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// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0
package metric // import "go.opentelemetry.io/otel/sdk/metric"
import (
"os"
"runtime"
"slices"
"go.opentelemetry.io/otel/sdk/metric/internal/exemplar"
"go.opentelemetry.io/otel/sdk/metric/internal/x"
)
// reservoirFunc returns the appropriately configured exemplar reservoir
// creation func based on the passed InstrumentKind and user defined
// environment variables.
//
// 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[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/configuration/sdk-environment-variables.md#exemplar
const filterEnvKey = "OTEL_METRICS_EXEMPLAR_FILTER"
var filter exemplar.Filter
switch os.Getenv(filterEnvKey) {
case "always_on":
filter = exemplar.AlwaysOnFilter
case "always_off":
return exemplar.Drop
case "trace_based":
fallthrough
default:
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))
}
}
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