[dual sampling] introduced option to disable dual sampling

agent/agent.go

@@ -176,15 +176,25 @@ func (a *Agent) Process(t model.Trace) {
 
 	var samplers []*Sampler
 	priority, ok := root.Metrics[samplingPriorityKey]
-	if priority == 0 {
-		// Use score engine for traces with no priority or priority set to 0
-		samplers = append(samplers, a.ScoreEngine)
-	}
-	if a.PriorityEngine != nil && ok {
-		// If Priority is defined, send to priority sampling, regardless of priority value.
-		// The sampler will keep or discard the trace, but we send everything so that it
-		// gets the big picture and can set the sampling rates accordingly.
-		samplers = append(samplers, a.PriorityEngine)
+	if a.conf.ScorePriority0Traces {
+		// Send traces to possibly several score engines.
+		if priority == 0 {
+			// Use score engine for traces with no priority or priority set to 0
+			samplers = append(samplers, a.ScoreEngine)
+		}
+		if a.PriorityEngine != nil && ok {
+			// If Priority is defined, send to priority sampling, regardless of priority value.
+			// The sampler will keep or discard the trace, but we send everything so that it
+			// gets the big picture and can set the sampling rates accordingly.
+			samplers = append(samplers, a.PriorityEngine)
+		}
+	} else {
+		// Send traces to one single engine, either Priority or Score
+		if ok {
+			samplers = []*Sampler{a.PriorityEngine}
+		} else {
+			samplers = []*Sampler{a.ScoreEngine}
+		}
 	}
 
 	priorityPtr := &ts.TracesPriorityNone

config/agent.go

@@ -38,10 +38,11 @@ type AgentConfig struct {
 	ExtraAggregators []string
 
 	// Sampler configuration
-	ExtraSampleRate  float64
-	PreSampleRate    float64
-	MaxTPS           float64
-	PrioritySampling bool
+	ExtraSampleRate      float64
+	PreSampleRate        float64
+	MaxTPS               float64
+	PrioritySampling     bool
+	ScorePriority0Traces bool
 
 	// Receiver
 	ReceiverHost    string
@@ -171,10 +172,11 @@ func NewDefaultAgentConfig() *AgentConfig {
 		BucketInterval:   time.Duration(10) * time.Second,
 		ExtraAggregators: []string{"http.status_code"},
 
-		ExtraSampleRate:  1.0,
-		PreSampleRate:    1.0,
-		MaxTPS:           10,
-		PrioritySampling: true,
+		ExtraSampleRate:      1.0,
+		PreSampleRate:        1.0,
+		MaxTPS:               10,
+		PrioritySampling:     true,
+		ScorePriority0Traces: true,
 
 		ReceiverHost:    "localhost",
 		ReceiverPort:    8126,
@@ -324,8 +326,11 @@ APM_CONF:
 	if v, e := conf.GetFloat("trace.sampler", "max_traces_per_second"); e == nil {
 		c.MaxTPS = v
 	}
-	if v := strings.ToLower(conf.GetDefault("trace.sampler", "priority_sampling", "")); v == "yes" || v == "true" {
-		c.PrioritySampling = true
+	if v := strings.ToLower(conf.GetDefault("trace.sampler", "priority_sampling", "yes")); v != "yes" && v != "true" {
+		c.PrioritySampling = false
+	}
+	if v := strings.ToLower(conf.GetDefault("trace.sampler", "score_priority_0_traces", "yes")); v != "yes" && v != "true" {
+		c.ScorePriority0Traces = false
 	}
 
 	if v, e := conf.GetInt("trace.receiver", "receiver_port"); e == nil {

config/agent_test.go

@@ -0,0 +1,41 @@
+package config
+
+import (
+	"strings"
+
+	"github.com/stretchr/testify/assert"
+
+	"testing"
+
+	"github.com/go-ini/ini"
+)
+
+func TestPrioritySamplerConfig(t *testing.T) {
+	assert := assert.New(t)
+	agentConfig := NewDefaultAgentConfig()
+
+	assert.True(agentConfig.PrioritySampling)
+	assert.True(agentConfig.ScorePriority0Traces)
+
+	dd, _ := ini.Load([]byte(strings.Join([]string{
+		"[trace.sampler]",
+	}, "\n")))
+
+	conf := &File{instance: dd, Path: "whatever"}
+	agentConfig, _ = NewAgentConfig(conf, nil)
+
+	assert.True(agentConfig.PrioritySampling)
+	assert.True(agentConfig.ScorePriority0Traces)
+
+	dd, _ = ini.Load([]byte(strings.Join([]string{
+		"[trace.sampler]",
+		"priority_sampling = no",
+		"score_priority_0_traces = no",
+	}, "\n")))
+
+	conf = &File{instance: dd, Path: "whatever"}
+	agentConfig, _ = NewAgentConfig(conf, nil)
+
+	assert.False(agentConfig.PrioritySampling)
+	assert.False(agentConfig.ScorePriority0Traces)
+}