Performance improvements for recordingSpan SetAttributes and addOverCapAttrs

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 `recordingSpan` `SetAttributes`. (#5864)
 
 ### Deprecated
 

sdk/trace/span.go

@@ -210,7 +210,7 @@ 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.IsRecording() || len(attributes) == 0 {
 		return
 	}
 
@@ -233,7 +233,7 @@ 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 +280,17 @@ 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)
-	s.dedupeAttrsFromRecord(&exists)
+	exists := make(map[attribute.Key]int, len(s.attributes))
+	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 +300,7 @@ 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
 		}
@@ -579,23 +584,23 @@ 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)
-	s.dedupeAttrsFromRecord(&exists)
+	exists := make(map[attribute.Key]int, len(s.attributes))
+	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