Add support for timing sums in statsd input (#3234)

plugins/inputs/statsd/running_stats.go

@@ -24,8 +24,10 @@ type RunningStats struct {
 	perc      []float64
 	PercLimit int
 
-	upper float64
+	sum float64
+
 	lower float64
+	upper float64
 
 	// cache if we have sorted the list so that we never re-sort a sorted list,
 	// which can have very bad performance.
@@ -51,6 +53,9 @@ func (rs *RunningStats) AddValue(v float64) {
 	rs.ex += v - rs.k
 	rs.ex2 += (v - rs.k) * (v - rs.k)
 
+	// add to running sum
+	rs.sum += v
+
 	// track upper and lower bounds
 	if v > rs.upper {
 		rs.upper = v
@@ -78,6 +83,10 @@ func (rs *RunningStats) Stddev() float64 {
 	return math.Sqrt(rs.Variance())
 }
 
+func (rs *RunningStats) Sum() float64 {
+	return rs.sum
+}
+
 func (rs *RunningStats) Upper() float64 {
 	return rs.upper
 }