aggregator: don't allocate memory if we don't have tags

Before:
BenchmarkGetContextNoTags-10    	39929401	        29.70 ns/op	      16 B/op	       1 allocs/op

After:
BenchmarkGetContextNoTags-10    	419886585	         2.902 ns/op	       0 B/op	       0 allocs/op

This might look not much, but this makes a lot of difference in term of allocation
when a counter is called repeatedly inside a loop.

statsd/aggregator.go

@@ -172,14 +172,22 @@ func (a *aggregator) flushMetrics() []metric {
 	return metrics
 }
 
+// getContext returns the context for a metric name and tags.
+//
+// The context is the metric name and tags separated by a separator symbol.
+// It is not intended to be used as a metric name but as a unique key to aggregate
 func getContext(name string, tags []string) string {
 	c, _ := getContextAndTags(name, tags)
 	return c
 }
 
+// getContextAndTags returns the context and tags for a metric name and tags.
+//
+// See getContext for usage for context
+// The tags are the tags separated by a separator symbol and can be re-used to pass down to the writer
 func getContextAndTags(name string, tags []string) (string, string) {
 	if len(tags) == 0 {
-		return name + nameSeparatorSymbol, ""
+		return name, ""
 	}
 	n := len(name) + len(nameSeparatorSymbol) + len(tagSeparatorSymbol)*(len(tags)-1)
 	for _, s := range tags {

statsd/aggregator_test.go

@@ -377,7 +377,7 @@ func TestGetContextAndTags(t *testing.T) {
 			testName:    "no tags",
 			name:        "name",
 			tags:        nil,
-			wantContext: "name:",
+			wantContext: "name",
 			wantTags:    "",
 		},
 		{
@@ -403,3 +403,21 @@ func TestGetContextAndTags(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkGetContext(b *testing.B) {
+	name := "test.metric"
+	tags := []string{"tag:tag", "foo:bar"}
+	for i := 0; i < b.N; i++ {
+		getContext(name, tags)
+	}
+	b.ReportAllocs()
+}
+
+func BenchmarkGetContextNoTags(b *testing.B) {
+	name := "test.metric"
+	var tags []string
+	for i := 0; i < b.N; i++ {
+		getContext(name, tags)
+	}
+	b.ReportAllocs()
+}

statsd/statsd_benchmark_test.go

@@ -26,7 +26,15 @@ func setupUDSClientServer(b *testing.B, options []statsd.Option) (*statsd.Client
 	}
 	go func() {
 		for {
-			_, err := conn.Accept()
+			c, err := conn.Accept()
+			// We need to read everything from the socket to avoid blocking the sender
+			buf := make([]byte, 1024)
+			for {
+				_, err = c.Read(buf)
+				if err != nil {
+					break
+				}
+			}
 			if err != nil {
 				return
 			}
@@ -76,8 +84,9 @@ func benchmarkStatsdDifferentMetrics(b *testing.B, transport string, extraOption
 	b.RunParallel(func(pb *testing.PB) {
 		testNumber := atomic.AddInt32(&n, 1)
 		name := fmt.Sprintf("test.metric%d", testNumber)
+		tags := []string{"tag:tag"}
 		for pb.Next() {
-			client.Gauge(name, 1, []string{"tag:tag"}, 1)
+			client.Gauge(name, 1, tags, 1)
 		}
 	})
 	client.Flush()
@@ -96,7 +105,8 @@ func benchmarkStatsdSameMetrics(b *testing.B, transport string, extraOptions ...
 
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
-			client.Gauge("test.metric", 1, []string{"tag:tag"}, 1)
+			tags := []string{"tag:tag"}
+			client.Gauge("test.metric", 1, tags, 1)
 		}
 	})
 	client.Flush()