Add more trace log4j messages to SpanReceiverHost (cmccabe)
+
   OPTIMIZATIONS
 
     HADOOP-11323. WritableComparator#compare keeps reference to byte array.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/tracing/SpanReceiverHost.java

@@ -134,20 +134,27 @@ public class SpanReceiverHost implements TraceAdminProtocol {
     String[] receiverNames =
         config.getTrimmedStrings(SPAN_RECEIVERS_CONF_KEY);
     if (receiverNames == null || receiverNames.length == 0) {
+      if (LOG.isTraceEnabled()) {
+        LOG.trace("No span receiver names found in " +
+                  SPAN_RECEIVERS_CONF_KEY + ".");
+      }
       return;
     }
     // It's convenient to have each daemon log to a random trace file when
     // testing.
     if (config.get(LOCAL_FILE_SPAN_RECEIVER_PATH) == null) {
-      config.set(LOCAL_FILE_SPAN_RECEIVER_PATH,
-          getUniqueLocalTraceFileName());
+      String uniqueFile = getUniqueLocalTraceFileName();
+      config.set(LOCAL_FILE_SPAN_RECEIVER_PATH, uniqueFile);
+      if (LOG.isTraceEnabled()) {
+        LOG.trace("Set " + LOCAL_FILE_SPAN_RECEIVER_PATH + " to " +  uniqueFile);
+      }
     }
     for (String className : receiverNames) {
       try {
         SpanReceiver rcvr = loadInstance(className, EMPTY);
         Trace.addReceiver(rcvr);
         receivers.put(highestId++, rcvr);
-        LOG.info("SpanReceiver " + className + " was loaded successfully.");
+        LOG.info("Loaded SpanReceiver " + className + " successfully.");
       } catch (IOException e) {
         LOG.error("Failed to load SpanReceiver", e);
       }