Performance improvements for recordingSpan SetAttributes and addOverCapAttrs (#5864)

Good day,

While working on
https://github.com/open-telemetry/opentelemetry-go/pull/5858 I found
some other possible improvements.

This PR:
- Adds an early return to `SetAttributes` when no attributes are
provided.
- Only increases `s.attributes` to guarantee that there is enough space
for elements to be added.
- Fixes and issue where `truncateAttr` was not used when a attribute was
being updated in `addOverCapAttrs`.

Thanks for reviewing and please let me know if any changes are needed.

---------

Co-authored-by: Damien Mathieu <42@dmathieu.com>

CHANGELOG.md

@@ -18,6 +18,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - `Logger.Enabled` in `go.opentelemetry.io/otel/log` now accepts a newly introduced `EnabledParameters` type instead of `Record`. (#5791)
 - `FilterProcessor.Enabled` in `go.opentelemetry.io/otel/sdk/log/internal/x` now accepts `EnabledParameters` instead of `Record`. (#5791)
 - The `Record` type in `go.opentelemetry.io/otel/log` is no longer comparable. (#5847)
+- Performance improvements for the trace SDK `SetAttributes` method in `Span`. (#5864)
 
 ### Deprecated
 

sdk/trace/span.go

@@ -174,6 +174,16 @@ func (s *recordingSpan) IsRecording() bool {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
+	return s.isRecording()
+}
+
+// isRecording returns if this span is being recorded. If this span has ended
+// this will return false.
+// This is done without acquiring a lock.
+func (s *recordingSpan) isRecording() bool {
+	if s == nil {
+		return false
+	}
 	return s.endTime.IsZero()
 }
 
@@ -182,11 +192,15 @@ func (s *recordingSpan) IsRecording() bool {
 // included in the set status when the code is for an error. If this span is
 // not being recorded than this method does nothing.
 func (s *recordingSpan) SetStatus(code codes.Code, description string) {
-	if !s.IsRecording() {
+	if s == nil {
 		return
 	}
+
 	s.mu.Lock()
 	defer s.mu.Unlock()
+	if !s.isRecording() {
+		return
+	}
 	if s.status.Code > code {
 		return
 	}
@@ -210,12 +224,15 @@ func (s *recordingSpan) SetStatus(code codes.Code, description string) {
 // attributes the span is configured to have, the last added attributes will
 // be dropped.
 func (s *recordingSpan) SetAttributes(attributes ...attribute.KeyValue) {
-	if !s.IsRecording() {
+	if s == nil || len(attributes) == 0 {
 		return
 	}
 
 	s.mu.Lock()
 	defer s.mu.Unlock()
+	if !s.isRecording() {
+		return
+	}
 
 	limit := s.tracer.provider.spanLimits.AttributeCountLimit
 	if limit == 0 {
@@ -233,7 +250,7 @@ func (s *recordingSpan) SetAttributes(attributes ...attribute.KeyValue) {
 
 	// Otherwise, add without deduplication. When attributes are read they
 	// will be deduplicated, optimizing the operation.
-	s.attributes = slices.Grow(s.attributes, len(s.attributes)+len(attributes))
+	s.attributes = slices.Grow(s.attributes, len(attributes))
 	for _, a := range attributes {
 		if !a.Valid() {
 			// Drop all invalid attributes.
@@ -280,13 +297,17 @@ func (s *recordingSpan) addOverCapAttrs(limit int, attrs []attribute.KeyValue) {
 
 	// Do not set a capacity when creating this map. Benchmark testing has
 	// showed this to only add unused memory allocations in general use.
-	exists := make(map[attribute.Key]int)
+	exists := make(map[attribute.Key]int, len(s.attributes))
-	s.dedupeAttrsFromRecord(&exists)
+	s.dedupeAttrsFromRecord(exists)
 
 	// Now that s.attributes is deduplicated, adding unique attributes up to
 	// the capacity of s will not over allocate s.attributes.
-	sum := len(attrs) + len(s.attributes)
+
-	s.attributes = slices.Grow(s.attributes, min(sum, limit))
+	// max size = limit
+	maxCap := min(len(attrs)+len(s.attributes), limit)
+	if cap(s.attributes) < maxCap {
+		s.attributes = slices.Grow(s.attributes, maxCap-cap(s.attributes))
+	}
 	for _, a := range attrs {
 		if !a.Valid() {
 			// Drop all invalid attributes.
@@ -296,6 +317,7 @@ func (s *recordingSpan) addOverCapAttrs(limit int, attrs []attribute.KeyValue) {
 
 		if idx, ok := exists[a.Key]; ok {
 			// Perform all updates before dropping, even when at capacity.
+			a = truncateAttr(s.tracer.provider.spanLimits.AttributeValueLengthLimit, a)
 			s.attributes[idx] = a
 			continue
 		}
@@ -518,12 +540,15 @@ func (s *recordingSpan) addEvent(name string, o ...trace.EventOption) {
 // SetName sets the name of this span. If this span is not being recorded than
 // this method does nothing.
 func (s *recordingSpan) SetName(name string) {
-	if !s.IsRecording() {
+	if s == nil {
 		return
 	}
 
 	s.mu.Lock()
 	defer s.mu.Unlock()
+	if !s.isRecording() {
+		return
+	}
 	s.name = name
 }
 
@@ -579,23 +604,23 @@ func (s *recordingSpan) Attributes() []attribute.KeyValue {
 func (s *recordingSpan) dedupeAttrs() {
 	// Do not set a capacity when creating this map. Benchmark testing has
 	// showed this to only add unused memory allocations in general use.
-	exists := make(map[attribute.Key]int)
+	exists := make(map[attribute.Key]int, len(s.attributes))
-	s.dedupeAttrsFromRecord(&exists)
+	s.dedupeAttrsFromRecord(exists)
 }
 
 // dedupeAttrsFromRecord deduplicates the attributes of s to fit capacity
 // using record as the record of unique attribute keys to their index.
 //
 // This method assumes s.mu.Lock is held by the caller.
-func (s *recordingSpan) dedupeAttrsFromRecord(record *map[attribute.Key]int) {
+func (s *recordingSpan) dedupeAttrsFromRecord(record map[attribute.Key]int) {
 	// Use the fact that slices share the same backing array.
 	unique := s.attributes[:0]
 	for _, a := range s.attributes {
-		if idx, ok := (*record)[a.Key]; ok {
+		if idx, ok := record[a.Key]; ok {
 			unique[idx] = a
 		} else {
 			unique = append(unique, a)
-			(*record)[a.Key] = len(unique) - 1
+			record[a.Key] = len(unique) - 1
 		}
 	}
 	// s.attributes have element types of attribute.KeyValue. These types are
@@ -755,12 +780,16 @@ func (s *recordingSpan) snapshot() ReadOnlySpan {
 }
 
 func (s *recordingSpan) addChild() {
-	if !s.IsRecording() {
+	if s == nil {
 		return
 	}
+
 	s.mu.Lock()
+	defer s.mu.Unlock()
+	if !s.isRecording() {
+		return
+	}
 	s.childSpanCount++
-	s.mu.Unlock()
 }
 
 func (*recordingSpan) private() {}