Cleanup interaction of exemplar and aggregation (#5899)

Follow-up to
https://github.com/open-telemetry/opentelemetry-go/pull/5861. This is an
attempt to:

* Limit the API surface of the aggregate package
* Try to use predefined types (e.g. exemplar.Filter) over custom
functions where possible.
* Avoid using nil, and use No-Ops where it makes sense

This makes `aggregate.NewFilteredExemplarReservoir` no longer exported,
removes the `aggregate.FilteredExemplarReservoir` interface, and removes
the `aggregate.dropReservoir`.

sdk/metric/exemplar.go

@@ -6,9 +6,7 @@ package metric // import "go.opentelemetry.io/otel/sdk/metric"
 import (
 	"runtime"
 
-	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/sdk/metric/exemplar"
-	"go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
 )
 
 // ExemplarReservoirProviderSelector selects the
@@ -16,14 +14,6 @@ import (
 // based on the [Aggregation] of the metric.
 type ExemplarReservoirProviderSelector func(Aggregation) exemplar.ReservoirProvider
 
-// reservoirFunc returns the appropriately configured exemplar reservoir
-// creation func based on the passed InstrumentKind and filter configuration.
-func reservoirFunc[N int64 | float64](provider exemplar.ReservoirProvider, filter exemplar.Filter) func(attribute.Set) aggregate.FilteredExemplarReservoir[N] {
-	return func(attrs attribute.Set) aggregate.FilteredExemplarReservoir[N] {
-		return aggregate.NewFilteredExemplarReservoir[N](filter, provider(attrs))
-	}
-}
-
 // DefaultExemplarReservoirProviderSelector returns the default
 // [exemplar.ReservoirProvider] for the
 // provided [Aggregation].

sdk/metric/instrument_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
@@ -22,7 +23,7 @@ func BenchmarkInstrument(b *testing.B) {
 	}
 
 	b.Run("instrumentImpl/aggregate", func(b *testing.B) {
-		build := aggregate.Builder[int64]{}
+		build := aggregate.Builder[int64]{ExemplarFilter: exemplar.AlwaysOffFilter, ExemplarReservoirProvider: exemplar.FixedSizeReservoirProvider(0)}
 		var meas []aggregate.Measure[int64]
 
 		build.Temporality = metricdata.CumulativeTemporality
@@ -52,7 +53,7 @@ func BenchmarkInstrument(b *testing.B) {
 	})
 
 	b.Run("observable/observe", func(b *testing.B) {
-		build := aggregate.Builder[int64]{}
+		build := aggregate.Builder[int64]{ExemplarFilter: exemplar.AlwaysOffFilter, ExemplarReservoirProvider: exemplar.FixedSizeReservoirProvider(0)}
 		var meas []aggregate.Measure[int64]
 
 		in, _ := build.PrecomputedLastValue()

sdk/metric/internal/aggregate/aggregate.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
@@ -33,12 +34,12 @@ type Builder[N int64 | float64] struct {
 	// Filter is the attribute filter the aggregate function will use on the
 	// input of measurements.
 	Filter attribute.Filter
-	// ReservoirFunc is the factory function used by aggregate functions to
-	// create new exemplar reservoirs for a new seen attribute set.
-	//
-	// If this is not provided a default factory function that returns an
-	// dropReservoir reservoir will be used.
-	ReservoirFunc func(attribute.Set) FilteredExemplarReservoir[N]
+	// ExemplarFilter is the filter applied to measurements before offering
+	// them to the exemplar Reservoir.
+	ExemplarFilter exemplar.Filter
+	// ExemplarReservoirProvider is the factory function used to create a new
+	// exemplar Reservoir for a given attribute set.
+	ExemplarReservoirProvider exemplar.ReservoirProvider
 	// AggregationLimit is the cardinality limit of measurement attributes. Any
 	// measurement for new attributes once the limit has been reached will be
 	// aggregated into a single aggregate for the "otel.metric.overflow"
@@ -49,12 +50,10 @@ type Builder[N int64 | float64] struct {
 	AggregationLimit int
 }
 
-func (b Builder[N]) resFunc() func(attribute.Set) FilteredExemplarReservoir[N] {
-	if b.ReservoirFunc != nil {
-		return b.ReservoirFunc
+func (b Builder[N]) resFunc() func(attribute.Set) *filteredExemplarReservoir[N] {
+	return func(attrs attribute.Set) *filteredExemplarReservoir[N] {
+		return newFilteredExemplarReservoir[N](b.ExemplarFilter, b.ExemplarReservoirProvider(attrs))
 	}
-
-	return dropReservoir
 }
 
 type fltrMeasure[N int64 | float64] func(ctx context.Context, value N, fltrAttr attribute.Set, droppedAttr []attribute.KeyValue)

sdk/metric/internal/aggregate/aggregate_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/stretchr/testify/assert"
 
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest"
 )
@@ -72,8 +73,12 @@ func (c *clock) Register() (unregister func()) {
 	return func() { now = orig }
 }
 
-func dropExemplars[N int64 | float64](attr attribute.Set) FilteredExemplarReservoir[N] {
-	return dropReservoir[N](attr)
+func newNoopReservoir(attribute.Set) exemplar.Reservoir {
+	return exemplar.NewFixedSizeReservoir(0)
+}
+
+func dropExemplars[N int64 | float64](attr attribute.Set) *filteredExemplarReservoir[N] {
+	return newFilteredExemplarReservoir[N](exemplar.AlwaysOffFilter, newNoopReservoir(attr))
 }
 
 func TestBuilderFilter(t *testing.T) {
@@ -99,8 +104,8 @@ func testBuilderFilter[N int64 | float64]() func(t *testing.T) {
 			}
 		}
 
-		t.Run("NoFilter", run(Builder[N]{}, attr, nil))
-		t.Run("Filter", run(Builder[N]{Filter: attrFltr}, fltrAlice, []attribute.KeyValue{adminTrue}))
+		t.Run("NoFilter", run(Builder[N]{ExemplarFilter: exemplar.AlwaysOffFilter, ExemplarReservoirProvider: newNoopReservoir}, attr, nil))
+		t.Run("Filter", run(Builder[N]{ExemplarFilter: exemplar.AlwaysOffFilter, ExemplarReservoirProvider: newNoopReservoir, Filter: attrFltr}, fltrAlice, []attribute.KeyValue{adminTrue}))
 	}
 }
 

sdk/metric/internal/aggregate/drop.go

@@ -1,26 +0,0 @@
-// Copyright The OpenTelemetry Authors
-// SPDX-License-Identifier: Apache-2.0
-
-package aggregate // import "go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
-
-import (
-	"context"
-
-	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/sdk/metric/exemplar"
-)
-
-// dropReservoir returns a [FilteredReservoir] that drops all measurements it is offered.
-func dropReservoir[N int64 | float64](attribute.Set) FilteredExemplarReservoir[N] {
-	return &dropRes[N]{}
-}
-
-type dropRes[N int64 | float64] struct{}
-
-// Offer does nothing, all measurements offered will be dropped.
-func (r *dropRes[N]) Offer(context.Context, N, []attribute.KeyValue) {}
-
-// Collect resets dest. No exemplars will ever be returned.
-func (r *dropRes[N]) Collect(dest *[]exemplar.Exemplar) {
-	*dest = (*dest)[:0]
-}

sdk/metric/internal/aggregate/drop_test.go

@@ -1,27 +0,0 @@
-// Copyright The OpenTelemetry Authors
-// SPDX-License-Identifier: Apache-2.0
-
-package aggregate
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-
-	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/sdk/metric/exemplar"
-)
-
-func TestDrop(t *testing.T) {
-	t.Run("Int64", testDropFiltered[int64])
-	t.Run("Float64", testDropFiltered[float64])
-}
-
-func testDropFiltered[N int64 | float64](t *testing.T) {
-	r := dropReservoir[N](*attribute.EmptySet())
-
-	var dest []exemplar.Exemplar
-	r.Collect(&dest)
-
-	assert.Empty(t, dest, "non-sampled context should not be offered")
-}

sdk/metric/internal/aggregate/exponential_histogram.go

@@ -30,7 +30,7 @@ const (
 // expoHistogramDataPoint is a single data point in an exponential histogram.
 type expoHistogramDataPoint[N int64 | float64] struct {
 	attrs attribute.Set
-	res   FilteredExemplarReservoir[N]
+	res   *filteredExemplarReservoir[N]
 
 	count uint64
 	min   N
@@ -283,7 +283,7 @@ func (b *expoBuckets) downscale(delta int32) {
 // newExponentialHistogram returns an Aggregator that summarizes a set of
 // measurements as an exponential histogram. Each histogram is scoped by attributes
 // and the aggregation cycle the measurements were made in.
-func newExponentialHistogram[N int64 | float64](maxSize, maxScale int32, noMinMax, noSum bool, limit int, r func(attribute.Set) FilteredExemplarReservoir[N]) *expoHistogram[N] {
+func newExponentialHistogram[N int64 | float64](maxSize, maxScale int32, noMinMax, noSum bool, limit int, r func(attribute.Set) *filteredExemplarReservoir[N]) *expoHistogram[N] {
 	return &expoHistogram[N]{
 		noSum:    noSum,
 		noMinMax: noMinMax,
@@ -306,7 +306,7 @@ type expoHistogram[N int64 | float64] struct {
 	maxSize  int
 	maxScale int32
 
-	newRes   func(attribute.Set) FilteredExemplarReservoir[N]
+	newRes   func(attribute.Set) *filteredExemplarReservoir[N]
 	limit    limiter[*expoHistogramDataPoint[N]]
 	values   map[attribute.Distinct]*expoHistogramDataPoint[N]
 	valuesMu sync.Mutex

sdk/metric/internal/aggregate/exponential_histogram_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"go.opentelemetry.io/otel/internal/global"
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
@@ -682,22 +683,30 @@ func BenchmarkExponentialHistogram(b *testing.B) {
 
 	b.Run("Int64/Cumulative", benchmarkAggregate(func() (Measure[int64], ComputeAggregation) {
 		return Builder[int64]{
-			Temporality: metricdata.CumulativeTemporality,
+			Temporality:               metricdata.CumulativeTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.ExponentialBucketHistogram(maxSize, maxScale, noMinMax, noSum)
 	}))
 	b.Run("Int64/Delta", benchmarkAggregate(func() (Measure[int64], ComputeAggregation) {
 		return Builder[int64]{
-			Temporality: metricdata.DeltaTemporality,
+			Temporality:               metricdata.DeltaTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.ExponentialBucketHistogram(maxSize, maxScale, noMinMax, noSum)
 	}))
 	b.Run("Float64/Cumulative", benchmarkAggregate(func() (Measure[float64], ComputeAggregation) {
 		return Builder[float64]{
-			Temporality: metricdata.CumulativeTemporality,
+			Temporality:               metricdata.CumulativeTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.ExponentialBucketHistogram(maxSize, maxScale, noMinMax, noSum)
 	}))
 	b.Run("Float64/Delta", benchmarkAggregate(func() (Measure[float64], ComputeAggregation) {
 		return Builder[float64]{
-			Temporality: metricdata.DeltaTemporality,
+			Temporality:               metricdata.DeltaTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.ExponentialBucketHistogram(maxSize, maxScale, noMinMax, noSum)
 	}))
 }
@@ -744,9 +753,11 @@ func TestExponentialHistogramAggregation(t *testing.T) {
 
 func testDeltaExpoHist[N int64 | float64]() func(t *testing.T) {
 	in, out := Builder[N]{
-		Temporality:      metricdata.DeltaTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 2,
+		Temporality:               metricdata.DeltaTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          2,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.ExponentialBucketHistogram(4, 20, false, false)
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -871,9 +882,11 @@ func testDeltaExpoHist[N int64 | float64]() func(t *testing.T) {
 
 func testCumulativeExpoHist[N int64 | float64]() func(t *testing.T) {
 	in, out := Builder[N]{
-		Temporality:      metricdata.CumulativeTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 2,
+		Temporality:               metricdata.CumulativeTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          2,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.ExponentialBucketHistogram(4, 20, false, false)
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{

sdk/metric/internal/aggregate/filtered_reservoir.go

@@ -11,29 +11,16 @@ import (
 	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 )
 
-// FilteredExemplarReservoir wraps a [exemplar.Reservoir] with a filter.
-type FilteredExemplarReservoir[N int64 | float64] interface {
-	// Offer accepts the parameters associated with a measurement. The
-	// parameters will be stored as an exemplar if the filter decides to
-	// sample the measurement.
-	//
-	// The passed ctx needs to contain any baggage or span that were active
-	// when the measurement was made. This information may be used by the
-	// Reservoir in making a sampling decision.
-	Offer(ctx context.Context, val N, attr []attribute.KeyValue)
-	// Collect returns all the held exemplars in the reservoir.
-	Collect(dest *[]exemplar.Exemplar)
-}
-
 // filteredExemplarReservoir handles the pre-sampled exemplar of measurements made.
 type filteredExemplarReservoir[N int64 | float64] struct {
 	filter    exemplar.Filter
 	reservoir exemplar.Reservoir
 }
 
-// NewFilteredExemplarReservoir creates a [FilteredExemplarReservoir] which only offers values
-// that are allowed by the filter.
-func NewFilteredExemplarReservoir[N int64 | float64](f exemplar.Filter, r exemplar.Reservoir) FilteredExemplarReservoir[N] {
+// newFilteredExemplarReservoir creates a [FilteredExemplarReservoir] which
+// only offers values that are allowed by the filter. If the provided filter is
+// nil, all measurements are dropped..
+func newFilteredExemplarReservoir[N int64 | float64](f exemplar.Filter, r exemplar.Reservoir) *filteredExemplarReservoir[N] {
 	return &filteredExemplarReservoir[N]{
 		filter:    f,
 		reservoir: r,

sdk/metric/internal/aggregate/histogram.go

@@ -16,7 +16,7 @@ import (
 
 type buckets[N int64 | float64] struct {
 	attrs attribute.Set
-	res   FilteredExemplarReservoir[N]
+	res   *filteredExemplarReservoir[N]
 
 	counts   []uint64
 	count    uint64
@@ -47,13 +47,13 @@ type histValues[N int64 | float64] struct {
 	noSum  bool
 	bounds []float64
 
-	newRes   func(attribute.Set) FilteredExemplarReservoir[N]
+	newRes   func(attribute.Set) *filteredExemplarReservoir[N]
 	limit    limiter[*buckets[N]]
 	values   map[attribute.Distinct]*buckets[N]
 	valuesMu sync.Mutex
 }
 
-func newHistValues[N int64 | float64](bounds []float64, noSum bool, limit int, r func(attribute.Set) FilteredExemplarReservoir[N]) *histValues[N] {
+func newHistValues[N int64 | float64](bounds []float64, noSum bool, limit int, r func(attribute.Set) *filteredExemplarReservoir[N]) *histValues[N] {
 	// The responsibility of keeping all buckets correctly associated with the
 	// passed boundaries is ultimately this type's responsibility. Make a copy
 	// here so we can always guarantee this. Or, in the case of failure, have
@@ -108,7 +108,7 @@ func (s *histValues[N]) measure(ctx context.Context, value N, fltrAttr attribute
 
 // newHistogram returns an Aggregator that summarizes a set of measurements as
 // an histogram.
-func newHistogram[N int64 | float64](boundaries []float64, noMinMax, noSum bool, limit int, r func(attribute.Set) FilteredExemplarReservoir[N]) *histogram[N] {
+func newHistogram[N int64 | float64](boundaries []float64, noMinMax, noSum bool, limit int, r func(attribute.Set) *filteredExemplarReservoir[N]) *histogram[N] {
 	return &histogram[N]{
 		histValues: newHistValues[N](boundaries, noSum, limit, r),
 		noMinMax:   noMinMax,

sdk/metric/internal/aggregate/histogram_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest"
 )
@@ -51,9 +52,11 @@ type conf[N int64 | float64] struct {
 
 func testDeltaHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 	in, out := Builder[N]{
-		Temporality:      metricdata.DeltaTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.DeltaTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.ExplicitBucketHistogram(bounds, noMinMax, c.noSum)
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -138,9 +141,11 @@ func testDeltaHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 
 func testCumulativeHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 	in, out := Builder[N]{
-		Temporality:      metricdata.CumulativeTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.CumulativeTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.ExplicitBucketHistogram(bounds, noMinMax, c.noSum)
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -375,22 +380,30 @@ func TestDeltaHistogramReset(t *testing.T) {
 func BenchmarkHistogram(b *testing.B) {
 	b.Run("Int64/Cumulative", benchmarkAggregate(func() (Measure[int64], ComputeAggregation) {
 		return Builder[int64]{
-			Temporality: metricdata.CumulativeTemporality,
+			Temporality:               metricdata.CumulativeTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.ExplicitBucketHistogram(bounds, noMinMax, false)
 	}))
 	b.Run("Int64/Delta", benchmarkAggregate(func() (Measure[int64], ComputeAggregation) {
 		return Builder[int64]{
-			Temporality: metricdata.DeltaTemporality,
+			Temporality:               metricdata.DeltaTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.ExplicitBucketHistogram(bounds, noMinMax, false)
 	}))
 	b.Run("Float64/Cumulative", benchmarkAggregate(func() (Measure[float64], ComputeAggregation) {
 		return Builder[float64]{
-			Temporality: metricdata.CumulativeTemporality,
+			Temporality:               metricdata.CumulativeTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.ExplicitBucketHistogram(bounds, noMinMax, false)
 	}))
 	b.Run("Float64/Delta", benchmarkAggregate(func() (Measure[float64], ComputeAggregation) {
 		return Builder[float64]{
-			Temporality: metricdata.DeltaTemporality,
+			Temporality:               metricdata.DeltaTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.ExplicitBucketHistogram(bounds, noMinMax, false)
 	}))
 }

sdk/metric/internal/aggregate/lastvalue.go

@@ -16,10 +16,10 @@ import (
 type datapoint[N int64 | float64] struct {
 	attrs attribute.Set
 	value N
-	res   FilteredExemplarReservoir[N]
+	res   *filteredExemplarReservoir[N]
 }
 
-func newLastValue[N int64 | float64](limit int, r func(attribute.Set) FilteredExemplarReservoir[N]) *lastValue[N] {
+func newLastValue[N int64 | float64](limit int, r func(attribute.Set) *filteredExemplarReservoir[N]) *lastValue[N] {
 	return &lastValue[N]{
 		newRes: r,
 		limit:  newLimiter[datapoint[N]](limit),
@@ -32,7 +32,7 @@ func newLastValue[N int64 | float64](limit int, r func(attribute.Set) FilteredEx
 type lastValue[N int64 | float64] struct {
 	sync.Mutex
 
-	newRes func(attribute.Set) FilteredExemplarReservoir[N]
+	newRes func(attribute.Set) *filteredExemplarReservoir[N]
 	limit  limiter[datapoint[N]]
 	values map[attribute.Distinct]datapoint[N]
 	start  time.Time
@@ -114,7 +114,7 @@ func (s *lastValue[N]) copyDpts(dest *[]metricdata.DataPoint[N], t time.Time) in
 
 // newPrecomputedLastValue returns an aggregator that summarizes a set of
 // observations as the last one made.
-func newPrecomputedLastValue[N int64 | float64](limit int, r func(attribute.Set) FilteredExemplarReservoir[N]) *precomputedLastValue[N] {
+func newPrecomputedLastValue[N int64 | float64](limit int, r func(attribute.Set) *filteredExemplarReservoir[N]) *precomputedLastValue[N] {
 	return &precomputedLastValue[N]{lastValue: newLastValue[N](limit, r)}
 }
 

sdk/metric/internal/aggregate/lastvalue_test.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"testing"
 
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
@@ -36,9 +37,11 @@ func TestLastValue(t *testing.T) {
 
 func testDeltaLastValue[N int64 | float64]() func(*testing.T) {
 	in, out := Builder[N]{
-		Temporality:      metricdata.DeltaTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.DeltaTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.LastValue()
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -140,9 +143,11 @@ func testDeltaLastValue[N int64 | float64]() func(*testing.T) {
 
 func testCumulativeLastValue[N int64 | float64]() func(*testing.T) {
 	in, out := Builder[N]{
-		Temporality:      metricdata.CumulativeTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.CumulativeTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.LastValue()
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -262,9 +267,11 @@ func testCumulativeLastValue[N int64 | float64]() func(*testing.T) {
 
 func testDeltaPrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 	in, out := Builder[N]{
-		Temporality:      metricdata.DeltaTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.DeltaTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.PrecomputedLastValue()
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -366,9 +373,11 @@ func testDeltaPrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 
 func testCumulativePrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 	in, out := Builder[N]{
-		Temporality:      metricdata.CumulativeTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.CumulativeTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.PrecomputedLastValue()
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -469,6 +478,12 @@ func testCumulativePrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 }
 
 func BenchmarkLastValue(b *testing.B) {
-	b.Run("Int64", benchmarkAggregate(Builder[int64]{}.PrecomputedLastValue))
-	b.Run("Float64", benchmarkAggregate(Builder[float64]{}.PrecomputedLastValue))
+	b.Run("Int64", benchmarkAggregate(Builder[int64]{
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
+	}.PrecomputedLastValue))
+	b.Run("Float64", benchmarkAggregate(Builder[float64]{
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
+	}.PrecomputedLastValue))
 }

sdk/metric/internal/aggregate/sum.go

@@ -14,19 +14,19 @@ import (
 
 type sumValue[N int64 | float64] struct {
 	n     N
-	res   FilteredExemplarReservoir[N]
+	res   *filteredExemplarReservoir[N]
 	attrs attribute.Set
 }
 
 // valueMap is the storage for sums.
 type valueMap[N int64 | float64] struct {
 	sync.Mutex
-	newRes func(attribute.Set) FilteredExemplarReservoir[N]
+	newRes func(attribute.Set) *filteredExemplarReservoir[N]
 	limit  limiter[sumValue[N]]
 	values map[attribute.Distinct]sumValue[N]
 }
 
-func newValueMap[N int64 | float64](limit int, r func(attribute.Set) FilteredExemplarReservoir[N]) *valueMap[N] {
+func newValueMap[N int64 | float64](limit int, r func(attribute.Set) *filteredExemplarReservoir[N]) *valueMap[N] {
 	return &valueMap[N]{
 		newRes: r,
 		limit:  newLimiter[sumValue[N]](limit),
@@ -54,7 +54,7 @@ func (s *valueMap[N]) measure(ctx context.Context, value N, fltrAttr attribute.S
 // newSum returns an aggregator that summarizes a set of measurements as their
 // arithmetic sum. Each sum is scoped by attributes and the aggregation cycle
 // the measurements were made in.
-func newSum[N int64 | float64](monotonic bool, limit int, r func(attribute.Set) FilteredExemplarReservoir[N]) *sum[N] {
+func newSum[N int64 | float64](monotonic bool, limit int, r func(attribute.Set) *filteredExemplarReservoir[N]) *sum[N] {
 	return &sum[N]{
 		valueMap:  newValueMap[N](limit, r),
 		monotonic: monotonic,
@@ -143,7 +143,7 @@ func (s *sum[N]) cumulative(dest *metricdata.Aggregation) int {
 // newPrecomputedSum returns an aggregator that summarizes a set of
 // observations as their arithmetic sum. Each sum is scoped by attributes and
 // the aggregation cycle the measurements were made in.
-func newPrecomputedSum[N int64 | float64](monotonic bool, limit int, r func(attribute.Set) FilteredExemplarReservoir[N]) *precomputedSum[N] {
+func newPrecomputedSum[N int64 | float64](monotonic bool, limit int, r func(attribute.Set) *filteredExemplarReservoir[N]) *precomputedSum[N] {
 	return &precomputedSum[N]{
 		valueMap:  newValueMap[N](limit, r),
 		monotonic: monotonic,

sdk/metric/internal/aggregate/sum_test.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"testing"
 
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
@@ -41,9 +42,11 @@ func TestSum(t *testing.T) {
 func testDeltaSum[N int64 | float64]() func(t *testing.T) {
 	mono := false
 	in, out := Builder[N]{
-		Temporality:      metricdata.DeltaTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.DeltaTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.Sum(mono)
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -169,9 +172,11 @@ func testDeltaSum[N int64 | float64]() func(t *testing.T) {
 func testCumulativeSum[N int64 | float64]() func(t *testing.T) {
 	mono := false
 	in, out := Builder[N]{
-		Temporality:      metricdata.CumulativeTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.CumulativeTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.Sum(mono)
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -283,9 +288,11 @@ func testCumulativeSum[N int64 | float64]() func(t *testing.T) {
 func testDeltaPrecomputedSum[N int64 | float64]() func(t *testing.T) {
 	mono := false
 	in, out := Builder[N]{
-		Temporality:      metricdata.DeltaTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.DeltaTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.PrecomputedSum(mono)
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -412,9 +419,11 @@ func testDeltaPrecomputedSum[N int64 | float64]() func(t *testing.T) {
 func testCumulativePrecomputedSum[N int64 | float64]() func(t *testing.T) {
 	mono := false
 	in, out := Builder[N]{
-		Temporality:      metricdata.CumulativeTemporality,
-		Filter:           attrFltr,
-		AggregationLimit: 3,
+		Temporality:               metricdata.CumulativeTemporality,
+		Filter:                    attrFltr,
+		AggregationLimit:          3,
+		ExemplarFilter:            exemplar.AlwaysOffFilter,
+		ExemplarReservoirProvider: newNoopReservoir,
 	}.PrecomputedSum(mono)
 	ctx := context.Background()
 	return test[N](in, out, []teststep[N]{
@@ -544,43 +553,59 @@ func BenchmarkSum(b *testing.B) {
 	// performance, therefore, only monotonic=false is benchmarked here.
 	b.Run("Int64/Cumulative", benchmarkAggregate(func() (Measure[int64], ComputeAggregation) {
 		return Builder[int64]{
-			Temporality: metricdata.CumulativeTemporality,
+			Temporality:               metricdata.CumulativeTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.Sum(false)
 	}))
 	b.Run("Int64/Delta", benchmarkAggregate(func() (Measure[int64], ComputeAggregation) {
 		return Builder[int64]{
-			Temporality: metricdata.DeltaTemporality,
+			Temporality:               metricdata.DeltaTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.Sum(false)
 	}))
 	b.Run("Float64/Cumulative", benchmarkAggregate(func() (Measure[float64], ComputeAggregation) {
 		return Builder[float64]{
-			Temporality: metricdata.CumulativeTemporality,
+			Temporality:               metricdata.CumulativeTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.Sum(false)
 	}))
 	b.Run("Float64/Delta", benchmarkAggregate(func() (Measure[float64], ComputeAggregation) {
 		return Builder[float64]{
-			Temporality: metricdata.DeltaTemporality,
+			Temporality:               metricdata.DeltaTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.Sum(false)
 	}))
 
 	b.Run("Precomputed/Int64/Cumulative", benchmarkAggregate(func() (Measure[int64], ComputeAggregation) {
 		return Builder[int64]{
-			Temporality: metricdata.CumulativeTemporality,
+			Temporality:               metricdata.CumulativeTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.PrecomputedSum(false)
 	}))
 	b.Run("Precomputed/Int64/Delta", benchmarkAggregate(func() (Measure[int64], ComputeAggregation) {
 		return Builder[int64]{
-			Temporality: metricdata.DeltaTemporality,
+			Temporality:               metricdata.DeltaTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.PrecomputedSum(false)
 	}))
 	b.Run("Precomputed/Float64/Cumulative", benchmarkAggregate(func() (Measure[float64], ComputeAggregation) {
 		return Builder[float64]{
-			Temporality: metricdata.CumulativeTemporality,
+			Temporality:               metricdata.CumulativeTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.PrecomputedSum(false)
 	}))
 	b.Run("Precomputed/Float64/Delta", benchmarkAggregate(func() (Measure[float64], ComputeAggregation) {
 		return Builder[float64]{
-			Temporality: metricdata.DeltaTemporality,
+			Temporality:               metricdata.DeltaTemporality,
+			ExemplarFilter:            exemplar.AlwaysOffFilter,
+			ExemplarReservoirProvider: newNoopReservoir,
 		}.PrecomputedSum(false)
 	}))
 }

sdk/metric/pipeline.go

@@ -354,8 +354,9 @@ func (i *inserter[N]) cachedAggregator(scope instrumentation.Scope, kind Instrum
 	normID := id.normalize()
 	cv := i.aggregators.Lookup(normID, func() aggVal[N] {
 		b := aggregate.Builder[N]{
-			Temporality:   i.pipeline.reader.temporality(kind),
-			ReservoirFunc: reservoirFunc[N](stream.ExemplarReservoirProviderSelector(stream.Aggregation), i.pipeline.exemplarFilter),
+			Temporality:               i.pipeline.reader.temporality(kind),
+			ExemplarReservoirProvider: stream.ExemplarReservoirProviderSelector(stream.Aggregation),
+			ExemplarFilter:            i.pipeline.exemplarFilter,
 		}
 		b.Filter = stream.AttributeFilter
 		// A value less than or equal to zero will disable the aggregation