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Add the experimental exemplar feature (#4871)
* Add the experimental exemplar feature * Add exemplars to EXPERIMENTAL.md * Add changelog entry * Fix hist buckets > 1 detection * Collect instead of Flush res about to be deleted * Add e2e test * Do not pre-alloc ResourceMetrics This only has a single use. * Fix grammatical error in comment * Add test cases Default and invalid OTEL_METRICS_EXEMPLAR_FILTER. Test sampled and non-sampled context for trace_based. * Comment nCPU * Doc OTEL_METRICS_EXEMPLAR_FILTER
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| Original file line number | Diff line number | Diff line change |
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| // Copyright The OpenTelemetry Authors | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
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| package metric // import "go.opentelemetry.io/otel/sdk/metric" | ||
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| import ( | ||
| "os" | ||
| "runtime" | ||
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| "go.opentelemetry.io/otel/sdk/metric/internal/exemplar" | ||
| "go.opentelemetry.io/otel/sdk/metric/internal/x" | ||
| ) | ||
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| // 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.Reservoir[N] { | ||
| if !x.Exemplars.Enabled() { | ||
| return nil | ||
| } | ||
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| // https://github.com/open-telemetry/opentelemetry-specification/blob/d4b241f451674e8f611bb589477680341006ad2b/specification/metrics/sdk.md#exemplar-defaults | ||
| resF := func() func() exemplar.Reservoir[N] { | ||
| // Explicit bucket histogram aggregation with more than 1 bucket will | ||
| // use AlignedHistogramBucketExemplarReservoir. | ||
| a, ok := agg.(AggregationExplicitBucketHistogram) | ||
| if ok && len(a.Boundaries) > 0 { | ||
| cp := make([]float64, len(a.Boundaries)) | ||
| copy(cp, a.Boundaries) | ||
| return func() exemplar.Reservoir[N] { | ||
| bounds := cp | ||
| return exemplar.Histogram[N](bounds) | ||
| } | ||
| } | ||
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| 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. numer 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 | ||
| } | ||
| } | ||
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| return func() exemplar.Reservoir[N] { | ||
| return exemplar.FixedSize[N](n) | ||
| } | ||
| } | ||
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| // https://github.com/open-telemetry/opentelemetry-specification/blob/d4b241f451674e8f611bb589477680341006ad2b/specification/configuration/sdk-environment-variables.md#exemplar | ||
| const filterEnvKey = "OTEL_METRICS_EXEMPLAR_FILTER" | ||
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| switch os.Getenv(filterEnvKey) { | ||
| case "always_on": | ||
| return resF() | ||
| case "always_off": | ||
| return exemplar.Drop[N] | ||
| case "trace_based": | ||
| fallthrough | ||
| default: | ||
| newR := resF() | ||
| return func() exemplar.Reservoir[N] { | ||
| return exemplar.SampledFilter(newR()) | ||
| } | ||
| } | ||
| } |
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