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Published: Feb 9, 2021 License: Apache-2.0 Imports: 16 Imported by: 0



Package view contains support for collecting and exposing aggregates over stats.

In order to collect measurements, views need to be defined and registered. A view allows recorded measurements to be filtered and aggregated.

All recorded measurements can be grouped by a list of tags.

OpenCensus provides several aggregation methods: Count, Distribution and Sum.

Count only counts the number of measurement points recorded. Distribution provides statistical summary of the aggregated data by counting how many recorded measurements fall into each bucket. Sum adds up the measurement values. LastValue just keeps track of the most recently recorded measurement value. All aggregations are cumulative.

Views can be registered and unregistered at any time during program execution.

Libraries can define views but it is recommended that in most cases registering views be left up to applications.


Collected and aggregated data can be exported to a metric collection backend by registering its exporter.

Multiple exporters can be registered to upload the data to various different back ends.



This section is empty.


View Source
var ErrNegativeBucketBounds = errors.New("negative bucket bounds not supported")

ErrNegativeBucketBounds error returned if histogram contains negative bounds.

Deprecated: this should not be public.


func Register

func Register(views ...*View) error

Register begins collecting data for the given views. Once a view is registered, it reports data to the registered exporters.

func RegisterExporter

func RegisterExporter(e Exporter)

RegisterExporter registers an exporter. Collected data will be reported via all the registered exporters. Once you no longer want data to be exported, invoke UnregisterExporter with the previously registered exporter.

Binaries can register exporters, libraries shouldn't register exporters.

func SetReportingPeriod

func SetReportingPeriod(d time.Duration)

SetReportingPeriod sets the interval between reporting aggregated views in the program. If duration is less than or equal to zero, it enables the default behavior.

Note: each exporter makes different promises about what the lowest supported duration is. For example, the Stackdriver exporter recommends a value no lower than 1 minute. Consult each exporter per your needs.

func Unregister

func Unregister(views ...*View)

Unregister the given views. Data will not longer be exported for these views after Unregister returns. It is not necessary to unregister from views you expect to collect for the duration of your program execution.

func UnregisterExporter

func UnregisterExporter(e Exporter)

UnregisterExporter unregisters an exporter.


type AggType

type AggType int

AggType represents the type of aggregation function used on a View.

const (
	AggTypeNone         AggType = iota // no aggregation; reserved for future use.
	AggTypeCount                       // the count aggregation, see Count.
	AggTypeSum                         // the sum aggregation, see Sum.
	AggTypeDistribution                // the distribution aggregation, see Distribution.
	AggTypeLastValue                   // the last value aggregation, see LastValue.

All available aggregation types.

func (AggType) String

func (t AggType) String() string

type Aggregation

type Aggregation struct {
	Type    AggType   // Type is the AggType of this Aggregation.
	Buckets []float64 // Buckets are the bucket endpoints if this Aggregation represents a distribution, see Distribution.
	// contains filtered or unexported fields

Aggregation represents a data aggregation method. Use one of the functions: Count, Sum, or Distribution to construct an Aggregation.

func Count

func Count() *Aggregation

Count indicates that data collected and aggregated with this method will be turned into a count value. For example, total number of accepted requests can be aggregated by using Count.

func Distribution

func Distribution(bounds ...float64) *Aggregation

Distribution indicates that the desired aggregation is a histogram distribution.

A distribution aggregation may contain a histogram of the values in the population. The bucket boundaries for that histogram are described by the bounds. This defines len(bounds)+1 buckets.

If len(bounds) >= 2 then the boundaries for bucket index i are:

[-infinity, bounds[i]) for i = 0
[bounds[i-1], bounds[i]) for 0 < i < length
[bounds[i-1], +infinity) for i = length

If len(bounds) is 0 then there is no histogram associated with the distribution. There will be a single bucket with boundaries (-infinity, +infinity).

If len(bounds) is 1 then there is no finite buckets, and that single element is the common boundary of the overflow and underflow buckets.

func LastValue

func LastValue() *Aggregation

LastValue only reports the last value recorded using this aggregation. All other measurements will be dropped.

func Sum

func Sum() *Aggregation

Sum indicates that data collected and aggregated with this method will be summed up. For example, accumulated request bytes can be aggregated by using Sum.

type AggregationData

type AggregationData interface {
	// contains filtered or unexported methods

AggregationData represents an aggregated value from a collection. They are reported on the view data during exporting. Mosts users won't directly access aggregration data.

type CountData

type CountData struct {
	Value int64

CountData is the aggregated data for the Count aggregation. A count aggregation processes data and counts the recordings.

Most users won't directly access count data.

type Data

type Data struct {
	View       *View
	Start, End time.Time
	Rows       []*Row

A Data is a set of rows about usage of the single measure associated with the given view. Each row is specific to a unique set of tags.

type DistributionData

type DistributionData struct {
	Count           int64   // number of data points aggregated
	Min             float64 // minimum value in the distribution
	Max             float64 // max value in the distribution
	Mean            float64 // mean of the distribution
	SumOfSquaredDev float64 // sum of the squared deviation from the mean
	CountPerBucket  []int64 // number of occurrences per bucket
	// ExemplarsPerBucket is slice the same length as CountPerBucket containing
	// an exemplar for the associated bucket, or nil.
	ExemplarsPerBucket []*metricdata.Exemplar
	// contains filtered or unexported fields

DistributionData is the aggregated data for the Distribution aggregation.

Most users won't directly access distribution data.

For a distribution with N bounds, the associated DistributionData will have N+1 buckets.

func (*DistributionData) Sum

func (a *DistributionData) Sum() float64

Sum returns the sum of all samples collected.

type Exporter

type Exporter interface {
	ExportView(viewData *Data)

Exporter exports the collected records as view data.

The ExportView method should return quickly; if an Exporter takes a significant amount of time to process a Data, that work should be done on another goroutine.

It is safe to assume that ExportView will not be called concurrently from multiple goroutines.

The Data should not be modified.

type LastValueData

type LastValueData struct {
	Value float64

LastValueData returns the last value recorded for LastValue aggregation.

type Row

type Row struct {
	Tags []tag.Tag
	Data AggregationData

Row is the collected value for a specific set of key value pairs a.k.a tags.

func RetrieveData

func RetrieveData(viewName string) ([]*Row, error)

RetrieveData gets a snapshot of the data collected for the the view registered with the given name. It is intended for testing only.

func (*Row) Equal

func (r *Row) Equal(other *Row) bool

Equal returns true if both rows are equal. Tags are expected to be ordered by the key name. Even if both rows have the same tags but the tags appear in different orders it will return false.

func (*Row) String

func (r *Row) String() string

type SumData

type SumData struct {
	Value float64

SumData is the aggregated data for the Sum aggregation. A sum aggregation processes data and sums up the recordings.

Most users won't directly access sum data.

type View

type View struct {
	Name        string // Name of View. Must be unique. If unset, will default to the name of the Measure.
	Description string // Description is a human-readable description for this view.

	// TagKeys are the tag keys describing the grouping of this view.
	// A single Row will be produced for each combination of associated tag values.
	TagKeys []tag.Key

	// Measure is a stats.Measure to aggregate in this view.
	Measure stats.Measure

	// Aggregation is the aggregation function to apply to the set of Measurements.
	Aggregation *Aggregation

View allows users to aggregate the recorded stats.Measurements. Views need to be passed to the Register function before data will be collected and sent to Exporters.

func Find

func Find(name string) (v *View)

Find returns a registered view associated with this name. If no registered view is found, nil is returned.

func (*View) WithName

func (v *View) WithName(name string) *View

WithName returns a copy of the View with a new name. This is useful for renaming views to cope with limitations placed on metric names by various backends.

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