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opentelemetry-go/sdk/trace/sampling.go

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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.
package trace
import (
"encoding/binary"
"fmt"
"go.opentelemetry.io/otel/api/core"
api "go.opentelemetry.io/otel/api/trace"
)
// Sampler decides whether a trace should be sampled and exported.
type Sampler interface {
ShouldSample(SamplingParameters) SamplingResult
Description() string
}
// SamplingParameters contains the values passed to a Sampler.
type SamplingParameters struct {
ParentContext core.SpanContext
TraceID core.TraceID
SpanID core.SpanID
Name string
HasRemoteParent bool
Kind api.SpanKind
Attributes []core.KeyValue
Links []api.Link
}
// SamplingDecision indicates whether a span is recorded and sampled.
type SamplingDecision uint8
// Valid sampling decisions
const (
NotRecord SamplingDecision = iota
Record
RecordAndSampled
)
// SamplingResult conveys a SamplingDecision and a set of Attributes.
type SamplingResult struct {
Decision SamplingDecision
Attributes []core.KeyValue
}
type probabilitySampler struct {
traceIDUpperBound uint64
description string
}
func (ps probabilitySampler) ShouldSample(p SamplingParameters) SamplingResult {
if p.ParentContext.IsSampled() {
return SamplingResult{Decision: RecordAndSampled}
}
x := binary.BigEndian.Uint64(p.TraceID[0:8]) >> 1
if x < ps.traceIDUpperBound {
return SamplingResult{Decision: RecordAndSampled}
}
return SamplingResult{Decision: NotRecord}
}
func (ps probabilitySampler) Description() string {
return ps.description
}
// ProbabilitySampler samples a given fraction of traces. Fractions >= 1 will
// always sample. If the parent span is sampled, then it's child spans will
// automatically be sampled. Fractions < 0 are treated as zero, but spans may
// still be sampled if their parent is.
func ProbabilitySampler(fraction float64) Sampler {
if fraction >= 1 {
return AlwaysSample()
}
if fraction <= 0 {
fraction = 0
}
return &probabilitySampler{
traceIDUpperBound: uint64(fraction * (1 << 63)),
description: fmt.Sprintf("ProbabilitySampler{%g}", fraction),
}
}
type alwaysOnSampler struct{}
func (as alwaysOnSampler) ShouldSample(p SamplingParameters) SamplingResult {
return SamplingResult{Decision: RecordAndSampled}
}
func (as alwaysOnSampler) Description() string {
return "AlwaysOnSampler"
}
// AlwaysSample returns a Sampler that samples every trace.
// Be careful about using this sampler in a production application with
// significant traffic: a new trace will be started and exported for every
// request.
func AlwaysSample() Sampler {
return alwaysOnSampler{}
}
type alwaysOffSampler struct{}
func (as alwaysOffSampler) ShouldSample(p SamplingParameters) SamplingResult {
return SamplingResult{Decision: NotRecord}
}
func (as alwaysOffSampler) Description() string {
return "AlwaysOffSampler"
}
// NeverSample returns a Sampler that samples no traces.
func NeverSample() Sampler {
return alwaysOffSampler{}
}
// AlwaysParentSample returns a Sampler that samples a trace only
// if the parent span is sampled.
// This Sampler is a passthrough to the ProbabilitySampler with
// a fraction of value 0.
func AlwaysParentSample() Sampler {
return &probabilitySampler{
traceIDUpperBound: 0,
description: "AlwaysParentSampler",
}
}