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Resolve https://github.com/open-telemetry/opentelemetry-go/issues/5249 ### Spec > exemplar_reservoir: A functional type that generates an exemplar reservoir a MeterProvider will use when storing exemplars. This functional type needs to be a factory or callback similar to aggregation selection functionality which allows different reservoirs to be chosen by the aggregation. > Users can provide an exemplar_reservoir, but it is up to their discretion. Therefore, the stream configuration parameter needs to be structured to accept an exemplar_reservoir, but MUST NOT obligate a user to provide one. If the user does not provide an exemplar_reservoir value, the MeterProvider MUST apply a [default exemplar reservoir](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#exemplar-defaults). Also, > the reservoir MUST be given the Attributes associated with its timeseries point either at construction so that additional sampling performed by the reservoir has access to all attributes from a measurement in the "offer" method. ### Changes In sdk/metric/exemplar, add: * `exemplar.ReservoirProvider` * `exemplar.HistogramReservoirProvider` * `exemplar.FixedSizeReservoirProvider` In sdk/metric, add: * `metric.ExemplarReservoirProviderSelector` (func Aggregation -> ReservoirProvider) * `metric.DefaultExemplarReservoirProviderSelector` (our default implementation) * `ExemplarReservoirProviderSelector` added to `metric.Stream` Note: the only required public types are `metric.ExemplarReservoirProviderSelector` and `ExemplarReservoirProviderSelector` in `metric.Stream`. Others are for convenience and readability. ### Alternatives considered #### Add ExemplarReservoirProvider directly to metric.Stream, instead of ExemplarReservoirProviderSelector This would mean users can configure a `func() exemplar.Reservoir` instead of a `func(Aggregation) func() exemplar.Reservoir`. I don't think this complies with the statement: `This functional type needs to be a factory or callback similar to aggregation selection functionality which allows different reservoirs to be chosen by the aggregation.`. I'm interpreting "allows different reservoirs to be chosen by the aggregation" as meaning "allows different reservoirs to be chosen **based on the** aggregation", rather than meaning that the aggregation is somehow choosing the reservoir. ### Future work There is some refactoring I plan to do after this to simplify the interaction between the internal/aggregate and exemplar package. I've omitted that from this PR to keep the diff smaller. --------- Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com> Co-authored-by: Robert Pająk <pellared@hotmail.com>
78 lines
3.1 KiB
Go
78 lines
3.1 KiB
Go
// Copyright The OpenTelemetry Authors
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// SPDX-License-Identifier: Apache-2.0
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package metric // import "go.opentelemetry.io/otel/sdk/metric"
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import (
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"runtime"
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"go.opentelemetry.io/otel/attribute"
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"go.opentelemetry.io/otel/sdk/metric/exemplar"
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"go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
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)
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// ExemplarReservoirProviderSelector selects the
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// [exemplar.ReservoirProvider] to use
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// based on the [Aggregation] of the metric.
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type ExemplarReservoirProviderSelector func(Aggregation) exemplar.ReservoirProvider
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// reservoirFunc returns the appropriately configured exemplar reservoir
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// creation func based on the passed InstrumentKind and filter configuration.
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func reservoirFunc[N int64 | float64](provider exemplar.ReservoirProvider, filter exemplar.Filter) func(attribute.Set) aggregate.FilteredExemplarReservoir[N] {
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return func(attrs attribute.Set) aggregate.FilteredExemplarReservoir[N] {
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return aggregate.NewFilteredExemplarReservoir[N](filter, provider(attrs))
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}
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}
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// DefaultExemplarReservoirProviderSelector returns the default
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// [exemplar.ReservoirProvider] for the
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// provided [Aggregation].
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//
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// For explicit bucket histograms with more than 1 bucket, it uses the
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// [exemplar.HistogramReservoirProvider].
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// For exponential histograms, it uses the
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// [exemplar.FixedSizeReservoirProvider]
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// with a size of min(20, max_buckets).
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// For all other aggregations, it uses the
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// [exemplar.FixedSizeReservoirProvider]
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// with a size equal to the number of CPUs.
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//
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// Exemplar default reservoirs MAY change in a minor version bump. No
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// guarantees are made on the shape or statistical properties of returned
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// exemplars.
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func DefaultExemplarReservoirProviderSelector(agg Aggregation) exemplar.ReservoirProvider {
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// https://github.com/open-telemetry/opentelemetry-specification/blob/d4b241f451674e8f611bb589477680341006ad2b/specification/metrics/sdk.md#exemplar-defaults
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// Explicit bucket histogram aggregation with more than 1 bucket will
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// use AlignedHistogramBucketExemplarReservoir.
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a, ok := agg.(AggregationExplicitBucketHistogram)
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if ok && len(a.Boundaries) > 0 {
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return exemplar.HistogramReservoirProvider(a.Boundaries)
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}
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var n int
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if a, ok := agg.(AggregationBase2ExponentialHistogram); ok {
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// Base2 Exponential Histogram Aggregation SHOULD use a
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// SimpleFixedSizeExemplarReservoir with a reservoir equal to the
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// smaller of the maximum number of buckets configured on the
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// aggregation or twenty (e.g. min(20, max_buckets)).
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n = int(a.MaxSize)
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if n > 20 {
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n = 20
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}
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} else {
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// https://github.com/open-telemetry/opentelemetry-specification/blob/e94af89e3d0c01de30127a0f423e912f6cda7bed/specification/metrics/sdk.md#simplefixedsizeexemplarreservoir
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// This Exemplar reservoir MAY take a configuration parameter for
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// the size of the reservoir. If no size configuration is
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// provided, the default size MAY be the number of possible
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// concurrent threads (e.g. number of CPUs) to help reduce
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// contention. Otherwise, a default size of 1 SHOULD be used.
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n = runtime.NumCPU()
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if n < 1 {
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// Should never be the case, but be defensive.
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n = 1
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}
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}
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return exemplar.FixedSizeReservoirProvider(n)
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}
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