Pool sortables used to create attribute sets (open-telemetry#3832)

* Pool sortables used to create attribute sets

* Move sync pool to attribute pkg

* Add change to changelog

* Fix comment

* Apply suggestions from code review

Co-authored-by: Peter Liu <[email protected]>

* Update sdk/metric/instrument.go

Co-authored-by: Robert Pająk <[email protected]>

* Update comment based on feedback

* Apply feedback

---------

Co-authored-by: Peter Liu <[email protected]>
Co-authored-by: Robert Pająk <[email protected]>

CHANGELOG.md

@@ -14,6 +14,8 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ### Changed
 
+- Optimize memory allocation when creation a new `Set` using `NewSet` or `NewSetWithFiltered` in `go.opentelemetry.io/otel/attribute`. (#3832)
+- Optimize memory allocation when creation new metric instruments in `go.opentelemetry.io/otel/sdk/metric`. (#3832)
 - Avoid creating new objects on all calls to `WithDeferredSetup` and `SkipContextSetup` in OpenTracing bridge. (#3833)
 - The `New` and `Detect` functions from `go.opentelemetry.io/otel/sdk/resource` return errors that wrap underlying errors instead of just containing the underlying error strings. (#3844)
 

attribute/set.go

@@ -18,6 +18,7 @@ import (
 	"encoding/json"
 	"reflect"
 	"sort"
+	"sync"
 )
 
 type (
@@ -62,6 +63,12 @@ var (
 			iface: [0]KeyValue{},
 		},
 	}
+
+	// sortables is a pool of Sortables used to create Sets with a user does
+	// not provide one.
+	sortables = sync.Pool{
+		New: func() interface{} { return new(Sortable) },
+	}
 )
 
 // EmptySet returns a reference to a Set with no elements.
@@ -191,7 +198,9 @@ func NewSet(kvs ...KeyValue) Set {
 	if len(kvs) == 0 {
 		return empty()
 	}
-	s, _ := NewSetWithSortableFiltered(kvs, new(Sortable), nil)
+	srt := sortables.Get().(*Sortable)
+	s, _ := NewSetWithSortableFiltered(kvs, srt, nil)
+	sortables.Put(srt)
 	return s
 }
 
@@ -218,7 +227,10 @@ func NewSetWithFiltered(kvs []KeyValue, filter Filter) (Set, []KeyValue) {
 	if len(kvs) == 0 {
 		return empty(), nil
 	}
-	return NewSetWithSortableFiltered(kvs, new(Sortable), filter)
+	srt := sortables.Get().(*Sortable)
+	s, filtered := NewSetWithSortableFiltered(kvs, srt, filter)
+	sortables.Put(srt)
+	return s, filtered
 }
 
 // NewSetWithSortableFiltered returns a new Set.

sdk/metric/instrument.go

@@ -194,8 +194,12 @@ func (i *instrumentImpl[N]) aggregate(ctx context.Context, val N, attrs []attrib
 	if err := ctx.Err(); err != nil {
 		return
 	}
+	// Do not use single attribute.Sortable and attribute.NewSetWithSortable,
+	// this method needs to be concurrent safe. Let the sync.Pool in the
+	// attribute package handle allocations of the Sortable.
+	s := attribute.NewSet(attrs...)
 	for _, agg := range i.aggregators {
-		agg.Aggregate(val, attribute.NewSet(attrs...))
+		agg.Aggregate(val, s)
 	}
 }
 
@@ -260,8 +264,12 @@ func newObservable[N int64 | float64](scope instrumentation.Scope, kind Instrume
 
 // observe records the val for the set of attrs.
 func (o *observable[N]) observe(val N, attrs []attribute.KeyValue) {
+	// Do not use single attribute.Sortable and attribute.NewSetWithSortable,
+	// this method needs to be concurrent safe. Let the sync.Pool in the
+	// attribute package handle allocations of the Sortable.
+	s := attribute.NewSet(attrs...)
 	for _, agg := range o.aggregators {
-		agg.Aggregate(val, attribute.NewSet(attrs...))
+		agg.Aggregate(val, s)
 	}
 }
 

sdk/metric/instrument_test.go

@@ -0,0 +1,62 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metric
+
+import (
+	"context"
+	"testing"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/metric/internal"
+)
+
+func BenchmarkInstrument(b *testing.B) {
+	attr := func(id int) []attribute.KeyValue {
+		return []attribute.KeyValue{
+			attribute.String("user", "Alice"),
+			attribute.Bool("admin", true),
+			attribute.Int("id", id),
+		}
+	}
+
+	b.Run("instrumentImpl/aggregate", func(b *testing.B) {
+		inst := instrumentImpl[int64]{aggregators: []internal.Aggregator[int64]{
+			internal.NewLastValue[int64](),
+			internal.NewCumulativeSum[int64](true),
+			internal.NewDeltaSum[int64](true),
+		}}
+		ctx := context.Background()
+
+		b.ReportAllocs()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			inst.aggregate(ctx, int64(i), attr(i))
+		}
+	})
+
+	b.Run("observable/observe", func(b *testing.B) {
+		o := observable[int64]{aggregators: []internal.Aggregator[int64]{
+			internal.NewLastValue[int64](),
+			internal.NewCumulativeSum[int64](true),
+			internal.NewDeltaSum[int64](true),
+		}}
+
+		b.ReportAllocs()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			o.observe(int64(i), attr(i))
+		}
+	})
+}