OpenCensus and OpenTracing have merged into OpenTelemetry!



Trace data is often produced in large volumes, it is not only expensive to collect and store but also expensive to transmit.

In order to strike a balance between observability and expenses, traces are sampled. Sampling is the process by which a decision is made on whether to process/export a span or not.


OpenCensus provides these types of samplers

A sampler’s decision affects Span.TraceOptions’ sampling bit by setting or clearing it if the sampler returns True or False respectively.

There are 2 ways of setting a sampler to use:

Global sampler

The global sampler is a sampler that’s set via the global TraceConfig

package main

import ""

func main() {
    // Having already created your sampler "theSampler"
    trace.ApplyConfig(trace.Config{DefaultSampler: theSampler})
package io.opencensus.tutorials.tracing.sampling;

import io.opencensus.trace.config.TraceConfig;

public class App {
    public static void main(String[] args) {
        // Get the global TraceConfig
        TraceConfig globalTraceConfig = Tracing.getTraceConfig();

        // Now update the global TraceConfig
#include "opencensus/trace/sampler.h"
#include "opencensus/trace/trace_config.h"
#include "opencensus/trace/trace_params.h"

int main(int argc, char** argv) {
    opencensus::trace::ProbabilitySampler theSampler(theProbability);
    const struct opencensus::trace::TraceParams globalConfig = {

Per span sampler aka “Span scoped”

This sampler is set when starting a span, via the constructor

import ""

func doWork() {
    // Having already created your sampler "theSampler" and "ctx"
    ctx, span := trace.StartSpan(ctx, "DoWork", trace.WithSampler(theSampler))
package io.opencensus.tutorials.tracing.sampling;

import io.opencensus.trace.common.Scope;

void doWork() {
    // Having already defined "theSampler" and "tracer"
    try (Scope ss = tracer.spanBuilder("DoWork").setSampler(theSampler).startScopedSpan()){
void doWork() {
    // Having already defined "theSampler"
    opencensus::trace::Span theSpan = \
            opencensus::trace::Span::StartSpan("DoWork", nullptr, {&theSampler});



Resource URL
TraceConfig in specs specs/trace/TraceConfig
Per-Span sampler in specs specs/trace/Sampling
GoDoc: ApplyConfig trace.ApplyConfig
JavaDoc: TraceConfig io.opencensus.trace.config.TraceConfig
C++: TraceConfig opencensus::trace::TraceConfig