sampling.go

Documentation: go.opencensus.io/trace

     1  // Copyright 2017, OpenCensus Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package trace
    16  
    17  import (
    18  	"encoding/binary"
    19  )
    20  
    21  const defaultSamplingProbability = 1e-4
    22  
    23  // Sampler decides whether a trace should be sampled and exported.
    24  type Sampler func(SamplingParameters) SamplingDecision
    25  
    26  // SamplingParameters contains the values passed to a Sampler.
    27  type SamplingParameters struct {
    28  	ParentContext   SpanContext
    29  	TraceID         TraceID
    30  	SpanID          SpanID
    31  	Name            string
    32  	HasRemoteParent bool
    33  }
    34  
    35  // SamplingDecision is the value returned by a Sampler.
    36  type SamplingDecision struct {
    37  	Sample bool
    38  }
    39  
    40  // ProbabilitySampler returns a Sampler that samples a given fraction of traces.
    41  //
    42  // It also samples spans whose parents are sampled.
    43  func ProbabilitySampler(fraction float64) Sampler {
    44  	if !(fraction >= 0) {
    45  		fraction = 0
    46  	} else if fraction >= 1 {
    47  		return AlwaysSample()
    48  	}
    49  
    50  	traceIDUpperBound := uint64(fraction * (1 << 63))
    51  	return Sampler(func(p SamplingParameters) SamplingDecision {
    52  		if p.ParentContext.IsSampled() {
    53  			return SamplingDecision{Sample: true}
    54  		}
    55  		x := binary.BigEndian.Uint64(p.TraceID[0:8]) >> 1
    56  		return SamplingDecision{Sample: x < traceIDUpperBound}
    57  	})
    58  }
    59  
    60  // AlwaysSample returns a Sampler that samples every trace.
    61  // Be careful about using this sampler in a production application with
    62  // significant traffic: a new trace will be started and exported for every
    63  // request.
    64  func AlwaysSample() Sampler {
    65  	return func(p SamplingParameters) SamplingDecision {
    66  		return SamplingDecision{Sample: true}
    67  	}
    68  }
    69  
    70  // NeverSample returns a Sampler that samples no traces.
    71  func NeverSample() Sampler {
    72  	return func(p SamplingParameters) SamplingDecision {
    73  		return SamplingDecision{Sample: false}
    74  	}
    75  }
    76
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