trace: Use non-generic to replace newEvictedQueue in trace.start to reduce memory usage. (#5497)

benchstat:
```
goos: darwin
goarch: arm64
pkg: go.opentelemetry.io/otel/sdk/trace
              │     old     │                 new                 │
              │   sec/op    │   sec/op     vs base                │
TraceStart-10   950.6n ± 1%   641.0n ± 0%  -32.57% (p=0.000 n=10)

              │     old     │                new                 │
              │    B/op     │    B/op     vs base                │
TraceStart-10   1040.0 ± 0%   704.0 ± 0%  -32.31% (p=0.000 n=10)

              │    old     │                new                 │
              │ allocs/op  │ allocs/op   vs base                │
TraceStart-10   20.00 ± 0%   14.00 ± 0%  -30.00% (p=0.000 n=10)
```

---------

Co-authored-by: Damien Mathieu <damien.mathieu@elastic.co>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -27,6 +27,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   - The exporter no longer exports the deprecated "otel.library.name" or "otel.library.version" attributes.
 - Upgrade `go.opentelemetry.io/otel/semconv/v1.25.0` to `go.opentelemetry.io/otel/semconv/v1.26.0` in `go.opentelemetry.io/otel/sdk/resource`. (#5490)
 - Upgrade `go.opentelemetry.io/otel/semconv/v1.25.0` to `go.opentelemetry.io/otel/semconv/v1.26.0` in `go.opentelemetry.io/otel/sdk/trace`. (#5490)
+- Use non-generic functions in the `Start` method of `"go.opentelemetry.io/otel/sdk/trace".Trace` to reduce memory allocation. (#5497)
 
 ### Fixed
 

sdk/trace/evictedqueue.go

@@ -4,7 +4,6 @@
 package trace // import "go.opentelemetry.io/otel/sdk/trace"
 
 import (
-	"fmt"
 	"slices"
 	"sync"
 
@@ -19,13 +18,19 @@ type evictedQueue[T any] struct {
 	logDropped   func()
 }
 
-func newEvictedQueue[T any](capacity int) evictedQueue[T] {
-	var tVal T
-	msg := fmt.Sprintf("limit reached: dropping trace %T", tVal)
+func newEvictedQueueEvent(capacity int) evictedQueue[Event] {
 	// Do not pre-allocate queue, do this lazily.
-	return evictedQueue[T]{
+	return evictedQueue[Event]{
 		capacity:   capacity,
-		logDropped: sync.OnceFunc(func() { global.Warn(msg) }),
+		logDropped: sync.OnceFunc(func() { global.Warn("limit reached: dropping trace trace.Event") }),
+	}
+}
+
+func newEvictedQueueLink(capacity int) evictedQueue[Link] {
+	// Do not pre-allocate queue, do this lazily.
+	return evictedQueue[Link]{
+		capacity:   capacity,
+		logDropped: sync.OnceFunc(func() { global.Warn("limit reached: dropping trace trace.Link") }),
 	}
 }
 

sdk/trace/evictedqueue_test.go

@@ -14,47 +14,47 @@ func init() {
 }
 
 func TestAdd(t *testing.T) {
-	q := newEvictedQueue[string](3)
-	q.add("value1")
-	q.add("value2")
+	q := newEvictedQueueLink(3)
+	q.add(Link{})
+	q.add(Link{})
 	if wantLen, gotLen := 2, len(q.queue); wantLen != gotLen {
 		t.Errorf("got queue length %d want %d", gotLen, wantLen)
 	}
 }
 
 func TestCopy(t *testing.T) {
-	q := newEvictedQueue[string](3)
-	q.add("value1")
+	q := newEvictedQueueEvent(3)
+	q.add(Event{Name: "value1"})
 	cp := q.copy()
 
-	q.add("value2")
-	assert.Equal(t, []string{"value1"}, cp, "queue update modified copy")
+	q.add(Event{Name: "value2"})
+	assert.Equal(t, []Event{{Name: "value1"}}, cp, "queue update modified copy")
 
-	cp[0] = "value0"
-	assert.Equal(t, "value1", q.queue[0], "copy update modified queue")
+	cp[0] = Event{Name: "value0"}
+	assert.Equal(t, Event{Name: "value1"}, q.queue[0], "copy update modified queue")
 }
 
 func TestDropCount(t *testing.T) {
-	q := newEvictedQueue[string](3)
+	q := newEvictedQueueEvent(3)
 	var called bool
 	q.logDropped = func() { called = true }
 
-	q.add("value1")
+	q.add(Event{Name: "value1"})
 	assert.False(t, called, `"value1" logged as dropped`)
-	q.add("value2")
+	q.add(Event{Name: "value2"})
 	assert.False(t, called, `"value2" logged as dropped`)
-	q.add("value3")
+	q.add(Event{Name: "value3"})
 	assert.False(t, called, `"value3" logged as dropped`)
-	q.add("value1")
+	q.add(Event{Name: "value1"})
 	assert.True(t, called, `"value2" not logged as dropped`)
-	q.add("value4")
+	q.add(Event{Name: "value4"})
 	if wantLen, gotLen := 3, len(q.queue); wantLen != gotLen {
 		t.Errorf("got queue length %d want %d", gotLen, wantLen)
 	}
 	if wantDropCount, gotDropCount := 2, q.droppedCount; wantDropCount != gotDropCount {
 		t.Errorf("got drop count %d want %d", gotDropCount, wantDropCount)
 	}
-	wantArr := []string{"value3", "value1", "value4"}
+	wantArr := []Event{{Name: "value3"}, {Name: "value1"}, {Name: "value4"}}
 	gotArr := q.copy()
 
 	if wantLen, gotLen := len(wantArr), len(gotArr); gotLen != wantLen {

sdk/trace/trace_test.go

@@ -2107,3 +2107,16 @@ func TestAddLinkToNonRecordingSpan(t *testing.T) {
 		t.Errorf("AddLinkToNonRecordingSpan: -got +want %s", diff)
 	}
 }
+
+func BenchmarkTraceStart(b *testing.B) {
+	tracer := NewTracerProvider().Tracer("")
+	ctx := trace.ContextWithSpanContext(context.Background(), trace.SpanContext{})
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		_, span := tracer.Start(ctx, "")
+		span.End()
+	}
+}

sdk/trace/tracer.go

@@ -132,8 +132,8 @@ func (tr *tracer) newRecordingSpan(psc, sc trace.SpanContext, name string, sr Sa
 		spanKind:    trace.ValidateSpanKind(config.SpanKind()),
 		name:        name,
 		startTime:   startTime,
-		events:      newEvictedQueue[Event](tr.provider.spanLimits.EventCountLimit),
-		links:       newEvictedQueue[Link](tr.provider.spanLimits.LinkCountLimit),
+		events:      newEvictedQueueEvent(tr.provider.spanLimits.EventCountLimit),
+		links:       newEvictedQueueLink(tr.provider.spanLimits.LinkCountLimit),
 		tracer:      tr,
 	}