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