Move time.Now call into exemplar reservoir to improve performance (#5545)

Part of addressing https://github.com/open-telemetry/opentelemetry-go/issues/5542. ### Motivation This removes the `time.Now()` call from filtered-out Exemplars by only invoking `time.Now()` after the filtering decision is made. This improvement is especially noticeable for measurements without any attributes. ``` goos: linux goarch: amd64 pkg: go.opentelemetry.io/otel/sdk/metric cpu: AMD EPYC 7B12 │ old.txt │ new.txt │ │ sec/op │ sec/op vs base │ SyncMeasure/NoView/Int64Counter/Attributes/0-24 158.20n ± 4% 99.83n ± 1% -36.90% (p=0.000 n=10) SyncMeasure/NoView/Int64Counter/Attributes/1-24 333.3n ± 4% 274.8n ± 1% -17.55% (p=0.000 n=10) SyncMeasure/NoView/Int64Counter/Attributes/10-24 1.640µ ± 1% 1.600µ ± 1% -2.41% (p=0.000 n=10) SyncMeasure/NoView/Float64Counter/Attributes/0-24 159.0n ± 3% 101.3n ± 0% -36.27% (p=0.000 n=10) SyncMeasure/NoView/Float64Counter/Attributes/1-24 340.0n ± 2% 272.0n ± 1% -20.00% (p=0.000 n=10) SyncMeasure/NoView/Float64Counter/Attributes/10-24 1.661µ ± 1% 1.597µ ± 0% -3.85% (p=0.000 n=10) SyncMeasure/NoView/Int64UpDownCounter/Attributes/0-24 159.8n ± 1% 103.1n ± 0% -35.50% (p=0.000 n=10) SyncMeasure/NoView/Int64UpDownCounter/Attributes/1-24 339.5n ± 1% 273.1n ± 0% -19.57% (p=0.000 n=10) SyncMeasure/NoView/Int64UpDownCounter/Attributes/10-24 1.656µ ± 0% 1.589µ ± 0% -4.05% (p=0.000 n=10) SyncMeasure/NoView/Float64UpDownCounter/Attributes/0-24 159.3n ± 2% 100.8n ± 0% -36.74% (p=0.000 n=10) SyncMeasure/NoView/Float64UpDownCounter/Attributes/1-24 337.9n ± 2% 271.8n ± 1% -19.55% (p=0.000 n=10) SyncMeasure/NoView/Float64UpDownCounter/Attributes/10-24 1.657µ ± 0% 1.593µ ± 1% -3.83% (p=0.000 n=10) SyncMeasure/NoView/Int64Histogram/Attributes/0-24 144.65n ± 4% 89.38n ± 0% -38.21% (p=0.000 n=10) SyncMeasure/NoView/Int64Histogram/Attributes/1-24 235.7n ± 2% 183.5n ± 0% -22.15% (p=0.000 n=10) SyncMeasure/NoView/Int64Histogram/Attributes/10-24 900.8n ± 1% 836.8n ± 0% -7.10% (p=0.000 n=10) SyncMeasure/NoView/Float64Histogram/Attributes/0-24 145.60n ± 5% 93.48n ± 1% -35.80% (p=0.000 n=10) SyncMeasure/NoView/Float64Histogram/Attributes/1-24 240.9n ± 1% 183.0n ± 0% -24.06% (p=0.000 n=10) SyncMeasure/NoView/Float64Histogram/Attributes/10-24 905.6n ± 1% 826.3n ± 0% -8.76% (p=0.000 n=10) SyncMeasure/DropView/Int64Counter/Attributes/0-24 20.33n ± 0% 20.35n ± 0% ~ (p=0.302 n=10) SyncMeasure/DropView/Int64Counter/Attributes/1-24 26.46n ± 0% 26.45n ± 1% ~ (p=0.868 n=10) SyncMeasure/DropView/Int64Counter/Attributes/10-24 26.50n ± 0% 26.47n ± 0% ~ (p=0.208 n=10) SyncMeasure/DropView/Float64Counter/Attributes/0-24 20.34n ± 1% 20.27n ± 0% -0.34% (p=0.009 n=10) SyncMeasure/DropView/Float64Counter/Attributes/1-24 26.55n ± 0% 26.60n ± 1% ~ (p=0.109 n=10) SyncMeasure/DropView/Float64Counter/Attributes/10-24 26.59n ± 1% 26.57n ± 1% ~ (p=0.926 n=10) SyncMeasure/DropView/Int64UpDownCounter/Attributes/0-24 20.38n ± 1% 20.38n ± 0% ~ (p=0.725 n=10) SyncMeasure/DropView/Int64UpDownCounter/Attributes/1-24 26.39n ± 0% 26.44n ± 0% ~ (p=0.238 n=10) SyncMeasure/DropView/Int64UpDownCounter/Attributes/10-24 26.52n ± 0% 26.42n ± 0% -0.36% (p=0.049 n=10) SyncMeasure/DropView/Float64UpDownCounter/Attributes/0-24 20.30n ± 0% 20.25n ± 0% ~ (p=0.196 n=10) SyncMeasure/DropView/Float64UpDownCounter/Attributes/1-24 26.57n ± 0% 26.54n ± 1% ~ (p=0.540 n=10) SyncMeasure/DropView/Float64UpDownCounter/Attributes/10-24 26.57n ± 0% 26.51n ± 1% ~ (p=0.643 n=10) SyncMeasure/DropView/Int64Histogram/Attributes/0-24 20.37n ± 0% 20.36n ± 1% ~ (p=1.000 n=10) SyncMeasure/DropView/Int64Histogram/Attributes/1-24 26.41n ± 0% 26.50n ± 0% +0.32% (p=0.007 n=10) SyncMeasure/DropView/Int64Histogram/Attributes/10-24 26.44n ± 0% 26.55n ± 1% +0.42% (p=0.012 n=10) SyncMeasure/DropView/Float64Histogram/Attributes/0-24 20.30n ± 0% 20.45n ± 0% +0.74% (p=0.000 n=10) SyncMeasure/DropView/Float64Histogram/Attributes/1-24 26.52n ± 0% 26.48n ± 0% ~ (p=0.127 n=10) SyncMeasure/DropView/Float64Histogram/Attributes/10-24 26.55n ± 0% 26.48n ± 0% -0.26% (p=0.002 n=10) SyncMeasure/AttrFilterView/Int64Counter/Attributes/0-24 170.5n ± 2% 110.8n ± 0% -35.03% (p=0.000 n=10) SyncMeasure/AttrFilterView/Int64Counter/Attributes/1-24 402.5n ± 1% 331.5n ± 1% -17.64% (p=0.000 n=10) SyncMeasure/AttrFilterView/Int64Counter/Attributes/10-24 1.363µ ± 1% 1.281µ ± 1% -6.02% (p=0.000 n=10) SyncMeasure/AttrFilterView/Float64Counter/Attributes/0-24 170.6n ± 1% 111.5n ± 1% -34.64% (p=0.000 n=10) SyncMeasure/AttrFilterView/Float64Counter/Attributes/1-24 397.1n ± 1% 335.9n ± 0% -15.41% (p=0.000 n=10) SyncMeasure/AttrFilterView/Float64Counter/Attributes/10-24 1.371µ ± 1% 1.279µ ± 1% -6.71% (p=0.000 n=10) SyncMeasure/AttrFilterView/Int64UpDownCounter/Attributes/0-24 170.1n ± 1% 112.2n ± 0% -34.09% (p=0.000 n=10) SyncMeasure/AttrFilterView/Int64UpDownCounter/Attributes/1-24 397.5n ± 1% 330.2n ± 0% -16.93% (p=0.000 n=10) SyncMeasure/AttrFilterView/Int64UpDownCounter/Attributes/10-24 1.371µ ± 1% 1.289µ ± 1% -5.95% (p=0.000 n=10) SyncMeasure/AttrFilterView/Float64UpDownCounter/Attributes/0-24 171.4n ± 2% 112.9n ± 0% -34.13% (p=0.000 n=10) SyncMeasure/AttrFilterView/Float64UpDownCounter/Attributes/1-24 397.0n ± 3% 336.4n ± 0% -15.24% (p=0.000 n=10) SyncMeasure/AttrFilterView/Float64UpDownCounter/Attributes/10-24 1.383µ ± 1% 1.305µ ± 1% -5.61% (p=0.000 n=10) SyncMeasure/AttrFilterView/Int64Histogram/Attributes/0-24 157.30n ± 2% 98.58n ± 1% -37.33% (p=0.000 n=6+10) ``` ### Changes * Introduce `exemplar.Filter`, which is a filter function based on the context. It will not be user-facing, so we can always add other parameters later if needed. * Introduce `exemplar.FilteredReservoir`, which is similar to a reservoir, except it does not receive a timestamp. It gets the current time after the filter decision has been made. It uses generics to avoid the call to exemplar.NewValue(), since it is internal-only. * The `exemplar.Reservoir` is left as-is, so that it can be made public when exemplars are stable. It still includes a timestamp argument. * Unit tests are updated to expect a much lower number of calls to time.Now * `exemplar.Drop` is now an `exemplar.FilteredReservoir` instead of a `Reservoir`, since we don't need a Reservoir to store things in if the measurement is always dropped. Co-authored-by: Sam Xie <sam@samxie.me> Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
2025-08-10 22:31:50 +02:00 · 2024-07-01 12:36:11 -04:00
parent 1cefb17de7
commit 0485de287e
18 changed files with 264 additions and 232 deletions
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -30,6 +30,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Upgrade `go.opentelemetry.io/otel/semconv/v1.25.0` to `go.opentelemetry.io/otel/semconv/v1.26.0` in `go.opentelemetry.io/otel/sdk/resource`. (#5490)
 - Upgrade `go.opentelemetry.io/otel/semconv/v1.25.0` to `go.opentelemetry.io/otel/semconv/v1.26.0` in `go.opentelemetry.io/otel/sdk/trace`. (#5490)
 - Use non-generic functions in the `Start` method of `"go.opentelemetry.io/otel/sdk/trace".Trace` to reduce memory allocation. (#5497)
+- Improve performance of metric instruments in `go.opentelemetry.io/otel/sdk/metric` by removing unnecessary calls to time.Now. (#5545)

 ### Fixed

--- a/sdk/metric/exemplar.go
+++ b/sdk/metric/exemplar.go
@@ -19,67 +19,63 @@ import (
 // Note: This will only return non-nil values when the experimental exemplar
 // feature is enabled and the OTEL_METRICS_EXEMPLAR_FILTER environment variable
 // is not set to always_off.
-func reservoirFunc(agg Aggregation) func() exemplar.Reservoir {
+func reservoirFunc[N int64 | float64](agg Aggregation) func() exemplar.FilteredReservoir[N] {
 	if !x.Exemplars.Enabled() {
 		return nil
 	}
-
-	// https://github.com/open-telemetry/opentelemetry-specification/blob/d4b241f451674e8f611bb589477680341006ad2b/specification/metrics/sdk.md#exemplar-defaults
-	resF := func() func() exemplar.Reservoir {
-		// Explicit bucket histogram aggregation with more than 1 bucket will
-		// use AlignedHistogramBucketExemplarReservoir.
-		a, ok := agg.(AggregationExplicitBucketHistogram)
-		if ok && len(a.Boundaries) > 0 {
-			cp := slices.Clone(a.Boundaries)
-			return func() exemplar.Reservoir {
-				bounds := cp
-				return exemplar.Histogram(bounds)
-			}
-		}
-
-		var n int
-		if a, ok := agg.(AggregationBase2ExponentialHistogram); ok {
-			// Base2 Exponential Histogram Aggregation SHOULD use a
-			// SimpleFixedSizeExemplarReservoir with a reservoir equal to the
-			// smaller of the maximum number of buckets configured on the
-			// aggregation or twenty (e.g. min(20, max_buckets)).
-			n = int(a.MaxSize)
-			if n > 20 {
-				n = 20
-			}
-		} else {
-			// https://github.com/open-telemetry/opentelemetry-specification/blob/e94af89e3d0c01de30127a0f423e912f6cda7bed/specification/metrics/sdk.md#simplefixedsizeexemplarreservoir
-			//   This Exemplar reservoir MAY take a configuration parameter for
-			//   the size of the reservoir. If no size configuration is
-			//   provided, the default size MAY be the number of possible
-			//   concurrent threads (e.g. number of CPUs) to help reduce
-			//   contention. Otherwise, a default size of 1 SHOULD be used.
-			n = runtime.NumCPU()
-			if n < 1 {
-				// Should never be the case, but be defensive.
-				n = 1
-			}
-		}
-
-		return func() exemplar.Reservoir {
-			return exemplar.FixedSize(n)
-		}
-	}
-
 	// https://github.com/open-telemetry/opentelemetry-specification/blob/d4b241f451674e8f611bb589477680341006ad2b/specification/configuration/sdk-environment-variables.md#exemplar
 	const filterEnvKey = "OTEL_METRICS_EXEMPLAR_FILTER"

+	var filter exemplar.Filter
+
 	switch os.Getenv(filterEnvKey) {
 	case "always_on":
-		return resF()
+		filter = exemplar.AlwaysOnFilter
 	case "always_off":
 		return exemplar.Drop
 	case "trace_based":
 		fallthrough
 	default:
-		newR := resF()
-		return func() exemplar.Reservoir {
-			return exemplar.SampledFilter(newR())
+		filter = exemplar.SampledFilter
+	}
+
+	// https://github.com/open-telemetry/opentelemetry-specification/blob/d4b241f451674e8f611bb589477680341006ad2b/specification/metrics/sdk.md#exemplar-defaults
+	// Explicit bucket histogram aggregation with more than 1 bucket will
+	// use AlignedHistogramBucketExemplarReservoir.
+	a, ok := agg.(AggregationExplicitBucketHistogram)
+	if ok && len(a.Boundaries) > 0 {
+		cp := slices.Clone(a.Boundaries)
+		return func() exemplar.FilteredReservoir[N] {
+			bounds := cp
+			return exemplar.NewFilteredReservoir[N](filter, exemplar.Histogram(bounds))
 		}
 	}
+
+	var n int
+	if a, ok := agg.(AggregationBase2ExponentialHistogram); ok {
+		// Base2 Exponential Histogram Aggregation SHOULD use a
+		// SimpleFixedSizeExemplarReservoir with a reservoir equal to the
+		// smaller of the maximum number of buckets configured on the
+		// aggregation or twenty (e.g. min(20, max_buckets)).
+		n = int(a.MaxSize)
+		if n > 20 {
+			n = 20
+		}
+	} else {
+		// https://github.com/open-telemetry/opentelemetry-specification/blob/e94af89e3d0c01de30127a0f423e912f6cda7bed/specification/metrics/sdk.md#simplefixedsizeexemplarreservoir
+		//   This Exemplar reservoir MAY take a configuration parameter for
+		//   the size of the reservoir. If no size configuration is
+		//   provided, the default size MAY be the number of possible
+		//   concurrent threads (e.g. number of CPUs) to help reduce
+		//   contention. Otherwise, a default size of 1 SHOULD be used.
+		n = runtime.NumCPU()
+		if n < 1 {
+			// Should never be the case, but be defensive.
+			n = 1
+		}
+	}
+
+	return func() exemplar.FilteredReservoir[N] {
+		return exemplar.NewFilteredReservoir[N](filter, exemplar.FixedSize(n))
+	}
 }
--- a/sdk/metric/internal/aggregate/aggregate.go
+++ b/sdk/metric/internal/aggregate/aggregate.go
@@ -39,7 +39,7 @@ type Builder[N int64 | float64] struct {
 	//
 	// If this is not provided a default factory function that returns an
 	// exemplar.Drop reservoir will be used.
-	ReservoirFunc func() exemplar.Reservoir
+	ReservoirFunc func() exemplar.FilteredReservoir[N]
 	// 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"
@@ -50,7 +50,7 @@ type Builder[N int64 | float64] struct {
 	AggregationLimit int
 }

-func (b Builder[N]) resFunc() func() exemplar.Reservoir {
+func (b Builder[N]) resFunc() func() exemplar.FilteredReservoir[N] {
 	if b.ReservoirFunc != nil {
 		return b.ReservoirFunc
 	}
--- a/sdk/metric/internal/aggregate/aggregate_test.go
+++ b/sdk/metric/internal/aggregate/aggregate_test.go
@@ -73,8 +73,8 @@ func (c *clock) Register() (unregister func()) {
 	return func() { now = orig }
 }

-func dropExemplars[N int64 | float64]() exemplar.Reservoir {
-	return exemplar.Drop()
+func dropExemplars[N int64 | float64]() exemplar.FilteredReservoir[N] {
+	return exemplar.Drop[N]()
 }

 func TestBuilderFilter(t *testing.T) {
--- a/sdk/metric/internal/aggregate/exponential_histogram.go
+++ b/sdk/metric/internal/aggregate/exponential_histogram.go
@@ -31,7 +31,7 @@ const (
 // expoHistogramDataPoint is a single data point in an exponential histogram.
 type expoHistogramDataPoint[N int64 | float64] struct {
 	attrs attribute.Set
-	res   exemplar.Reservoir
+	res   exemplar.FilteredReservoir[N]

 	count uint64
 	min   N
@@ -282,7 +282,7 @@ func (b *expoBuckets) downscale(delta int) {
 // 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() exemplar.Reservoir) *expoHistogram[N] {
+func newExponentialHistogram[N int64 | float64](maxSize, maxScale int32, noMinMax, noSum bool, limit int, r func() exemplar.FilteredReservoir[N]) *expoHistogram[N] {
 	return &expoHistogram[N]{
 		noSum:    noSum,
 		noMinMax: noMinMax,
@@ -305,7 +305,7 @@ type expoHistogram[N int64 | float64] struct {
 	maxSize  int
 	maxScale int

-	newRes   func() exemplar.Reservoir
+	newRes   func() exemplar.FilteredReservoir[N]
 	limit    limiter[*expoHistogramDataPoint[N]]
 	values   map[attribute.Distinct]*expoHistogramDataPoint[N]
 	valuesMu sync.Mutex
@@ -319,8 +319,6 @@ func (e *expoHistogram[N]) measure(ctx context.Context, value N, fltrAttr attrib
 		return
 	}

-	t := now()
-
 	e.valuesMu.Lock()
 	defer e.valuesMu.Unlock()

@@ -333,7 +331,7 @@ func (e *expoHistogram[N]) measure(ctx context.Context, value N, fltrAttr attrib
 		e.values[attr.Equivalent()] = v
 	}
 	v.record(value)
-	v.res.Offer(ctx, t, exemplar.NewValue(value), droppedAttr)
+	v.res.Offer(ctx, value, droppedAttr)
 }

 func (e *expoHistogram[N]) delta(dest *metricdata.Aggregation) int {
--- a/sdk/metric/internal/aggregate/exponential_histogram_test.go
+++ b/sdk/metric/internal/aggregate/exponential_histogram_test.go
@@ -778,7 +778,7 @@ func testDeltaExpoHist[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(1),
-							Time:       y2kPlus(9),
+							Time:       y2kPlus(2),
 							Count:      7,
 							Min:        metricdata.NewExtrema[N](-1),
 							Max:        metricdata.NewExtrema[N](16),
@@ -832,8 +832,8 @@ func testDeltaExpoHist[N int64 | float64]() func(t *testing.T) {
 					DataPoints: []metricdata.ExponentialHistogramDataPoint[N]{
 						{
 							Attributes: fltrAlice,
-							StartTime:  y2kPlus(10),
-							Time:       y2kPlus(24),
+							StartTime:  y2kPlus(3),
+							Time:       y2kPlus(4),
 							Count:      7,
 							Min:        metricdata.NewExtrema[N](-1),
 							Max:        metricdata.NewExtrema[N](16),
@@ -850,8 +850,8 @@ func testDeltaExpoHist[N int64 | float64]() func(t *testing.T) {
 						},
 						{
 							Attributes: overflowSet,
-							StartTime:  y2kPlus(10),
-							Time:       y2kPlus(24),
+							StartTime:  y2kPlus(3),
+							Time:       y2kPlus(4),
 							Count:      6,
 							Min:        metricdata.NewExtrema[N](1),
 							Max:        metricdata.NewExtrema[N](16),
@@ -905,7 +905,7 @@ func testCumulativeExpoHist[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(9),
+							Time:       y2kPlus(2),
 							Count:      7,
 							Min:        metricdata.NewExtrema[N](-1),
 							Max:        metricdata.NewExtrema[N](16),
@@ -938,7 +938,7 @@ func testCumulativeExpoHist[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(13),
+							Time:       y2kPlus(3),
 							Count:      10,
 							Min:        metricdata.NewExtrema[N](-1),
 							Max:        metricdata.NewExtrema[N](16),
@@ -967,7 +967,7 @@ func testCumulativeExpoHist[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(14),
+							Time:       y2kPlus(4),
 							Count:      10,
 							Min:        metricdata.NewExtrema[N](-1),
 							Max:        metricdata.NewExtrema[N](16),
@@ -1004,7 +1004,7 @@ func testCumulativeExpoHist[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(21),
+							Time:       y2kPlus(5),
 							Count:      10,
 							Min:        metricdata.NewExtrema[N](-1),
 							Max:        metricdata.NewExtrema[N](16),
@@ -1022,7 +1022,7 @@ func testCumulativeExpoHist[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: overflowSet,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(21),
+							Time:       y2kPlus(5),
 							Count:      6,
 							Min:        metricdata.NewExtrema[N](1),
 							Max:        metricdata.NewExtrema[N](16),
--- a/sdk/metric/internal/aggregate/histogram.go
+++ b/sdk/metric/internal/aggregate/histogram.go
@@ -17,7 +17,7 @@ import (

 type buckets[N int64 | float64] struct {
 	attrs attribute.Set
-	res   exemplar.Reservoir
+	res   exemplar.FilteredReservoir[N]

 	counts   []uint64
 	count    uint64
@@ -48,13 +48,13 @@ type histValues[N int64 | float64] struct {
 	noSum  bool
 	bounds []float64

-	newRes   func() exemplar.Reservoir
+	newRes   func() exemplar.FilteredReservoir[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() exemplar.Reservoir) *histValues[N] {
+func newHistValues[N int64 | float64](bounds []float64, noSum bool, limit int, r func() exemplar.FilteredReservoir[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
@@ -80,8 +80,6 @@ func (s *histValues[N]) measure(ctx context.Context, value N, fltrAttr attribute
 	// (s.bounds[len(s.bounds)-1], +∞).
 	idx := sort.SearchFloat64s(s.bounds, float64(value))

-	t := now()
-
 	s.valuesMu.Lock()
 	defer s.valuesMu.Unlock()

@@ -106,12 +104,12 @@ func (s *histValues[N]) measure(ctx context.Context, value N, fltrAttr attribute
 	if !s.noSum {
 		b.sum(value)
 	}
-	b.res.Offer(ctx, t, exemplar.NewValue(value), droppedAttr)
+	b.res.Offer(ctx, value, droppedAttr)
 }

 // 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() exemplar.Reservoir) *histogram[N] {
+func newHistogram[N int64 | float64](boundaries []float64, noMinMax, noSum bool, limit int, r func() exemplar.FilteredReservoir[N]) *histogram[N] {
 	return &histogram[N]{
 		histValues: newHistValues[N](boundaries, noSum, limit, r),
 		noMinMax:   noMinMax,
--- a/sdk/metric/internal/aggregate/histogram_test.go
+++ b/sdk/metric/internal/aggregate/histogram_test.go
@@ -80,8 +80,8 @@ func testDeltaHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 				agg: metricdata.Histogram[N]{
 					Temporality: metricdata.DeltaTemporality,
 					DataPoints: []metricdata.HistogramDataPoint[N]{
-						c.hPt(fltrAlice, 2, 3, y2kPlus(1), y2kPlus(7)),
-						c.hPt(fltrBob, 10, 2, y2kPlus(1), y2kPlus(7)),
+						c.hPt(fltrAlice, 2, 3, y2kPlus(1), y2kPlus(2)),
+						c.hPt(fltrBob, 10, 2, y2kPlus(1), y2kPlus(2)),
 					},
 				},
 			},
@@ -96,8 +96,8 @@ func testDeltaHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 				agg: metricdata.Histogram[N]{
 					Temporality: metricdata.DeltaTemporality,
 					DataPoints: []metricdata.HistogramDataPoint[N]{
-						c.hPt(fltrAlice, 10, 1, y2kPlus(7), y2kPlus(10)),
-						c.hPt(fltrBob, 3, 1, y2kPlus(7), y2kPlus(10)),
+						c.hPt(fltrAlice, 10, 1, y2kPlus(2), y2kPlus(3)),
+						c.hPt(fltrBob, 3, 1, y2kPlus(2), y2kPlus(3)),
 					},
 				},
 			},
@@ -126,9 +126,9 @@ func testDeltaHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 				agg: metricdata.Histogram[N]{
 					Temporality: metricdata.DeltaTemporality,
 					DataPoints: []metricdata.HistogramDataPoint[N]{
-						c.hPt(fltrAlice, 1, 1, y2kPlus(11), y2kPlus(16)),
-						c.hPt(fltrBob, 1, 1, y2kPlus(11), y2kPlus(16)),
-						c.hPt(overflowSet, 1, 2, y2kPlus(11), y2kPlus(16)),
+						c.hPt(fltrAlice, 1, 1, y2kPlus(4), y2kPlus(5)),
+						c.hPt(fltrBob, 1, 1, y2kPlus(4), y2kPlus(5)),
+						c.hPt(overflowSet, 1, 2, y2kPlus(4), y2kPlus(5)),
 					},
 				},
 			},
@@ -167,8 +167,8 @@ func testCumulativeHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 				agg: metricdata.Histogram[N]{
 					Temporality: metricdata.CumulativeTemporality,
 					DataPoints: []metricdata.HistogramDataPoint[N]{
-						c.hPt(fltrAlice, 2, 3, y2kPlus(0), y2kPlus(7)),
-						c.hPt(fltrBob, 10, 2, y2kPlus(0), y2kPlus(7)),
+						c.hPt(fltrAlice, 2, 3, y2kPlus(0), y2kPlus(2)),
+						c.hPt(fltrBob, 10, 2, y2kPlus(0), y2kPlus(2)),
 					},
 				},
 			},
@@ -183,8 +183,8 @@ func testCumulativeHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 				agg: metricdata.Histogram[N]{
 					Temporality: metricdata.CumulativeTemporality,
 					DataPoints: []metricdata.HistogramDataPoint[N]{
-						c.hPt(fltrAlice, 2, 4, y2kPlus(0), y2kPlus(10)),
-						c.hPt(fltrBob, 10, 3, y2kPlus(0), y2kPlus(10)),
+						c.hPt(fltrAlice, 2, 4, y2kPlus(0), y2kPlus(3)),
+						c.hPt(fltrBob, 10, 3, y2kPlus(0), y2kPlus(3)),
 					},
 				},
 			},
@@ -196,8 +196,8 @@ func testCumulativeHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 				agg: metricdata.Histogram[N]{
 					Temporality: metricdata.CumulativeTemporality,
 					DataPoints: []metricdata.HistogramDataPoint[N]{
-						c.hPt(fltrAlice, 2, 4, y2kPlus(0), y2kPlus(11)),
-						c.hPt(fltrBob, 10, 3, y2kPlus(0), y2kPlus(11)),
+						c.hPt(fltrAlice, 2, 4, y2kPlus(0), y2kPlus(4)),
+						c.hPt(fltrBob, 10, 3, y2kPlus(0), y2kPlus(4)),
 					},
 				},
 			},
@@ -213,9 +213,9 @@ func testCumulativeHist[N int64 | float64](c conf[N]) func(t *testing.T) {
 				agg: metricdata.Histogram[N]{
 					Temporality: metricdata.CumulativeTemporality,
 					DataPoints: []metricdata.HistogramDataPoint[N]{
-						c.hPt(fltrAlice, 2, 4, y2kPlus(0), y2kPlus(14)),
-						c.hPt(fltrBob, 10, 3, y2kPlus(0), y2kPlus(14)),
-						c.hPt(overflowSet, 1, 2, y2kPlus(0), y2kPlus(14)),
+						c.hPt(fltrAlice, 2, 4, y2kPlus(0), y2kPlus(5)),
+						c.hPt(fltrBob, 10, 3, y2kPlus(0), y2kPlus(5)),
+						c.hPt(overflowSet, 1, 2, y2kPlus(0), y2kPlus(5)),
 					},
 				},
 			},
--- a/sdk/metric/internal/aggregate/lastvalue.go
+++ b/sdk/metric/internal/aggregate/lastvalue.go
@@ -17,10 +17,10 @@ import (
 type datapoint[N int64 | float64] struct {
 	attrs attribute.Set
 	value N
-	res   exemplar.Reservoir
+	res   exemplar.FilteredReservoir[N]
 }

-func newLastValue[N int64 | float64](limit int, r func() exemplar.Reservoir) *lastValue[N] {
+func newLastValue[N int64 | float64](limit int, r func() exemplar.FilteredReservoir[N]) *lastValue[N] {
 	return &lastValue[N]{
 		newRes: r,
 		limit:  newLimiter[datapoint[N]](limit),
@@ -33,15 +33,13 @@ func newLastValue[N int64 | float64](limit int, r func() exemplar.Reservoir) *la
 type lastValue[N int64 | float64] struct {
 	sync.Mutex

-	newRes func() exemplar.Reservoir
+	newRes func() exemplar.FilteredReservoir[N]
 	limit  limiter[datapoint[N]]
 	values map[attribute.Distinct]datapoint[N]
 	start  time.Time
 }

 func (s *lastValue[N]) measure(ctx context.Context, value N, fltrAttr attribute.Set, droppedAttr []attribute.KeyValue) {
-	t := now()
-
 	s.Lock()
 	defer s.Unlock()

@@ -53,7 +51,7 @@ func (s *lastValue[N]) measure(ctx context.Context, value N, fltrAttr attribute.

 	d.attrs = attr
 	d.value = value
-	d.res.Offer(ctx, t, exemplar.NewValue(value), droppedAttr)
+	d.res.Offer(ctx, value, droppedAttr)

 	s.values[attr.Equivalent()] = d
 }
@@ -117,7 +115,7 @@ 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() exemplar.Reservoir) *precomputedLastValue[N] {
+func newPrecomputedLastValue[N int64 | float64](limit int, r func() exemplar.FilteredReservoir[N]) *precomputedLastValue[N] {
 	return &precomputedLastValue[N]{lastValue: newLastValue[N](limit, r)}
 }

--- a/sdk/metric/internal/aggregate/lastvalue_test.go
+++ b/sdk/metric/internal/aggregate/lastvalue_test.go
@@ -61,13 +61,13 @@ func testDeltaLastValue[N int64 | float64]() func(*testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(1),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      2,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(1),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      -10,
 						},
 					},
@@ -88,14 +88,14 @@ func testDeltaLastValue[N int64 | float64]() func(*testing.T) {
 					DataPoints: []metricdata.DataPoint[N]{
 						{
 							Attributes: fltrAlice,
-							StartTime:  y2kPlus(8),
-							Time:       y2kPlus(11),
+							StartTime:  y2kPlus(3),
+							Time:       y2kPlus(4),
 							Value:      10,
 						},
 						{
 							Attributes: fltrBob,
-							StartTime:  y2kPlus(8),
-							Time:       y2kPlus(11),
+							StartTime:  y2kPlus(3),
+							Time:       y2kPlus(4),
 							Value:      3,
 						},
 					},
@@ -115,20 +115,20 @@ func testDeltaLastValue[N int64 | float64]() func(*testing.T) {
 					DataPoints: []metricdata.DataPoint[N]{
 						{
 							Attributes: fltrAlice,
-							StartTime:  y2kPlus(11),
-							Time:       y2kPlus(16),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: fltrBob,
-							StartTime:  y2kPlus(11),
-							Time:       y2kPlus(16),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: overflowSet,
-							StartTime:  y2kPlus(11),
-							Time:       y2kPlus(16),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 					},
@@ -165,13 +165,13 @@ func testCumulativeLastValue[N int64 | float64]() func(*testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      2,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      -10,
 						},
 					},
@@ -187,13 +187,13 @@ func testCumulativeLastValue[N int64 | float64]() func(*testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(8),
+							Time:       y2kPlus(3),
 							Value:      2,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(8),
+							Time:       y2kPlus(3),
 							Value:      -10,
 						},
 					},
@@ -211,13 +211,13 @@ func testCumulativeLastValue[N int64 | float64]() func(*testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(11),
+							Time:       y2kPlus(4),
 							Value:      10,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(11),
+							Time:       y2kPlus(4),
 							Value:      3,
 						},
 					},
@@ -238,19 +238,19 @@ func testCumulativeLastValue[N int64 | float64]() func(*testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(16),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(16),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: overflowSet,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(16),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 					},
@@ -287,13 +287,13 @@ func testDeltaPrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(1),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      2,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(1),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      -10,
 						},
 					},
@@ -314,14 +314,14 @@ func testDeltaPrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 					DataPoints: []metricdata.DataPoint[N]{
 						{
 							Attributes: fltrAlice,
-							StartTime:  y2kPlus(8),
-							Time:       y2kPlus(11),
+							StartTime:  y2kPlus(3),
+							Time:       y2kPlus(4),
 							Value:      10,
 						},
 						{
 							Attributes: fltrBob,
-							StartTime:  y2kPlus(8),
-							Time:       y2kPlus(11),
+							StartTime:  y2kPlus(3),
+							Time:       y2kPlus(4),
 							Value:      3,
 						},
 					},
@@ -341,20 +341,20 @@ func testDeltaPrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 					DataPoints: []metricdata.DataPoint[N]{
 						{
 							Attributes: fltrAlice,
-							StartTime:  y2kPlus(11),
-							Time:       y2kPlus(16),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: fltrBob,
-							StartTime:  y2kPlus(11),
-							Time:       y2kPlus(16),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: overflowSet,
-							StartTime:  y2kPlus(11),
-							Time:       y2kPlus(16),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 					},
@@ -391,13 +391,13 @@ func testCumulativePrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      2,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      -10,
 						},
 					},
@@ -419,13 +419,13 @@ func testCumulativePrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(11),
+							Time:       y2kPlus(4),
 							Value:      10,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(11),
+							Time:       y2kPlus(4),
 							Value:      3,
 						},
 					},
@@ -446,19 +446,19 @@ func testCumulativePrecomputedLastValue[N int64 | float64]() func(*testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(16),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(16),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: overflowSet,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(16),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 					},
--- a/sdk/metric/internal/aggregate/sum.go
+++ b/sdk/metric/internal/aggregate/sum.go
@@ -15,19 +15,19 @@ import (

 type sumValue[N int64 | float64] struct {
 	n     N
-	res   exemplar.Reservoir
+	res   exemplar.FilteredReservoir[N]
 	attrs attribute.Set
 }

 // valueMap is the storage for sums.
 type valueMap[N int64 | float64] struct {
 	sync.Mutex
-	newRes func() exemplar.Reservoir
+	newRes func() exemplar.FilteredReservoir[N]
 	limit  limiter[sumValue[N]]
 	values map[attribute.Distinct]sumValue[N]
 }

-func newValueMap[N int64 | float64](limit int, r func() exemplar.Reservoir) *valueMap[N] {
+func newValueMap[N int64 | float64](limit int, r func() exemplar.FilteredReservoir[N]) *valueMap[N] {
 	return &valueMap[N]{
 		newRes: r,
 		limit:  newLimiter[sumValue[N]](limit),
@@ -36,8 +36,6 @@ func newValueMap[N int64 | float64](limit int, r func() exemplar.Reservoir) *val
 }

 func (s *valueMap[N]) measure(ctx context.Context, value N, fltrAttr attribute.Set, droppedAttr []attribute.KeyValue) {
-	t := now()
-
 	s.Lock()
 	defer s.Unlock()

@@ -49,7 +47,7 @@ func (s *valueMap[N]) measure(ctx context.Context, value N, fltrAttr attribute.S

 	v.attrs = attr
 	v.n += value
-	v.res.Offer(ctx, t, exemplar.NewValue(value), droppedAttr)
+	v.res.Offer(ctx, value, droppedAttr)

 	s.values[attr.Equivalent()] = v
 }
@@ -57,7 +55,7 @@ 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() exemplar.Reservoir) *sum[N] {
+func newSum[N int64 | float64](monotonic bool, limit int, r func() exemplar.FilteredReservoir[N]) *sum[N] {
 	return &sum[N]{
 		valueMap:  newValueMap[N](limit, r),
 		monotonic: monotonic,
@@ -146,7 +144,7 @@ func (s *sum[N]) cumulative(dest *metricdata.Aggregation) int {
 // newPrecomputedSum returns an aggregator that summarizes a set of
 // observatrions 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() exemplar.Reservoir) *precomputedSum[N] {
+func newPrecomputedSum[N int64 | float64](monotonic bool, limit int, r func() exemplar.FilteredReservoir[N]) *precomputedSum[N] {
 	return &precomputedSum[N]{
 		valueMap:  newValueMap[N](limit, r),
 		monotonic: monotonic,
--- a/sdk/metric/internal/aggregate/sum_test.go
+++ b/sdk/metric/internal/aggregate/sum_test.go
@@ -75,13 +75,13 @@ func testDeltaSum[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(1),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      4,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(1),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      -11,
 						},
 					},
@@ -101,14 +101,14 @@ func testDeltaSum[N int64 | float64]() func(t *testing.T) {
 					DataPoints: []metricdata.DataPoint[N]{
 						{
 							Attributes: fltrAlice,
-							StartTime:  y2kPlus(7),
-							Time:       y2kPlus(10),
+							StartTime:  y2kPlus(2),
+							Time:       y2kPlus(3),
 							Value:      10,
 						},
 						{
 							Attributes: fltrBob,
-							StartTime:  y2kPlus(7),
-							Time:       y2kPlus(10),
+							StartTime:  y2kPlus(2),
+							Time:       y2kPlus(3),
 							Value:      3,
 						},
 					},
@@ -143,20 +143,20 @@ func testDeltaSum[N int64 | float64]() func(t *testing.T) {
 					DataPoints: []metricdata.DataPoint[N]{
 						{
 							Attributes: fltrAlice,
-							StartTime:  y2kPlus(11),
-							Time:       y2kPlus(16),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: fltrBob,
-							StartTime:  y2kPlus(11),
-							Time:       y2kPlus(16),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: overflowSet,
-							StartTime:  y2kPlus(11),
-							Time:       y2kPlus(16),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      2,
 						},
 					},
@@ -203,13 +203,13 @@ func testCumulativeSum[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      4,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      -11,
 						},
 					},
@@ -230,13 +230,13 @@ func testCumulativeSum[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(10),
+							Time:       y2kPlus(3),
 							Value:      14,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(10),
+							Time:       y2kPlus(3),
 							Value:      -8,
 						},
 					},
@@ -258,19 +258,19 @@ func testCumulativeSum[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(13),
+							Time:       y2kPlus(4),
 							Value:      14,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(13),
+							Time:       y2kPlus(4),
 							Value:      -8,
 						},
 						{
 							Attributes: overflowSet,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(13),
+							Time:       y2kPlus(4),
 							Value:      2,
 						},
 					},
@@ -317,13 +317,13 @@ func testDeltaPrecomputedSum[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(1),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      4,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(1),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      -11,
 						},
 					},
@@ -344,14 +344,14 @@ func testDeltaPrecomputedSum[N int64 | float64]() func(t *testing.T) {
 					DataPoints: []metricdata.DataPoint[N]{
 						{
 							Attributes: fltrAlice,
-							StartTime:  y2kPlus(7),
-							Time:       y2kPlus(11),
+							StartTime:  y2kPlus(2),
+							Time:       y2kPlus(3),
 							Value:      7,
 						},
 						{
 							Attributes: fltrBob,
-							StartTime:  y2kPlus(7),
-							Time:       y2kPlus(11),
+							StartTime:  y2kPlus(2),
+							Time:       y2kPlus(3),
 							Value:      14,
 						},
 					},
@@ -386,20 +386,20 @@ func testDeltaPrecomputedSum[N int64 | float64]() func(t *testing.T) {
 					DataPoints: []metricdata.DataPoint[N]{
 						{
 							Attributes: fltrAlice,
-							StartTime:  y2kPlus(12),
-							Time:       y2kPlus(17),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: fltrBob,
-							StartTime:  y2kPlus(12),
-							Time:       y2kPlus(17),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: overflowSet,
-							StartTime:  y2kPlus(12),
-							Time:       y2kPlus(17),
+							StartTime:  y2kPlus(4),
+							Time:       y2kPlus(5),
 							Value:      2,
 						},
 					},
@@ -446,13 +446,13 @@ func testCumulativePrecomputedSum[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      4,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(7),
+							Time:       y2kPlus(2),
 							Value:      -11,
 						},
 					},
@@ -474,13 +474,13 @@ func testCumulativePrecomputedSum[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(11),
+							Time:       y2kPlus(3),
 							Value:      11,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(11),
+							Time:       y2kPlus(3),
 							Value:      3,
 						},
 					},
@@ -516,19 +516,19 @@ func testCumulativePrecomputedSum[N int64 | float64]() func(t *testing.T) {
 						{
 							Attributes: fltrAlice,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(17),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: fltrBob,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(17),
+							Time:       y2kPlus(5),
 							Value:      1,
 						},
 						{
 							Attributes: overflowSet,
 							StartTime:  y2kPlus(0),
-							Time:       y2kPlus(17),
+							Time:       y2kPlus(5),
 							Value:      2,
 						},
 					},
--- a/sdk/metric/internal/exemplar/drop.go
+++ b/sdk/metric/internal/exemplar/drop.go
@@ -5,20 +5,19 @@ package exemplar // import "go.opentelemetry.io/otel/sdk/metric/internal/exempla

 import (
 	"context"
-	"time"

 	"go.opentelemetry.io/otel/attribute"
 )

-// Drop returns a [Reservoir] that drops all measurements it is offered.
-func Drop() Reservoir { return &dropRes{} }
+// Drop returns a [FilteredReservoir] that drops all measurements it is offered.
+func Drop[N int64 | float64]() FilteredReservoir[N] { return &dropRes[N]{} }

-type dropRes struct{}
+type dropRes[N int64 | float64] struct{}

 // Offer does nothing, all measurements offered will be dropped.
-func (r *dropRes) Offer(context.Context, time.Time, Value, []attribute.KeyValue) {}
+func (r *dropRes[N]) Offer(context.Context, N, []attribute.KeyValue) {}

 // Collect resets dest. No exemplars will ever be returned.
-func (r *dropRes) Collect(dest *[]Exemplar) {
+func (r *dropRes[N]) Collect(dest *[]Exemplar) {
 	*dest = (*dest)[:0]
 }
--- a/sdk/metric/internal/exemplar/drop_test.go
+++ b/sdk/metric/internal/exemplar/drop_test.go
@@ -5,14 +5,20 @@ package exemplar

 import (
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )

 func TestDrop(t *testing.T) {
-	t.Run("Int64", ReservoirTest[int64](func(int) (Reservoir, int) {
-		return Drop(), 0
-	}))
-
-	t.Run("Float64", ReservoirTest[float64](func(int) (Reservoir, int) {
-		return Drop(), 0
-	}))
+	t.Run("Int64", testDropFiltered[int64])
+	t.Run("Float64", testDropFiltered[float64])
+}
+
+func testDropFiltered[N int64 | float64](t *testing.T) {
+	r := Drop[N]()
+
+	var dest []Exemplar
+	r.Collect(&dest)
+
+	assert.Len(t, dest, 0, "non-sampled context should not be offered")
 }
--- a/sdk/metric/internal/exemplar/filter.go
+++ b/sdk/metric/internal/exemplar/filter.go
@@ -5,25 +5,25 @@ package exemplar // import "go.opentelemetry.io/otel/sdk/metric/internal/exempla

 import (
 	"context"
-	"time"

-	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/trace"
 )

-// SampledFilter returns a [Reservoir] wrapping r that will only offer measurements
-// to r if the passed context associated with the measurement contains a sampled
+// Filter determines if a measurement should be offered.
+//
+// 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.
+type Filter func(context.Context) bool
+
+// SampledFilter is a [Filter] that will only offer measurements
+// if the passed context associated with the measurement contains a sampled
 // [go.opentelemetry.io/otel/trace.SpanContext].
-func SampledFilter(r Reservoir) Reservoir {
-	return filtered{Reservoir: r}
+func SampledFilter(ctx context.Context) bool {
+	return trace.SpanContextFromContext(ctx).IsSampled()
 }

-type filtered struct {
-	Reservoir
-}
-
-func (f filtered) Offer(ctx context.Context, t time.Time, n Value, a []attribute.KeyValue) {
-	if trace.SpanContextFromContext(ctx).IsSampled() {
-		f.Reservoir.Offer(ctx, t, n, a)
-	}
+// AlwaysOnFilter is a [Filter] that always offers measurements.
+func AlwaysOnFilter(ctx context.Context) bool {
+	return true
 }
--- a/sdk/metric/internal/exemplar/filter_test.go
+++ b/sdk/metric/internal/exemplar/filter_test.go
@@ -6,11 +6,9 @@ package exemplar // import "go.opentelemetry.io/otel/sdk/metric/internal/exempla
 import (
 	"context"
 	"testing"
-	"time"

 	"github.com/stretchr/testify/assert"

-	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/trace"
 )

@@ -20,18 +18,10 @@ func TestSampledFilter(t *testing.T) {
 }

 func testSampledFiltered[N int64 | float64](t *testing.T) {
-	under := &res{}
-
-	r := SampledFilter(under)
-
 	ctx := context.Background()
-	r.Offer(ctx, staticTime, NewValue(N(0)), nil)
-	assert.False(t, under.OfferCalled, "underlying Reservoir Offer called")
-	r.Offer(sample(ctx), staticTime, NewValue(N(0)), nil)
-	assert.True(t, under.OfferCalled, "underlying Reservoir Offer not called")

-	r.Collect(nil)
-	assert.True(t, under.CollectCalled, "underlying Reservoir Collect not called")
+	assert.False(t, SampledFilter(ctx), "non-sampled context should not be offered")
+	assert.True(t, SampledFilter(sample(ctx)), "sampled context should be offered")
 }

 func sample(parent context.Context) context.Context {
@@ -43,15 +33,14 @@ func sample(parent context.Context) context.Context {
 	return trace.ContextWithSpanContext(parent, sc)
 }

-type res struct {
-	OfferCalled   bool
-	CollectCalled bool
+func TestAlwaysOnFilter(t *testing.T) {
+	t.Run("Int64", testAlwaysOnFiltered[int64])
+	t.Run("Float64", testAlwaysOnFiltered[float64])
 }

-func (r *res) Offer(context.Context, time.Time, Value, []attribute.KeyValue) {
-	r.OfferCalled = true
-}
+func testAlwaysOnFiltered[N int64 | float64](t *testing.T) {
+	ctx := context.Background()

-func (r *res) Collect(*[]Exemplar) {
-	r.CollectCalled = true
+	assert.True(t, AlwaysOnFilter(ctx), "non-sampled context should not be offered")
+	assert.True(t, AlwaysOnFilter(sample(ctx)), "sampled context should be offered")
 }
--- a/sdk/metric/internal/exemplar/filtered_reservoir.go
+++ b/sdk/metric/internal/exemplar/filtered_reservoir.go
@@ -0,0 +1,49 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package exemplar // import "go.opentelemetry.io/otel/sdk/metric/internal/exemplar"
+
+import (
+	"context"
+	"time"
+
+	"go.opentelemetry.io/otel/attribute"
+)
+
+// FilteredReservoir wraps a [Reservoir] with a filter.
+type FilteredReservoir[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)
+}
+
+// filteredReservoir handles the pre-sampled exemplar of measurements made.
+type filteredReservoir[N int64 | float64] struct {
+	filter    Filter
+	reservoir Reservoir
+}
+
+// NewFilteredReservoir creates a [FilteredReservoir] which only offers values
+// that are allowed by the filter.
+func NewFilteredReservoir[N int64 | float64](f Filter, r Reservoir) FilteredReservoir[N] {
+	return &filteredReservoir[N]{
+		filter:    f,
+		reservoir: r,
+	}
+}
+
+func (f *filteredReservoir[N]) Offer(ctx context.Context, val N, attr []attribute.KeyValue) {
+	if f.filter(ctx) {
+		// only record the current time if we are sampling this measurment.
+		f.reservoir.Offer(ctx, time.Now(), NewValue(val), attr)
+	}
+}
+
+func (f *filteredReservoir[N]) Collect(dest *[]Exemplar) { f.reservoir.Collect(dest) }
--- a/sdk/metric/pipeline.go
+++ b/sdk/metric/pipeline.go
@@ -349,7 +349,7 @@ func (i *inserter[N]) cachedAggregator(scope instrumentation.Scope, kind Instrum
 	cv := i.aggregators.Lookup(normID, func() aggVal[N] {
 		b := aggregate.Builder[N]{
 			Temporality:   i.pipeline.reader.temporality(kind),
-			ReservoirFunc: reservoirFunc(stream.Aggregation),
+			ReservoirFunc: reservoirFunc[N](stream.Aggregation),
 		}
 		b.Filter = stream.AttributeFilter
 		// A value less than or equal to zero will disable the aggregation