sampler

package
v0.0.0-...-7983b3b Latest Latest
Warning

This package is not in the latest version of its module.

 Go to latest Published: Apr 8, 2024 License: Apache-2.0 Imports: 19 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.

Index

Constants

View Source 
const (
	// KeySamplingRateGlobal is a metric key holding the global sampling rate.
	KeySamplingRateGlobal = "_sample_rate"

	// KeySamplingRateClient is a metric key holding the client-set sampling rate for APM events.
	KeySamplingRateClient = "_dd1.sr.rcusr"

	// KeySamplingRatePreSampler is a metric key holding the API rate limiter's rate for APM events.
	KeySamplingRatePreSampler = "_dd1.sr.rapre"

	// KeySamplingRateEventExtraction is the key of the metric storing the event extraction rate on an APM event.
	KeySamplingRateEventExtraction = "_dd1.sr.eausr"

	// KeySamplingRateMaxEPSSampler is the key of the metric storing the max eps sampler rate on an APM event.
	KeySamplingRateMaxEPSSampler = "_dd1.sr.eamax"

	// KeyErrorType is the key of the error type in the meta map
	KeyErrorType = "error.type"

	// KeyAnalyzedSpans is the metric key which specifies if a span is analyzed.
	KeyAnalyzedSpans = "_dd.analyzed"

	// KeyHTTPStatusCode is the key of the http status code in the meta map
	KeyHTTPStatusCode = "http.status_code"
)

Variables

This section is empty.

Functions

func GetClientRate 

func GetClientRate(s *pb.Span) float64

GetClientRate gets the rate at which the trace this span belongs to was sampled by the tracer. NOTE: This defaults to 1 if no rate is stored.

func GetEventExtractionRate 

func GetEventExtractionRate(s *pb.Span) float64

GetEventExtractionRate gets the rate at which the trace from which we extracted this event was sampled at the tracer. This defaults to 1 if no rate is stored.

func GetGlobalRate 

func GetGlobalRate(s *pb.Span) float64

GetGlobalRate gets the cumulative sample rate of the trace to which this span belongs to.

func GetMaxEPSRate 

func GetMaxEPSRate(s *pb.Span) float64

GetMaxEPSRate gets the rate at which this event was sampled by the max eps event sampler.

func GetPreSampleRate 

func GetPreSampleRate(s *pb.Span) float64

GetPreSampleRate returns the rate at which the trace this span belongs to was sampled by the agent's presampler. NOTE: This defaults to 1 if no rate is stored.

func IsAnalyzedSpan 

func IsAnalyzedSpan(s *pb.Span) bool

IsAnalyzedSpan checks if a span is analyzed

func SampleByRate 

func SampleByRate(traceID uint64, rate 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 SetAnalyzedSpan 

func SetAnalyzedSpan(s *pb.Span)

SetAnalyzedSpan marks a span analyzed

func SetClientRate 

func SetClientRate(s *pb.Span, rate float64)

SetClientRate sets the rate at which the trace this span belongs to was sampled by the tracer.

func SetEventExtractionRate 

func SetEventExtractionRate(s *pb.Span, rate float64)

SetEventExtractionRate sets the rate at which the trace from which we extracted this event was sampled at the tracer.

func SetMaxEPSRate 

func SetMaxEPSRate(s *pb.Span, rate float64)

SetMaxEPSRate sets the rate at which this event was sampled by the max eps event sampler.

func SetPreSampleRate 

func SetPreSampleRate(s *pb.Span, rate float64)

SetPreSampleRate sets the rate at which the trace this span belongs to was sampled by the agent's presampler.

Types

type DynamicConfig 

type DynamicConfig struct {
	// RateByService contains the rate for each service/env tuple,
	// used in priority sampling by client libs.
	RateByService RateByService
}

DynamicConfig contains configuration items which may change dynamically over time.

func NewDynamicConfig 

func NewDynamicConfig(env string) *DynamicConfig

NewDynamicConfig creates a new dynamic config object which maps service signatures to their corresponding sampling rates. Each service will have a default assigned matching the service rate of the specified env.

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 ErrorsSampler 

type ErrorsSampler struct{ ScoreSampler }

ErrorsSampler is dedicated to catching traces containing spans with errors.

func NewErrorsSampler 

func NewErrorsSampler(conf *config.AgentConfig) *ErrorsSampler

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

type MemoryBackend 

type MemoryBackend struct {

	// DecayPeriod is the time period between each score decay.
	// A lower value is more reactive, but forgets quicker.
	DecayPeriod time.Duration
	// 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) AddTotalScore 

func (b *MemoryBackend) AddTotalScore(n float64)

AddTotalScore adds to the total score.

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) CountWeightedSig 

func (b *MemoryBackend) CountWeightedSig(signature Signature, n float64)

CountWeightedSig counts a trace sampled by the sampler.

func (*MemoryBackend) DecayScore 

func (b *MemoryBackend) DecayScore()

DecayScore applies the decay to the rolling counters.

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.

type NoPrioritySampler 

type NoPrioritySampler struct{ ScoreSampler }

NoPrioritySampler is dedicated to catching traces with no priority set.

func NewNoPrioritySampler 

func NewNoPrioritySampler(conf *config.AgentConfig) *NoPrioritySampler

NewNoPrioritySampler returns an initialized Sampler dedicated to traces with no priority set.

type PrioritySampler 

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

PrioritySampler computes priority rates per env, service to apply in a feedback loop with trace-agent clients. Computed rates are sent in http responses to trace-agent. The rates are continuously adjusted in function of the received traffic to match a targetTPS (target traces per second). In order of priority, the sampler will match a targetTPS set remotely (remoteRates) and then the local targetTPS.

func NewPrioritySampler 

func NewPrioritySampler(conf *config.AgentConfig, dynConf *DynamicConfig) *PrioritySampler

NewPrioritySampler returns an initialized Sampler

func (*PrioritySampler) CountClientDroppedP0s 

func (s *PrioritySampler) CountClientDroppedP0s(dropped int64)

CountClientDroppedP0s counts client dropped traces. They are added to the totalScore, allowing them to weight on sampling rates during adjust calls

func (*PrioritySampler) CountSampled 

func (s *PrioritySampler) CountSampled(root *pb.Span, clientDroppedP0s bool, signature Signature, rate float64)

CountSampled counts sampled chunks with local chunk root signature.

func (*PrioritySampler) CountSignature 

func (s *PrioritySampler) CountSignature(root *pb.Span, signature Signature)

CountSignature counts all chunks received with local chunk root signature.

func (*PrioritySampler) Sample 

func (s *PrioritySampler) Sample(trace *pb.TraceChunk, root *pb.Span, env string, clientDroppedP0s bool) bool

Sample counts an incoming trace and returns the trace sampling decision and the applied sampling rate

func (*PrioritySampler) Start 

func (s *PrioritySampler) Start()

Start runs and block on the Sampler main loop

func (*PrioritySampler) Stop 

func (s *PrioritySampler) Stop()

Stop stops the sampler main loop

type RareSampler 

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

RareSampler samples traces that are not caught by the Priority sampler. It ensures that we sample traces for each combination of (env, service, name, resource, error type, http status) seen on a top level or measured span for which we did not see any span with a priority > 0 (sampled by Priority). The resulting sampled traces will likely be incomplete and will be flagged with a exceptioKey metric set at 1.

func NewRareSampler 

func NewRareSampler() *RareSampler

NewRareSampler returns a NewRareSampler that ensures that we sample combinations of env, service, name, resource, http-status, error type for each top level or measured spans

func (*RareSampler) Sample 

func (e *RareSampler) Sample(t *pb.TraceChunk, env string) bool

Sample a trace and returns true if trace was sampled (should be kept)

func (*RareSampler) Stop 

func (e *RareSampler) Stop()

Stop stops reporting stats

type RateByService 

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

RateByService stores the sampling rate per service. It is thread-safe, so one can read/write on it concurrently, using getters and setters.

func (*RateByService) GetAll 

func (rbs *RateByService) GetAll() map[string]float64

GetAll returns all sampling rates for all services.

func (*RateByService) SetAll 

func (rbs *RateByService) SetAll(rates map[ServiceSignature]float64)

SetAll the sampling rate for all services. If a service/env is not in the map, then the entry is removed.

type RemoteRates 

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

RemoteRates computes rates per (env, service) to apply in trace-agent clients. The rates are adjusted to match a targetTPS per (env, service) received from remote configurations. RemoteRates listens for new remote configurations with a grpc subscriber. On reception, new tps targets replace the previous ones.

func (*RemoteRates) AdjustScoring 

func (r *RemoteRates) AdjustScoring()

AdjustScoring adjust scores of all samplers

func (*RemoteRates) CountSample 

func (r *RemoteRates) CountSample(root *pb.Span, sig Signature)

CountSample counts the number of sampled root span matching a signature.

func (*RemoteRates) CountSignature 

func (r *RemoteRates) CountSignature(sig Signature)

CountSignature counts the number of root span seen matching a signature.

func (*RemoteRates) CountWeightedSig 

func (r *RemoteRates) CountWeightedSig(sig Signature, weight float64)

CountWeightedSig counts weighted root span seen for a signature. This function is called when trace-agent client drop unsampled spans. as dropped root spans are not accounted anymore in CountSignature calls.

func (*RemoteRates) DecayScores 

func (r *RemoteRates) DecayScores()

DecayScores decays scores of all samplers

func (*RemoteRates) GetAllSignatureSampleRates 

func (r *RemoteRates) GetAllSignatureSampleRates() map[Signature]float64

GetAllSignatureSampleRates returns sampling rates to apply for all registered signatures.

func (*RemoteRates) GetSignatureSampleRate 

func (r *RemoteRates) GetSignatureSampleRate(sig Signature) (float64, bool)

GetSignatureSampleRate returns the sampling rate to apply for a registered signature.

func (*RemoteRates) Start 

func (r *RemoteRates) Start()

Start runs and adjust rates per signature following remote TPS targets

func (*RemoteRates) Stop 

func (r *RemoteRates) Stop()

Stop stops RemoteRates main loop

type Sampler 

type Sampler struct {
	// Storage of the state of the sampler
	Backend *MemoryBackend
	// 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 `targetTPS` 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) GetSampleRate 

func (s *Sampler) GetSampleRate(trace pb.Trace, root *pb.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) GetTargetTPSSampleRate 

func (s *Sampler) GetTargetTPSSampleRate() float64

GetTargetTPSSampleRate returns an extra sample rate to apply if we are above targetTPS.

func (*Sampler) SetSignatureCoefficients 

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

SetSignatureCoefficients updates the internal scoring coefficients used by the signature scoring

func (*Sampler) Start 

func (s *Sampler) Start()

Start runs and the Sampler main loop

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) UpdateTargetTPS 

func (s *Sampler) UpdateTargetTPS(targetTPS float64)

UpdateTargetTPS updates the max TPS limit

type SamplingPriority 

type SamplingPriority int8

SamplingPriority is the type encoding a priority sampling decision. 

const (
	// PriorityNone is the value for SamplingPriority when no priority sampling decision could be found.
	PriorityNone SamplingPriority = math.MinInt8

	// PriorityUserDrop is the value set by a user to explicitly drop a trace.
	PriorityUserDrop SamplingPriority = -1

	// PriorityAutoDrop is the value set by a tracer to suggest dropping a trace.
	PriorityAutoDrop SamplingPriority = 0

	// PriorityAutoKeep is the value set by a tracer to suggest keeping a trace.
	PriorityAutoKeep SamplingPriority = 1

	// PriorityUserKeep is the value set by a user to explicitly keep a trace.
	PriorityUserKeep SamplingPriority = 2
)

func GetSamplingPriority 

func GetSamplingPriority(t *pb.TraceChunk) (SamplingPriority, bool)

GetSamplingPriority returns the value of the sampling priority metric set on this span and a boolean indicating if such a metric was actually found or not.

type ScoreSampler 

type ScoreSampler struct {
	*Sampler
	// contains filtered or unexported fields
}

ScoreSampler samples pieces of traces by computing a signature based on spans (service, name, rsc, http.status, error.type) scoring it and applying a rate. The rates are applied on the TraceID to maximize the number of chunks with errors caught for the same traceID. For a set traceID: P(chunk1 kept and chunk2 kept) = min(P(chunk1 kept), P(chunk2 kept))

func (ScoreSampler) Sample 

func (s ScoreSampler) Sample(trace pb.Trace, root *pb.Span, env string) bool

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

type ServiceSignature 

type ServiceSignature struct{ Name, Env string }

ServiceSignature represents a unique way to identify a service.

func (ServiceSignature) Hash 

func (s ServiceSignature) Hash() Signature

Hash generates the signature of a trace with minimal information such as service and env, this is typically used by distributed sampling based on priority, and used as a key to store the desired rate for a given service,env tuple.

func (ServiceSignature) String 

func (s ServiceSignature) String() string

type Signature 

type Signature uint64

Signature is a hash representation of trace or a service, used to identify simlar signatures.

Source Files

View all Source files

Jump to

Keyboard shortcuts

? : This menu
/ : Search site
f or F : Jump to
y or Y : Canonical URL
go.dev uses cookies from Google to deliver and enhance the quality of its services and to analyze traffic. Learn more.