producer: increase performance of sampling rate lookup (#264)

Formatting a string with version and domain when looking up sampling
rate hurts performance. Instead, use a dedicated structure for key. It
also reduces the pressure on the GC.

producer/proto/producer_nf.go

@@ -18,16 +18,19 @@ type SamplingRateSystem interface {
 	AddSamplingRate(version uint16, obsDomainId uint32, samplingRate uint32)
 }
 
+type basicSamplingRateKey struct {
+	version     uint16
+	obsDomainId uint32
+}
+
 type basicSamplingRateSystem struct {
-	//sampling     map[uint16]map[uint32]uint32
-	sampling     map[string]uint32
+	sampling     map[basicSamplingRateKey]uint32
 	samplinglock *sync.RWMutex
 }
 
 func CreateSamplingSystem() SamplingRateSystem {
 	ts := &basicSamplingRateSystem{
-		//sampling:     make(map[uint16]map[uint32]uint32),
-		sampling:     make(map[string]uint32),
+		sampling:     make(map[basicSamplingRateKey]uint32),
 		samplinglock: &sync.RWMutex{},
 	}
 	return ts
@@ -36,18 +39,19 @@ func CreateSamplingSystem() SamplingRateSystem {
 func (s *basicSamplingRateSystem) AddSamplingRate(version uint16, obsDomainId uint32, samplingRate uint32) {
 	s.samplinglock.Lock()
 	defer s.samplinglock.Unlock()
-	/*_, exists := s.sampling[version]
-	if exists != true {
-		s.sampling[version] = make(map[uint32]uint32)
-	}
-	s.sampling[version][obsDomainId] = samplingRate*/
-	s.sampling[fmt.Sprintf("%d-%d", version, obsDomainId)] = samplingRate
+	s.sampling[basicSamplingRateKey{
+		version:     version,
+		obsDomainId: obsDomainId,
+	}] = samplingRate
 }
 
 func (s *basicSamplingRateSystem) GetSamplingRate(version uint16, obsDomainId uint32) (uint32, error) {
 	s.samplinglock.RLock()
 	defer s.samplinglock.RUnlock()
-	if samplingRate, ok := s.sampling[fmt.Sprintf("%d-%d", version, obsDomainId)]; ok {
+	if samplingRate, ok := s.sampling[basicSamplingRateKey{
+		version:     version,
+		obsDomainId: obsDomainId,
+	}]; ok {
 		return samplingRate, nil
 	}