Emit metric to count unique traces (root spans) (#574)

flusher.go

@@ -434,7 +434,9 @@ func (s *Server) flushTraces(ctx context.Context) {
 		}
 
 		spansReceivedTotal := atomic.SwapInt64(&value.ssfSpansReceivedTotal, 0)
+		spansRootReceivedTotal := atomic.SwapInt64(&value.ssfRootSpansReceivedTotal, 0)
 		s.Statsd.Count("ssf.spans.received_total", spansReceivedTotal, tags, 1.0)
+		s.Statsd.Count("ssf.spans.root.received_total", spansRootReceivedTotal, append(tags, "veneurglobalonly:true"), 1.0)
 		return true
 	})
 

server.go

@@ -142,7 +142,8 @@ type Server struct {
 // It is expected the values on the struct will only be handled
 // using atomic operations
 type ssfServiceSpanMetrics struct {
-	ssfSpansReceivedTotal int64
+	ssfSpansReceivedTotal     int64
+	ssfRootSpansReceivedTotal int64
 }
 
 // SetLogger sets the default logger in veneur to the passed value.
@@ -834,6 +835,10 @@ func (s *Server) handleSSF(span *ssf.SSFSpan, ssfFormat string) {
 
 	atomic.AddInt64(&metricsStruct.ssfSpansReceivedTotal, 1)
 
+	if span.Id == span.TraceId {
+		atomic.AddInt64(&metricsStruct.ssfRootSpansReceivedTotal, 1)
+	}
+
 	s.SpanChan <- span
 }