[chore][pkg/resourcetotelemetry] reduce memory usage by call ensure c…

…apacity (#29430)

Description:

1. Reduce memory usage by ensure capacity before merge two maps

Link to tracking Issue:

N/A

Testing:

N/A

Documentation:

N/A

pkg/resourcetotelemetry/resource_to_telemetry.go

@@ -107,6 +107,7 @@ func addAttributesToExponentialHistogramDataPoints(ps pmetric.ExponentialHistogr
 }
 
 func joinAttributeMaps(from, to pcommon.Map) {
+	to.EnsureCapacity(from.Len() + to.Len())
 	from.Range(func(k string, v pcommon.Value) bool {
 		v.CopyTo(to.PutEmpty(k))
 		return true

pkg/resourcetotelemetry/resource_to_telemetry_test.go

@@ -3,9 +3,11 @@
 package resourcetotelemetry
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"go.opentelemetry.io/collector/pdata/pcommon"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/coreinternal/testdata"
 )
@@ -65,3 +67,71 @@ func TestConvertResourceToAttributesAllDataTypesEmptyDataPoint(t *testing.T) {
 	assert.Equal(t, 0, md.ResourceMetrics().At(0).ScopeMetrics().At(0).Metrics().At(6).ExponentialHistogram().DataPoints().At(0).Attributes().Len())
 
 }
+
+func BenchmarkJoinAttributes(b *testing.B) {
+	type args struct {
+		from int
+		to   int
+	}
+	tests := []struct {
+		name string
+		args args
+	}{
+		{
+			name: "merge 10 into 10",
+			args: args{
+				from: 10,
+				to:   10,
+			},
+		},
+		{
+			name: "merge 10 into 20",
+			args: args{
+				from: 10,
+				to:   20,
+			},
+		},
+		{
+			name: "merge 20 into 10",
+			args: args{
+				from: 20,
+				to:   10,
+			},
+		},
+		{
+			name: "merge 30 into 10",
+			args: args{
+				from: 30,
+				to:   10,
+			},
+		},
+		{
+			name: "merge 10 into 30",
+			args: args{
+				from: 10,
+				to:   30,
+			},
+		},
+	}
+	b.ReportAllocs()
+	for _, tt := range tests {
+		b.Run(tt.name, func(b *testing.B) {
+			b.ResetTimer()
+			from := initMetricAttributes(tt.args.from, 0)
+			for i := 0; i < b.N; i++ {
+				to := initMetricAttributes(tt.args.to, tt.args.from)
+				joinAttributeMaps(from, to)
+			}
+		})
+	}
+
+}
+
+func initMetricAttributes(capacity int, idx int) pcommon.Map {
+	dest := pcommon.NewMap()
+	dest.EnsureCapacity(capacity)
+	for i := 0; i < capacity; i++ {
+		dest.PutStr(fmt.Sprintf("label-name-for-index-%d", i+idx), fmt.Sprintf("label-value-for-index-%d", i+idx))
+	}
+	return dest
+}