sampler

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Published: Oct 16, 2018 License: BSD-3-Clause Imports: 12 Imported by: 0

Documentation

Overview

Package sampler contains all the logic of the agent-side trace sampling

Currently implementation is based on the scoring of the "signature" of each trace Based on the score, we get a sample rate to apply to the given trace

Current score implementation is super-simple, it is a counter with polynomial decay per signature. We increment it for each incoming trace then we periodically divide the score by two every X seconds. Right after the division, the score is an approximation of the number of received signatures over X seconds. It is different from the scoring in the Agent.

Since the sampling can happen at different levels (client, agent, server) or depending on different rules, we have to track the sample rate applied at previous steps. This way, sampling twice at 50% can result in an effective 25% sampling. The rate is stored as a metric in the trace root.

Package sampler contains all the logic of the agent-side trace sampling

Currently implementation is based on the scoring of the "signature" of each trace Based on the score, we get a sample rate to apply to the given trace

Current score implementation is super-simple, it is a counter with polynomial decay per signature. We increment it for each incoming trace then we periodically divide the score by two every X seconds. Right after the division, the score is an approximation of the number of received signatures over X seconds. It is different from the scoring in the Agent.

Since the sampling can happen at different levels (client, agent, server) or depending on different rules, we have to track the sample rate applied at previous steps. This way, sampling twice at 50% can result in an effective 25% sampling. The rate is stored as a metric in the trace root.

Package sampler contains all the logic of the agent-side trace sampling

Currently implementation is based on the scoring of the "signature" of each trace Based on the score, we get a sample rate to apply to the given trace

Current score implementation is super-simple, it is a counter with polynomial decay per signature. We increment it for each incoming trace then we periodically divide the score by two every X seconds. Right after the division, the score is an approximation of the number of received signatures over X seconds. It is different from the scoring in the Agent.

Since the sampling can happen at different levels (client, agent, server) or depending on different rules, we have to track the sample rate applied at previous steps. This way, sampling twice at 50% can result in an effective 25% sampling. The rate is stored as a metric in the trace root.

Index

Constants

View Source
const (
	// SamplingPriorityKey is the key of the sampling priority value in the metrics map of the root span
	SamplingPriorityKey = "_sampling_priority_v1"
)
View Source
const (
	// TraceCountHeader is the header client implementation should fill
	// with the number of traces contained in the payload.
	TraceCountHeader = "X-Datadog-Trace-Count"
)

Variables

This section is empty.

Functions

func CalcPreSampleRate

func CalcPreSampleRate(maxUserAvg, currentUserAvg, currentRate float64) (float64, error)

CalcPreSampleRate gives the new sample rate to apply for a given max user CPU average. It takes the current sample rate and user CPU average as those parameters both have an influence on the result.

func GetTraceAppliedSampleRate

func GetTraceAppliedSampleRate(root *model.Span) float64

GetTraceAppliedSampleRate gets the sample rate the sample rate applied earlier in the pipeline.

func SampleByRate

func SampleByRate(traceID uint64, sampleRate float64) bool

SampleByRate tells if a trace (from its ID) with a given rate should be sampled Use Knuth multiplicative hashing to leverage imbalanced traceID generators

func SetTraceAppliedSampleRate

func SetTraceAppliedSampleRate(root *model.Span, sampleRate float64)

SetTraceAppliedSampleRate sets the currently applied sample rate in the trace data to allow chained up sampling.

Types

type Backend

type Backend interface {
	// Run runs the blocking execution of the backend main loop.
	Run()

	// Stop stops the backend main loop.
	Stop()

	// CountSample counts that 1 trace is going through the sampler.
	CountSample()

	// CountSignature counts that 1 signature is going through the sampler.
	CountSignature(signature Signature)

	// GetTotalScore returns the TPS (Traces Per Second) of all traces ingested.
	GetTotalScore() float64

	// GetSampledScore returns the TPS of all traces sampled.
	GetSampledScore() float64

	// GetUpperSampledScore is similar to GetSampledScore, but with the upper approximation.
	GetUpperSampledScore() float64

	// GetSignatureScore returns the TPS of traces ingested of a given signature.
	GetSignatureScore(signature Signature) float64

	// GetSignatureScores returns the TPS of traces ingested for all signatures.
	GetSignatureScores() map[Signature]float64

	// GetCardinality returns the number of different signatures seen.
	GetCardinality() int64
}

Backend stores and counts traces and signatures ingested by a sampler.

type Engine

type Engine interface {
	// Run the sampler.
	Run()
	// Stop the sampler.
	Stop()
	// Sample a trace.
	Sample(trace model.Trace, root *model.Span, env string) bool
	// GetState returns information about the sampler.
	GetState() interface{}
	// GetType returns the type of the sampler.
	GetType() EngineType
}

Engine is a common basic interface for sampler engines.

type EngineType

type EngineType int

EngineType represents the type of a sampler engine.

const (
	// NormalScoreEngineType is the type of the ScoreEngine sampling non-error traces.
	NormalScoreEngineType EngineType = iota
	// ErrorsScoreEngineType is the type of the ScoreEngine sampling error traces.
	ErrorsScoreEngineType
	// PriorityEngineType is type of the priority sampler engine type.
	PriorityEngineType
)

type InternalState

type InternalState struct {
	Offset      float64
	Slope       float64
	Cardinality int64
	InTPS       float64
	OutTPS      float64
	MaxTPS      float64
}

InternalState exposes all the main internal settings of the score sampler

type MemoryBackend

type MemoryBackend struct {
	// contains filtered or unexported fields
}

MemoryBackend storing any state required to run the sampling algorithms.

Current implementation is only based on counters with polynomial decay. Its bias with steady counts is 1 * decayFactor. The stored scores represent approximation of the real count values (with a countScaleFactor factor).

func NewMemoryBackend

func NewMemoryBackend(decayPeriod time.Duration, decayFactor float64) *MemoryBackend

NewMemoryBackend returns an initialized Backend.

func (*MemoryBackend) CountSample

func (b *MemoryBackend) CountSample()

CountSample counts a trace sampled by the sampler.

func (*MemoryBackend) CountSignature

func (b *MemoryBackend) CountSignature(signature Signature)

CountSignature counts an incoming signature.

func (*MemoryBackend) GetCardinality

func (b *MemoryBackend) GetCardinality() int64

GetCardinality returns the number of different signatures seen recently.

func (*MemoryBackend) GetSampledScore

func (b *MemoryBackend) GetSampledScore() float64

GetSampledScore returns the global score of all sampled traces.

func (*MemoryBackend) GetSignatureScore

func (b *MemoryBackend) GetSignatureScore(signature Signature) float64

GetSignatureScore returns the score of a signature. It is normalized to represent a number of signatures per second.

func (*MemoryBackend) GetSignatureScores

func (b *MemoryBackend) GetSignatureScores() map[Signature]float64

GetSignatureScores returns the scores for all signatures. It is normalized to represent a number of signatures per second.

func (*MemoryBackend) GetTotalScore

func (b *MemoryBackend) GetTotalScore() float64

GetTotalScore returns the global score of all sampled traces.

func (*MemoryBackend) GetUpperSampledScore

func (b *MemoryBackend) GetUpperSampledScore() float64

GetUpperSampledScore returns a certain upper bound of the global count of all sampled traces.

func (*MemoryBackend) Run

func (b *MemoryBackend) Run()

Run runs and block on the Sampler main loop.

func (*MemoryBackend) Stop

func (b *MemoryBackend) Stop()

Stop stops the main Run loop.

type PreSampler

type PreSampler struct {
	// contains filtered or unexported fields
}

PreSampler tries to tell wether we should keep a payload, even before fully processing it. Its only clues are the unparsed payload and the HTTP headers. It should remain very light and fast.

func NewPreSampler

func NewPreSampler() *PreSampler

NewPreSampler returns an initialized presampler

func (*PreSampler) Rate

func (ps *PreSampler) Rate() float64

Rate returns the current target pre-sample rate, thread-safe. The target pre-sample rate is the value set with SetRate, ideally this is the sample rate, but depending on what is received, the real rate might defer.

func (*PreSampler) RealRate

func (ps *PreSampler) RealRate() float64

RealRate returns the current real pre-sample rate, thread-safe. This is the value obtained by counting what was kept and dropped.

func (*PreSampler) Run

func (ps *PreSampler) Run()

Run runs and block on the Sampler main loop

func (*PreSampler) Sample

func (ps *PreSampler) Sample(req *http.Request) bool

Sample tells wether a given request should be kept (true means: "yes, keep it"). Calling this alters the statistics, it affects the result of RealRate() so only call it once per payload.

func (*PreSampler) SetError

func (ps *PreSampler) SetError(err error)

SetError set the pre-sample error, thread-safe.

func (*PreSampler) SetRate

func (ps *PreSampler) SetRate(rate float64)

SetRate set the pre-sample rate, thread-safe.

func (*PreSampler) Stats

func (ps *PreSampler) Stats() *PreSamplerStats

Stats returns a copy of the currrent pre-sampler stats.

func (*PreSampler) Stop

func (ps *PreSampler) Stop()

Stop stops the main Run loop

type PreSamplerStats

type PreSamplerStats struct {
	// Rate is the target pre-sampling rate.
	Rate float64
	// Error is the last error got when trying to calc the pre-sampling rate.
	// Stored as a string as this is easier to marshal & publish in JSON.
	Error string
	// RecentPayloadsSeen is the number of payloads that passed by.
	RecentPayloadsSeen float64
	// RecentTracesSeen is the number of traces that passed by.
	RecentTracesSeen float64
	// RecentTracesDropped is the number of traces that were dropped.
	RecentTracesDropped float64
}

PreSamplerStats contains pre-sampler data. The public content might be interesting for statistics, logging.

func (*PreSamplerStats) RealRate

func (stats *PreSamplerStats) RealRate() float64

RealRate calcuates the current real pre-sample rate from the stats data. If no data is available, returns the target rate.

type PriorityEngine

type PriorityEngine struct {
	// Sampler is the underlying sampler used by this engine, sharing logic among various engines.
	Sampler *Sampler
	// contains filtered or unexported fields
}

PriorityEngine is the main component of the sampling logic

func NewPriorityEngine

func NewPriorityEngine(extraRate float64, maxTPS float64, rateByService *config.RateByService) *PriorityEngine

NewPriorityEngine returns an initialized Sampler

func (*PriorityEngine) GetState

func (s *PriorityEngine) GetState() interface{}

GetState collects and return internal statistics and coefficients for indication purposes It returns an interface{}, as other samplers might return other informations.

func (*PriorityEngine) GetType

func (s *PriorityEngine) GetType() EngineType

GetType return the type of the sampler engine

func (*PriorityEngine) Run

func (s *PriorityEngine) Run()

Run runs and block on the Sampler main loop

func (*PriorityEngine) Sample

func (s *PriorityEngine) Sample(trace model.Trace, root *model.Span, env string) bool

Sample counts an incoming trace and tells if it is a sample which has to be kept

func (*PriorityEngine) Stop

func (s *PriorityEngine) Stop()

Stop stops the main Run loop

type Sampler

type Sampler struct {
	// Storage of the state of the sampler
	Backend Backend
	// contains filtered or unexported fields
}

Sampler is the main component of the sampling logic

func (*Sampler) AdjustScoring

func (s *Sampler) AdjustScoring()

AdjustScoring modifies sampler coefficients to fit better the `maxTPS` condition

func (*Sampler) GetAllCountScores

func (s *Sampler) GetAllCountScores() map[Signature]float64

GetAllCountScores scores all signatures based on their recent throughput The score value can be seeing as the sample rate if the count were the only factor Since other factors can intervene (such as extra global sampling), its value can be larger than 1

func (*Sampler) GetAllSignatureSampleRates

func (s *Sampler) GetAllSignatureSampleRates() map[Signature]float64

GetAllSignatureSampleRates gives the sample rate to apply to all signatures. For now, only based on count score.

func (*Sampler) GetCountScore

func (s *Sampler) GetCountScore(signature Signature) float64

GetCountScore scores any signature based on its recent throughput The score value can be seeing as the sample rate if the count were the only factor Since other factors can intervene (such as extra global sampling), its value can be larger than 1

func (*Sampler) GetDefaultCountScore

func (s *Sampler) GetDefaultCountScore() float64

GetDefaultCountScore returns a default score when not knowing the signature for real. Since other factors can intervene (such as extra global sampling), its value can be larger than 1

func (*Sampler) GetDefaultSampleRate

func (s *Sampler) GetDefaultSampleRate() float64

GetDefaultSampleRate gives the sample rate to apply to an unknown signature. For now, only based on count score.

func (*Sampler) GetMaxTPSSampleRate

func (s *Sampler) GetMaxTPSSampleRate() float64

GetMaxTPSSampleRate returns an extra sample rate to apply if we are above maxTPS.

func (*Sampler) GetSampleRate

func (s *Sampler) GetSampleRate(trace model.Trace, root *model.Span, signature Signature) float64

GetSampleRate returns the sample rate to apply to a trace.

func (*Sampler) GetSignatureSampleRate

func (s *Sampler) GetSignatureSampleRate(signature Signature) float64

GetSignatureSampleRate gives the sample rate to apply to any signature. For now, only based on count score.

func (*Sampler) GetState

func (s *Sampler) GetState() InternalState

GetState collects and return internal statistics and coefficients for indication purposes

func (*Sampler) Run

func (s *Sampler) Run()

Run runs and block on the Sampler main loop

func (*Sampler) RunAdjustScoring

func (s *Sampler) RunAdjustScoring()

RunAdjustScoring is the sampler feedback loop to adjust the scoring coefficients

func (*Sampler) SetSignatureCoefficients

func (s *Sampler) SetSignatureCoefficients(offset float64, slope float64)

SetSignatureCoefficients updates the internal scoring coefficients used by the signature scoring

func (*Sampler) Stop

func (s *Sampler) Stop()

Stop stops the main Run loop

func (*Sampler) UpdateExtraRate

func (s *Sampler) UpdateExtraRate(extraRate float64)

UpdateExtraRate updates the extra sample rate

func (*Sampler) UpdateMaxTPS

func (s *Sampler) UpdateMaxTPS(maxTPS float64)

UpdateMaxTPS updates the max TPS limit

type ScoreEngine

type ScoreEngine struct {
	// Sampler is the underlying sampler used by this engine, sharing logic among various engines.
	Sampler *Sampler
	// contains filtered or unexported fields
}

ScoreEngine is the main component of the sampling logic

func NewErrorsEngine

func NewErrorsEngine(extraRate float64, maxTPS float64) *ScoreEngine

NewErrorsEngine returns an initialized Sampler dedicate to errors. It behaves just like the the normal ScoreEngine except for its GetType method (useful for reporting).

func NewScoreEngine

func NewScoreEngine(extraRate float64, maxTPS float64) *ScoreEngine

NewScoreEngine returns an initialized Sampler

func (*ScoreEngine) GetState

func (s *ScoreEngine) GetState() interface{}

GetState collects and return internal statistics and coefficients for indication purposes It returns an interface{}, as other samplers might return other informations.

func (*ScoreEngine) GetType

func (s *ScoreEngine) GetType() EngineType

GetType returns the type of the sampler

func (*ScoreEngine) Run

func (s *ScoreEngine) Run()

Run runs and block on the Sampler main loop

func (*ScoreEngine) Sample

func (s *ScoreEngine) Sample(trace model.Trace, root *model.Span, env string) bool

Sample counts an incoming trace and tells if it is a sample which has to be kept

func (*ScoreEngine) Stop

func (s *ScoreEngine) Stop()

Stop stops the main Run loop

type Signature

type Signature uint64

Signature is a simple representation of trace, used to identify simlar traces

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