MAPREDUCE-6958. Shuffle audit logger should log size of shuffle transfer. Contributed by Jason Lowe

(cherry picked from commit b3d61304f2fa4a99526f7a60ccaac9f262083079)

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-shuffle/src/main/java/org/apache/hadoop/mapred/ShuffleHandler.java

@@ -992,13 +992,6 @@ public class ShuffleHandler extends AuxiliaryService {
         return;
       }
 
-      // this audit log is disabled by default,
-      // to turn it on please enable this audit log
-      // on log4j.properties by uncommenting the setting
-      if (AUDITLOG.isDebugEnabled()) {
-        AUDITLOG.debug("shuffle for " + jobQ.get(0) + " mappers: " + mapIds +
-                         " reducer " + reduceQ.get(0));
-      }
       int reduceId;
       String jobId;
       try {
@@ -1183,6 +1176,17 @@ public class ShuffleHandler extends AuxiliaryService {
 
       // Now set the response headers.
       setResponseHeaders(response, keepAliveParam, contentLength);
+
+      // this audit log is disabled by default,
+      // to turn it on please enable this audit log
+      // on log4j.properties by uncommenting the setting
+      if (AUDITLOG.isDebugEnabled()) {
+        StringBuilder sb = new StringBuilder("shuffle for ").append(jobId);
+        sb.append(" mappers: ").append(mapIds);
+        sb.append(" reducer ").append(reduce);
+        sb.append(" length ").append(contentLength);
+        AUDITLOG.debug(sb.toString());
+      }
     }
 
     protected void setResponseHeaders(HttpResponse response,