diff --git a/metrics/histogram.go b/metrics/histogram.go
index db294a9d3e..5f7e299624 100644
--- a/metrics/histogram.go
+++ b/metrics/histogram.go
@@ -7,7 +7,7 @@ type HistogramSnapshot interface {
 	Min() int64
 	Percentile(float64) float64
 	Percentiles([]float64) []float64
-	Sample() Sample
+	Sample() SampleSnapshot
 	StdDev() float64
 	Sum() int64
 	Variance() float64
@@ -59,7 +59,7 @@ func NewRegisteredHistogram(name string, r Registry, s Sample) Histogram {
 
 // histogramSnapshot is a read-only copy of another Histogram.
 type histogramSnapshot struct {
-	sample *SampleSnapshot
+	sample *sampleSnapshot
 }
 
 // Count returns the number of samples recorded at the time the snapshot was
@@ -91,7 +91,7 @@ func (h *histogramSnapshot) Percentiles(ps []float64) []float64 {
 }
 
 // Sample returns the Sample underlying the histogram.
-func (h *histogramSnapshot) Sample() Sample { return h.sample }
+func (h *histogramSnapshot) Sample() SampleSnapshot { return h.sample }
 
 // Snapshot returns the snapshot.
 func (h *histogramSnapshot) Snapshot() HistogramSnapshot { return h }
@@ -133,7 +133,7 @@ func (NilHistogram) Percentiles(ps []float64) []float64 {
 }
 
 // Sample is a no-op.
-func (NilHistogram) Sample() Sample { return NilSample{} }
+func (NilHistogram) Sample() SampleSnapshot { return NilSample{} }
 
 // Snapshot is a no-op.
 func (NilHistogram) Snapshot() HistogramSnapshot { return NilHistogram{} }
@@ -161,7 +161,7 @@ func (h *StandardHistogram) Clear() { h.sample.Clear() }
 
 // Snapshot returns a read-only copy of the histogram.
 func (h *StandardHistogram) Snapshot() HistogramSnapshot {
-	return &histogramSnapshot{sample: h.sample.Snapshot().(*SampleSnapshot)}
+	return &histogramSnapshot{sample: h.sample.Snapshot().(*sampleSnapshot)}
 }
 
 // Update samples a new value.
diff --git a/metrics/resetting_sample.go b/metrics/resetting_sample.go
index 43c1129cd0..c38ffcd3ec 100644
--- a/metrics/resetting_sample.go
+++ b/metrics/resetting_sample.go
@@ -17,7 +17,7 @@ type resettingSample struct {
 }
 
 // Snapshot returns a read-only copy of the sample with the original reset.
-func (rs *resettingSample) Snapshot() Sample {
+func (rs *resettingSample) Snapshot() SampleSnapshot {
 	s := rs.Sample.Snapshot()
 	rs.Sample.Clear()
 	return s
diff --git a/metrics/runtimehistogram.go b/metrics/runtimehistogram.go
index f93a7188d9..6abdb67d59 100644
--- a/metrics/runtimehistogram.go
+++ b/metrics/runtimehistogram.go
@@ -57,69 +57,15 @@ func (h *runtimeHistogram) Clear() {
 func (h *runtimeHistogram) Update(int64) {
 	panic("runtimeHistogram does not support Update")
 }
-func (h *runtimeHistogram) Sample() Sample {
-	return NilSample{}
-}
 
 // Snapshot returns a non-changing cop of the histogram.
 func (h *runtimeHistogram) Snapshot() HistogramSnapshot {
 	return h.load()
 }
 
-// Count returns the sample count.
-func (h *runtimeHistogram) Count() int64 {
-	return h.load().Count()
-}
-
-// Mean returns an approximation of the mean.
-func (h *runtimeHistogram) Mean() float64 {
-	return h.load().Mean()
-}
-
-// StdDev approximates the standard deviation of the histogram.
-func (h *runtimeHistogram) StdDev() float64 {
-	return h.load().StdDev()
-}
-
-// Variance approximates the variance of the histogram.
-func (h *runtimeHistogram) Variance() float64 {
-	return h.load().Variance()
-}
-
-// Percentile computes the p'th percentile value.
-func (h *runtimeHistogram) Percentile(p float64) float64 {
-	return h.load().Percentile(p)
-}
-
-// Percentiles computes all requested percentile values.
-func (h *runtimeHistogram) Percentiles(ps []float64) []float64 {
-	return h.load().Percentiles(ps)
-}
-
-// Max returns the highest sample value.
-func (h *runtimeHistogram) Max() int64 {
-	return h.load().Max()
-}
-
-// Min returns the lowest sample value.
-func (h *runtimeHistogram) Min() int64 {
-	return h.load().Min()
-}
-
-// Sum returns the sum of all sample values.
-func (h *runtimeHistogram) Sum() int64 {
-	return h.load().Sum()
-}
-
 type runtimeHistogramSnapshot metrics.Float64Histogram
 
-func (h *runtimeHistogramSnapshot) Clear() {
-	panic("runtimeHistogram does not support Clear")
-}
-func (h *runtimeHistogramSnapshot) Update(int64) {
-	panic("runtimeHistogram does not support Update")
-}
-func (h *runtimeHistogramSnapshot) Sample() Sample {
+func (h *runtimeHistogramSnapshot) Sample() SampleSnapshot {
 	return NilSample{}
 }
 
diff --git a/metrics/sample.go b/metrics/sample.go
index 252a878f58..42d3b61956 100644
--- a/metrics/sample.go
+++ b/metrics/sample.go
@@ -11,10 +11,7 @@ import (
 
 const rescaleThreshold = time.Hour
 
-// Samples maintain a statistically-significant selection of values from
-// a stream.
-type Sample interface {
-	Clear()
+type SampleSnapshot interface {
 	Count() int64
 	Max() int64
 	Mean() float64
@@ -22,14 +19,20 @@ type Sample interface {
 	Percentile(float64) float64
 	Percentiles([]float64) []float64
 	Size() int
-	Snapshot() Sample
 	StdDev() float64
 	Sum() int64
-	Update(int64)
 	Values() []int64
 	Variance() float64
 }
 
+// Samples maintain a statistically-significant selection of values from
+// a stream.
+type Sample interface {
+	Snapshot() SampleSnapshot
+	Clear()
+	Update(int64)
+}
+
 // ExpDecaySample is an exponentially-decaying sample using a forward-decaying
 // priority reservoir.  See Cormode et al's "Forward Decay: A Practical Time
 // Decay Model for Streaming Systems".
@@ -77,72 +80,16 @@ func (s *ExpDecaySample) Clear() {
 	s.values.Clear()
 }
 
-// Count returns the number of samples recorded, which may exceed the
-// reservoir size.
-func (s *ExpDecaySample) Count() int64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return s.count
-}
-
-// Max returns the maximum value in the sample, which may not be the maximum
-// value ever to be part of the sample.
-func (s *ExpDecaySample) Max() int64 {
-	return SampleMax(s.Values())
-}
-
-// Mean returns the mean of the values in the sample.
-func (s *ExpDecaySample) Mean() float64 {
-	return SampleMean(s.Values())
-}
-
-// Min returns the minimum value in the sample, which may not be the minimum
-// value ever to be part of the sample.
-func (s *ExpDecaySample) Min() int64 {
-	return SampleMin(s.Values())
-}
-
-// Percentile returns an arbitrary percentile of values in the sample.
-func (s *ExpDecaySample) Percentile(p float64) float64 {
-	return SamplePercentile(s.Values(), p)
-}
-
-// Percentiles returns a slice of arbitrary percentiles of values in the
-// sample.
-func (s *ExpDecaySample) Percentiles(ps []float64) []float64 {
-	return SamplePercentiles(s.Values(), ps)
-}
-
-// Size returns the size of the sample, which is at most the reservoir size.
-func (s *ExpDecaySample) Size() int {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return s.values.Size()
-}
-
 // Snapshot returns a read-only copy of the sample.
-func (s *ExpDecaySample) Snapshot() Sample {
+func (s *ExpDecaySample) Snapshot() SampleSnapshot {
 	s.mutex.Lock()
-	defer s.mutex.Unlock()
 	vals := s.values.Values()
 	values := make([]int64, len(vals))
 	for i, v := range vals {
 		values[i] = v.v
 	}
-	return &SampleSnapshot{
-		count:  s.count,
-		values: values,
-	}
-}
-
-// StdDev returns the standard deviation of the values in the sample.
-func (s *ExpDecaySample) StdDev() float64 {
-	return SampleStdDev(s.Values())
-}
-
-// Sum returns the sum of the values in the sample.
-func (s *ExpDecaySample) Sum() int64 {
-	return SampleSum(s.Values())
+	s.mutex.Unlock()
+	return newSampleSnapshot(s.count, values)
 }
 
 // Update samples a new value.
@@ -150,23 +97,6 @@ func (s *ExpDecaySample) Update(v int64) {
 	s.update(time.Now(), v)
 }
 
-// Values returns a copy of the values in the sample.
-func (s *ExpDecaySample) Values() []int64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	vals := s.values.Values()
-	values := make([]int64, len(vals))
-	for i, v := range vals {
-		values[i] = v.v
-	}
-	return values
-}
-
-// Variance returns the variance of the values in the sample.
-func (s *ExpDecaySample) Variance() float64 {
-	return SampleVariance(s.Values())
-}
-
 // update samples a new value at a particular timestamp.  This is a method all
 // its own to facilitate testing.
 func (s *ExpDecaySample) update(t time.Time, v int64) {
@@ -229,7 +159,7 @@ func (NilSample) Percentiles(ps []float64) []float64 {
 func (NilSample) Size() int { return 0 }
 
 // Sample is a no-op.
-func (NilSample) Snapshot() Sample { return NilSample{} }
+func (NilSample) Snapshot() SampleSnapshot { return NilSample{} }
 
 // StdDev is a no-op.
 func (NilSample) StdDev() float64 { return 0.0 }
@@ -246,42 +176,6 @@ func (NilSample) Values() []int64 { return []int64{} }
 // Variance is a no-op.
 func (NilSample) Variance() float64 { return 0.0 }
 
-// SampleMax returns the maximum value of the slice of int64.
-func SampleMax(values []int64) int64 {
-	if len(values) == 0 {
-		return 0
-	}
-	var max int64 = math.MinInt64
-	for _, v := range values {
-		if max < v {
-			max = v
-		}
-	}
-	return max
-}
-
-// SampleMean returns the mean value of the slice of int64.
-func SampleMean(values []int64) float64 {
-	if len(values) == 0 {
-		return 0.0
-	}
-	return float64(SampleSum(values)) / float64(len(values))
-}
-
-// SampleMin returns the minimum value of the slice of int64.
-func SampleMin(values []int64) int64 {
-	if len(values) == 0 {
-		return 0
-	}
-	var min int64 = math.MaxInt64
-	for _, v := range values {
-		if min > v {
-			min = v
-		}
-	}
-	return min
-}
-
 // SamplePercentiles returns an arbitrary percentile of the slice of int64.
 func SamplePercentile(values []int64, p float64) float64 {
 	return SamplePercentiles(values, []float64{p})[0]
@@ -310,99 +204,108 @@ func SamplePercentiles(values []int64, ps []float64) []float64 {
 	return scores
 }
 
-// SampleSnapshot is a read-only copy of another Sample.
-type SampleSnapshot struct {
+// sampleSnapshot is a read-only copy of another Sample.
+type sampleSnapshot struct {
 	count  int64
 	values []int64
+
+	max  int64
+	min  int64
+	mean float64
+	sum  int64
 }
 
-func NewSampleSnapshot(count int64, values []int64) *SampleSnapshot {
-	return &SampleSnapshot{
+// newSampleSnapshot creates a read-only sampleSnapShot, and calculates some
+// numbers.
+func newSampleSnapshot(count int64, values []int64) *sampleSnapshot {
+	s := &sampleSnapshot{
 		count:  count,
 		values: values,
 	}
-}
-
-// Clear panics.
-func (*SampleSnapshot) Clear() {
-	panic("Clear called on a SampleSnapshot")
+	if len(values) == 0 {
+		return s
+	}
+	var (
+		max int64 = math.MinInt64
+		min int64 = math.MaxInt64
+		sum int64
+	)
+	for _, v := range values {
+		sum += v
+		if v > max {
+			max = v
+		}
+		if v < min {
+			min = v
+		}
+	}
+	s.min = min
+	s.max = max
+	s.mean = float64(sum) / float64(len(values))
+	s.sum = sum
+	return s
 }
 
 // Count returns the count of inputs at the time the snapshot was taken.
-func (s *SampleSnapshot) Count() int64 { return s.count }
+func (s *sampleSnapshot) Count() int64 { return s.count }
 
 // Max returns the maximal value at the time the snapshot was taken.
-func (s *SampleSnapshot) Max() int64 { return SampleMax(s.values) }
+func (s *sampleSnapshot) Max() int64 { return s.max }
 
 // Mean returns the mean value at the time the snapshot was taken.
-func (s *SampleSnapshot) Mean() float64 { return SampleMean(s.values) }
+func (s *sampleSnapshot) Mean() float64 { return s.mean }
 
 // Min returns the minimal value at the time the snapshot was taken.
-func (s *SampleSnapshot) Min() int64 { return SampleMin(s.values) }
+func (s *sampleSnapshot) Min() int64 { return s.min }
 
 // Percentile returns an arbitrary percentile of values at the time the
 // snapshot was taken.
-func (s *SampleSnapshot) Percentile(p float64) float64 {
+func (s *sampleSnapshot) Percentile(p float64) float64 {
 	return SamplePercentile(s.values, p)
 }
 
 // Percentiles returns a slice of arbitrary percentiles of values at the time
 // the snapshot was taken.
-func (s *SampleSnapshot) Percentiles(ps []float64) []float64 {
+func (s *sampleSnapshot) Percentiles(ps []float64) []float64 {
 	return SamplePercentiles(s.values, ps)
 }
 
 // Size returns the size of the sample at the time the snapshot was taken.
-func (s *SampleSnapshot) Size() int { return len(s.values) }
+func (s *sampleSnapshot) Size() int { return len(s.values) }
 
 // Snapshot returns the snapshot.
-func (s *SampleSnapshot) Snapshot() Sample { return s }
+func (s *sampleSnapshot) Snapshot() SampleSnapshot { return s }
 
 // StdDev returns the standard deviation of values at the time the snapshot was
 // taken.
-func (s *SampleSnapshot) StdDev() float64 { return SampleStdDev(s.values) }
+func (s *sampleSnapshot) StdDev() float64 { return SampleStdDev(s.mean, s.values) }
 
 // Sum returns the sum of values at the time the snapshot was taken.
-func (s *SampleSnapshot) Sum() int64 { return SampleSum(s.values) }
-
-// Update panics.
-func (*SampleSnapshot) Update(int64) {
-	panic("Update called on a SampleSnapshot")
-}
+func (s *sampleSnapshot) Sum() int64 { return s.sum }
 
 // Values returns a copy of the values in the sample.
-func (s *SampleSnapshot) Values() []int64 {
+func (s *sampleSnapshot) Values() []int64 {
 	values := make([]int64, len(s.values))
 	copy(values, s.values)
 	return values
 }
 
 // Variance returns the variance of values at the time the snapshot was taken.
-func (s *SampleSnapshot) Variance() float64 { return SampleVariance(s.values) }
+func (s *sampleSnapshot) Variance() float64 { return SampleVariance(s.mean, s.values) }
 
 // SampleStdDev returns the standard deviation of the slice of int64.
-func SampleStdDev(values []int64) float64 {
-	return math.Sqrt(SampleVariance(values))
-}
-
-// SampleSum returns the sum of the slice of int64.
-func SampleSum(values []int64) int64 {
-	var sum int64
-	for _, v := range values {
-		sum += v
-	}
-	return sum
+func SampleStdDev(mean float64, values []int64) float64 {
+	return math.Sqrt(SampleVariance(mean, values))
 }
 
 // SampleVariance returns the variance of the slice of int64.
-func SampleVariance(values []int64) float64 {
+func SampleVariance(mean float64, values []int64) float64 {
 	if len(values) == 0 {
 		return 0.0
 	}
-	m := SampleMean(values)
 	var sum float64
 	for _, v := range values {
-		d := float64(v) - m
+		d := float64(v) - mean
 		sum += d * d
 	}
 	return sum / float64(len(values))
@@ -445,83 +348,13 @@ func (s *UniformSample) Clear() {
 	s.values = make([]int64, 0, s.reservoirSize)
 }
 
-// Count returns the number of samples recorded, which may exceed the
-// reservoir size.
-func (s *UniformSample) Count() int64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return s.count
-}
-
-// Max returns the maximum value in the sample, which may not be the maximum
-// value ever to be part of the sample.
-func (s *UniformSample) Max() int64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return SampleMax(s.values)
-}
-
-// Mean returns the mean of the values in the sample.
-func (s *UniformSample) Mean() float64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return SampleMean(s.values)
-}
-
-// Min returns the minimum value in the sample, which may not be the minimum
-// value ever to be part of the sample.
-func (s *UniformSample) Min() int64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return SampleMin(s.values)
-}
-
-// Percentile returns an arbitrary percentile of values in the sample.
-func (s *UniformSample) Percentile(p float64) float64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return SamplePercentile(s.values, p)
-}
-
-// Percentiles returns a slice of arbitrary percentiles of values in the
-// sample.
-func (s *UniformSample) Percentiles(ps []float64) []float64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return SamplePercentiles(s.values, ps)
-}
-
-// Size returns the size of the sample, which is at most the reservoir size.
-func (s *UniformSample) Size() int {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return len(s.values)
-}
-
 // Snapshot returns a read-only copy of the sample.
-func (s *UniformSample) Snapshot() Sample {
+func (s *UniformSample) Snapshot() SampleSnapshot {
 	s.mutex.Lock()
-	defer s.mutex.Unlock()
 	values := make([]int64, len(s.values))
 	copy(values, s.values)
-	return &SampleSnapshot{
-		count:  s.count,
-		values: values,
-	}
-}
-
-// StdDev returns the standard deviation of the values in the sample.
-func (s *UniformSample) StdDev() float64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return SampleStdDev(s.values)
-}
-
-// Sum returns the sum of the values in the sample.
-func (s *UniformSample) Sum() int64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return SampleSum(s.values)
+	s.mutex.Unlock()
+	return newSampleSnapshot(s.count, s.values)
 }
 
 // Update samples a new value.
@@ -544,22 +377,6 @@ func (s *UniformSample) Update(v int64) {
 	}
 }
 
-// Values returns a copy of the values in the sample.
-func (s *UniformSample) Values() []int64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	values := make([]int64, len(s.values))
-	copy(values, s.values)
-	return values
-}
-
-// Variance returns the variance of the values in the sample.
-func (s *UniformSample) Variance() float64 {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	return SampleVariance(s.values)
-}
-
 // expDecaySample represents an individual sample in a heap.
 type expDecaySample struct {
 	k float64
diff --git a/metrics/sample_test.go b/metrics/sample_test.go
index 3ae128d56f..018358d729 100644
--- a/metrics/sample_test.go
+++ b/metrics/sample_test.go
@@ -14,22 +14,29 @@ import (
 // computation for small samples and only slightly less for large samples.
 func BenchmarkCompute1000(b *testing.B) {
 	s := make([]int64, 1000)
+	var sum int64
 	for i := 0; i < len(s); i++ {
 		s[i] = int64(i)
+		sum += int64(i)
 	}
+	mean := float64(sum) / float64(len(s))
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		SampleVariance(s)
+		SampleVariance(mean, s)
 	}
 }
 func BenchmarkCompute1000000(b *testing.B) {
 	s := make([]int64, 1000000)
+	var sum int64
 	for i := 0; i < len(s); i++ {
 		s[i] = int64(i)
+		sum += int64(i)
+
 	}
+	mean := float64(sum) / float64(len(s))
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		SampleVariance(s)
+		SampleVariance(mean, s)
 	}
 }
 func BenchmarkCopy1000(b *testing.B) {