introduce a samler fast path

DataDog · Dec 24, 2018 · 1730727 · 1730727
1 parent dce65e5
commit 1730727
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Showing 3 changed files with 7 additions and 4 deletions.
diff --git a/ddtrace/tracer/sampler.go b/ddtrace/tracer/sampler.go
@@ -62,6 +62,10 @@ const knuthFactor = uint64(1111111111111111111)
 
 // Sample returns true if the given span should be sampled.
 func (r *rateSampler) Sample(spn ddtrace.Span) bool {
+	if r.rate == 1 {
+		// fast path
+		return true
+	}
 	s, ok := spn.(*span)
 	if !ok {
 		return false

diff --git a/ddtrace/tracer/sampler_test.go b/ddtrace/tracer/sampler_test.go
@@ -164,7 +164,7 @@ func TestRateSampler(t *testing.T) {
 	assert.True(NewRateSampler(1).Sample(newBasicSpan("test")))
 	assert.False(NewRateSampler(0).Sample(newBasicSpan("test")))
 	assert.False(NewRateSampler(0).Sample(newBasicSpan("test")))
-	assert.False(NewRateSampler(1).Sample(internal.NoopSpan{}))
+	assert.False(NewRateSampler(0.99).Sample(internal.NoopSpan{}))
 }
 
 func TestRateSamplerSetting(t *testing.T) {

diff --git a/ddtrace/tracer/tracer.go b/ddtrace/tracer/tracer.go
@@ -366,9 +366,8 @@ func (t *tracer) sample(span *span) {
 		return
 	}
 	sampler := t.config.sampler
-	sampled := sampler.Sample(span)
-	span.context.drop = !sampled
-	if !sampled {
+	if !sampler.Sample(span) {
+		span.context.drop = true
 		return
 	}
 	if rs, ok := sampler.(RateSampler); ok && rs.Rate() < 1 {