/
sampler.go
84 lines (74 loc) · 2.18 KB
/
sampler.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
// Unless explicitly stated otherwise all files in this repository are licensed
// under the Apache License Version 2.0.
// This product includes software developed at Datadog (https://www.datadog.com/).
// Copyright 2018 Datadog, Inc.
package datadog
import (
"encoding/json"
"io"
"math"
"sync"
"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/ext"
)
// constants used for the Knuth hashing, same as agent.
const knuthFactor = uint64(1111111111111111111)
// sampledByRate verifies if the number n should be sampled at the specified
// rate.
func sampledByRate(n uint64, rate float64) bool {
if rate < 1 {
return n*knuthFactor < uint64(rate*math.MaxUint64)
}
return true
}
// prioritySampler holds a set of per-service sampling rates and applies
// them to spans.
type prioritySampler struct {
mu sync.RWMutex
rates map[string]float64
defaultRate float64
}
func newPrioritySampler() *prioritySampler {
return &prioritySampler{
rates: make(map[string]float64),
defaultRate: 1.,
}
}
// readRatesJSON will try to read the rates as JSON from the given io.ReadCloser.
func (ps *prioritySampler) readRatesJSON(rc io.ReadCloser) error {
var payload struct {
Rates map[string]float64 `json:"rate_by_service"`
}
if err := json.NewDecoder(rc).Decode(&payload); err != nil {
return err
}
rc.Close()
const defaultRateKey = "service:,env:"
ps.mu.Lock()
defer ps.mu.Unlock()
ps.rates = payload.Rates
if v, ok := ps.rates[defaultRateKey]; ok {
ps.defaultRate = v
delete(ps.rates, defaultRateKey)
}
return nil
}
// getRate returns the sampling rate to be used for the given span.
func (ps *prioritySampler) getRate(spn *ddSpan) float64 {
key := "service:" + spn.Service + ",env:" + spn.Meta[ext.Environment]
ps.mu.RLock()
defer ps.mu.RUnlock()
if rate, ok := ps.rates[key]; ok {
return rate
}
return ps.defaultRate
}
// applyPriority applies sampling priority to the given ddSpan.
func (ps *prioritySampler) applyPriority(spn *ddSpan) {
rate := ps.getRate(spn)
if sampledByRate(spn.TraceID, rate) {
spn.Metrics[keySamplingPriority] = ext.PriorityAutoKeep
} else {
spn.Metrics[keySamplingPriority] = ext.PriorityAutoReject
}
spn.Metrics[keySamplingPriorityRate] = rate
}