Multiple mechanisms are responsible for choosing if spans generated by your applications are sent to Datadog (ingested). The logic behind these mechanisms lie in the tracing libraries and in the Datadog Agent. Depending on the configuration, all or some the traffic generated by instrumented services is ingested.

To each span ingested, there is attached a unique ingestion reason referring to one of the mechanisms described in this page. Usage metrics datadog.estimated_usage.apm.ingested_bytes and datadog.estimated_usage.apm.ingested_spans are tagged by ingestion_reason.

Use the Ingestion Reasons dashboard to investigate in context each of these ingestion reasons. Get an overview of the volume attributed to each mechanism, to quickly know which configuration options to focus on.

Head-based sampling

The default sampling mechanism is called head-based sampling. The decision of whether to keep or drop a trace is made at the very beginning of the trace, at the start of the root span. This decision is then propagated to other services as part of their request context, for example as an HTTP request header.

Because the decision is made at the beginning of the trace and then conveyed to all parts of the trace, the trace is guaranteed to be kept or dropped as a whole.

You can set sampling rates for head-based sampling in two places:

• At the Agent level (default)
• At the Tracing Library level: any tracing library mechanism overrides the Agent setup.

In the Agent

ingestion_reason: auto

The Datadog Agent continuously sends sampling rates to tracing libraries to apply at the root of traces. The Agent adjusts rates to achieve a target of overall ten traces per second, distributed to services depending on the traffic.

For instance, if service A has more traffic than service B, the Agent might vary the sampling rate for A such that A keeps no more than seven traces per second, and similarly adjust the sampling rate for B such that B keeps no more than three traces per second, for a total of 10 traces per second.

Remote configuration

Sampling rate configuration in the Agent is configurable remotely if you are using Agent version 7.42.0 or higher. Read How Remote Configuration Works for information about enabling remote configuration in your Agents. With remote configuration, you can change the parameter without having to restart the Agent.

Local configuration

Set Agent’s target traces-per-second in its main configuration file (datadog.yaml) or as an environment variable :

@param max_traces_per_second - integer - optional - default: 10
@env DD_APM_MAX_TPS - integer - optional - default: 10

Notes:

• Remotely configured parameters take precedence over local configurations - environment variables and datadog.yaml configuration.
• The traces-per-second sampling rate set in the Agent only applies to Datadog tracing libraries. It has no effect on other tracing libraries such as OpenTelemetry SDKs.

All the spans from a trace sampled using the Datadog Agent automatically computed sampling rates are tagged with the ingestion reason auto. The ingestion_reason tag is also set on usage metrics. Services using the Datadog Agent default mechanism are labeled as Automatic in the Ingestion Control Page Configuration column.

In tracing libraries: user-defined rules

ingestion_reason: rule

For more granular control, use tracing library sampling configuration options:

• Set a specific sampling rate to apply to all root services for the library, overriding the Agent’s default mechanism.
• Set a sampling rate to apply to specific root services.
• Set a rate limit on the number of ingested traces per second. The default rate limit is 100 traces per second per service instance (when using the Agent default mechanism, the rate limiter is ignored).

Sampling controls can be set for only root services.

Note: These rules are also head-based sampling controls. If the traffic for a service is higher than the configured maximum traces per second, then traces are dropped at the root. It does not create incomplete traces.

The configuration can be set by environment variables or directly in the code:

# using system property
java -Ddd.trace.sampling.rules='[{\"service\": \"my-service\", \"sample_rate\":0.2}]' -javaagent:dd-java-agent.jar -jar my-app.jar

# using environment variables
export DD_TRACE_SAMPLING_RULES='[{"service": "my-service", "sample_rate": 0.2}]'

export DD_TRACE_SAMPLE_RATE=0.1
export DD_TRACE_SAMPLING_RULES='[{"service": "my-service", "sample_rate": 0.5}]'

export DD_TRACE_SAMPLE_RATE=0.1
export DD_TRACE_SAMPLING_RULES='[{"service": "my-service", "sample_rate": 0.5}]'

export DD_TRACE_SAMPLE_RATE=0.1
export DD_TRACE_SAMPLING_RULES='[{"service": "my-service", "sample_rate": 0.5}]'

export DD_TRACE_SAMPLE_RATE=0.1
export DD_TRACE_SAMPLING_RULES='[{"resource": `GET api/list_documents`, "sample_rate": 0.01}]'

tracer.init({
    ingestion: {
        sampler: {
            sampleRate: 0.1,
            rules: [
                { sampleRate: 0.5, service: 'my-service' }
            ]
        }
    }
});

export DD_TRACE_SAMPLE_RATE=0.1
export DD_TRACE_SAMPLING_RULES='[{"service": "my-service", "sample_rate": 0.5}]'

export DD_TRACE_SAMPLE_RATE=0.1
export DD_TRACE_SAMPLING_RULES='[{"service": "my-service", "sample_rate": 0.5}]'

export DD_TRACE_SAMPLE_RATE=0.1
export DD_TRACE_SAMPLING_RULES='[{"service": "my-service", "sample_rate": 0.5}]'

Note: All the spans from a trace sampled using a tracing library configuration are tagged with the ingestion reason rule. Services configured with user-defined sampling rules are marked as Configured in the Ingestion Control Page Configuration column.

Error and rare traces

For traces not caught by the head-based sampling, two additional Datadog Agent sampling mechanisms make sure that critical and diverse traces are kept and ingested. These two samplers keep a diverse set of local traces (set of spans from the same host) by catching all combinations of a predetermined set of tags:

• Error traces: Sampling errors is important for providing visibility on potential system failures.
• Rare traces: Sampling rare traces allows you to keep visibility on your system as a whole, by making sure that low-traffic services and resources are still monitored.

Note: Error and rare samplers are ignored for services for which you set library sampling rules.

Error traces

ingestion_reason: error

The error sampler catches pieces of traces that contain error spans that are not caught by head-based sampling. It catches error traces up to a rate of 10 traces per second (per Agent). It ensures comprehensive visibility on errors when the head-based sampling rate is low.

With Agent version 7.33 and forward, you can configure the error sampler in the Agent main configuration file (datadog.yaml) or with environment variables:

@param errors_per_second - integer - optional - default: 10
@env DD_APM_ERROR_TPS - integer - optional - default: 10

Notes:

1. Set the parameter to 0 to disable the error sampler.
2. The error sampler captures local traces with error spans at the Agent level. If the trace is distributed, there is no guarantee that the complete trace is sent to Datadog.
3. By default, spans dropped by tracing library rules or custom logic such as manual.drop are excluded under the error sampler.

Datadog Agent 7.42.0 and higher

The error sampling is remotely configurable if your using the Agent version 7.42.0 or higher. Follow the documentation to enable remote configuration in your Agents. With remote configuration, you are able to enable the collection of rare spans without having to restart the Datadog Agent.

Datadog Agent 6/7.41.0 and higher

To override the default behavior so that spans dropped by the tracing library rules or custom logic such as manual.drop are included by the error sampler, enable the feature with: DD_APM_FEATURES=error_rare_sample_tracer_drop in the Datadog Agent (or the dedicated Trace Agent container within the Datadog Agent pod in Kubernetes).

Datadog Agent 6/7.33 to 6/7.40.x

Error sampling default behavior can’t be changed for these Agent versions. Upgrade the Datadog Agent to Datadog Agent 6/7.41.0 and higher.

Rare traces

ingestion_reason: rare

The rare sampler sends a set of rare spans to Datadog. It catches combinations of env, service, name, resource, error.type, and http.status up to 5 traces per second (per Agent). It ensures visibility on low traffic resources when the head-based sampling rate is low.

Note: The rare sampler captures local traces at the Agent level. If the trace is distributed, there is no way to guarantee that the complete trace will be sent to Datadog.

Datadog Agent 7.42.0 and higher

The rare sampling rate is remotely configurable if your using the Agent version 7.42.0 or higher. Follow the documentation to enable remote configuration in your Agents. With remote configuration, you are able to change the parameter value without having to restart the Datadog Agent.

Datadog Agent 6/7.41.0 and higher

By default, the rare sampler is not enabled.

Note: When enabled, spans dropped by tracing library rules or custom logic such as manual.drop are excluded under this sampler.

To configure the rare sampler, update the apm_config.enable_rare_sampler setting in the Agent main configuration file (datadog.yaml) or with the environment variable DD_APM_ENABLE_RARE_SAMPLER:

@params apm_config.enable_rare_sampler - boolean - optional - default: false
@env DD_APM_ENABLE_RARE_SAMPLER - boolean - optional - default: false

To evaluate spans dropped by tracing library rules or custom logic such as manual.drop, enable the feature with: DD_APM_FEATURES=error_rare_sample_tracer_drop in the Trace Agent.

Datadog Agent 6/7.33 to 6/7.40.x

By default, the rare sampler is enabled.

Note: When enabled, spans dropped by tracing library rules or custom logic such as manual.drop are excluded under this sampler. To include these spans in this logic, upgrade to Datadog Agent 6.41.0/7.41.0 or higher.

To change the default rare sampler settings, update the apm_config.disable_rare_sampler setting in the Agent main configuration file (datadog.yaml) or with the environment variable DD_APM_DISABLE_RARE_SAMPLER:

@params apm_config.disable_rare_sampler - boolean - optional - default: false
@env DD_APM_DISABLE_RARE_SAMPLER - boolean - optional - default: false

Force keep and drop

ingestion_reason: manual

The head-based sampling mechanism can be overridden at the tracing library level. For example, if you need to monitor a critical transaction, you can force the associated trace to be kept. On the other hand, for unnecessary or repetitive information like health checks, you can force the trace to be dropped.

• Set Manual Keep on a span to indicate that it and all child spans should be ingested. The resulting trace might appear incomplete in the UI if the span in question is not the root span of the trace.

• Set Manual Drop on a span to make sure that no child span is ingested. Error and rare samplers will be ignored in the Agent.

import datadog.trace.api.DDTags;
import io.opentracing.Span;
import datadog.trace.api.Trace;
import io.opentracing.util.GlobalTracer;

public class MyClass {
    @Trace
    public static void myMethod() {
        // grab the active span out of the traced method
        Span span = GlobalTracer.get().activeSpan();
        // Always keep the trace
        span.setTag(DDTags.MANUAL_KEEP, true);
        // method impl follows
    }
}

import datadog.trace.api.DDTags;
import io.opentracing.Span;
import datadog.trace.api.Trace;
import io.opentracing.util.GlobalTracer;

public class MyClass {
    @Trace
    public static void myMethod() {
        // grab the active span out of the traced method
        Span span = GlobalTracer.get().activeSpan();
        // Always Drop the trace
        span.setTag(DDTags.MANUAL_DROP, true);
        // method impl follows
    }
}

from ddtrace import tracer
from ddtrace.constants import MANUAL_DROP_KEY, MANUAL_KEEP_KEY

@tracer.wrap()
def handler():
    span = tracer.current_span()
    # Always Keep the Trace
    span.set_tag(MANUAL_KEEP_KEY)
    # method impl follows

from ddtrace import tracer
from ddtrace.constants import MANUAL_DROP_KEY, MANUAL_KEEP_KEY

@tracer.wrap()
def handler():
    span = tracer.current_span()
    # Always Drop the Trace
    span.set_tag(MANUAL_DROP_KEY)
    # method impl follows

Datadog::Tracing.trace(name, options) do |span, trace|
  trace.keep! # Affects the active trace
  # Method implementation follows
end

Datadog::Tracing.trace(name, options) do |span, trace|
  trace.reject! # Affects the active trace
  # Method implementation follows
end

package main

import (
    "log"
    "net/http"
    "gopkg.in/DataDog/dd-trace-go.v1/ddtrace/ext"
    "gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer"
)

func handler(w http.ResponseWriter, r *http.Request) {
    // Create a span for a web request at the /posts URL.
    span := tracer.StartSpan("web.request", tracer.ResourceName("/posts"))
    defer span.Finish()

    // Always keep this trace:
    span.SetTag(ext.ManualKeep, true)
    //method impl follows

}

package main

import (
    "log"
    "net/http"

    "gopkg.in/DataDog/dd-trace-go.v1/ddtrace/ext"
    "gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer"
)

func handler(w http.ResponseWriter, r *http.Request) {
    // Create a span for a web request at the /posts URL.
    span := tracer.StartSpan("web.request", tracer.ResourceName("/posts"))
    defer span.Finish()

    // Always drop this trace:
    span.SetTag(ext.ManualDrop, true)
    //method impl follows
}

const tracer = require('dd-trace')
const tags = require('dd-trace/ext/tags')

const span = tracer.startSpan('web.request')

// Always keep the trace
span.setTag(tags.MANUAL_KEEP)
//method impl follows

const tracer = require('dd-trace')
const tags = require('dd-trace/ext/tags')

const span = tracer.startSpan('web.request')

// Always drop the trace
span.setTag(tags.MANUAL_DROP)
//method impl follows

using Datadog.Trace;

using(var scope = Tracer.Instance.StartActive("my-operation"))
{
    var span = scope.Span;

    // Always keep this trace
    span.SetTag(Datadog.Trace.Tags.ManualKeep, "true");
    //method impl follows
}

using Datadog.Trace;

using(var scope = Tracer.Instance.StartActive("my-operation"))
{
    var span = scope.Span;

    // Always drop this trace
    span.SetTag(Datadog.Trace.Tags.ManualDrop, "true");
    //method impl follows
}

<?php
  $tracer = \DDTrace\GlobalTracer::get();
  $span = $tracer->getActiveSpan();

  if (null !== $span) {
    // Always keep this trace
    $span->setTag(\DDTrace\Tag::MANUAL_KEEP, true);
  }
?>

<?php
  $tracer = \DDTrace\GlobalTracer::get();
  $span = $tracer->getActiveSpan();

  if (null !== $span) {
    // Always drop this trace
    $span->setTag(\DDTrace\Tag::MANUAL_DROP, true);
  }
?>

...
#include <datadog/tags.h>
...

auto tracer = ...
auto span = tracer->StartSpan("operation_name");
// Always keep this trace
span->SetTag(datadog::tags::manual_keep, {});
//method impl follows

...
#include <datadog/tags.h>
...

auto tracer = ...
auto another_span = tracer->StartSpan("operation_name");
// Always drop this trace

another_span->SetTag(datadog::tags::manual_drop, {});
//method impl follows

Manual trace keeping should happen before context propagation. If it is kept after context propagation, the system can’t ensure that the entire trace is kept across services. Manual trace keep is set at tracing client location, so the trace can still be dropped by Agent or server location based on sampling rules.

Single spans

ingestion_reason: single_span

If you need to sample a specific span, but don’t need the full trace to be available, tracing libraries allow you to set a sampling rate to be configured for a single span.

For example, if you are building metrics from spans to monitor specific services, you can configure span sampling rules to ensure that these metrics are based on 100% of the application traffic, without having to ingest 100% of traces for all the requests flowing through the service.

This feature is available for Datadog Agent v7.40.0+.

Note: Single span sampling rules cannot be used to drop spans that are kept by head-based sampling, only to keep additional spans that are dropped by head-based sampling.

@env DD_SPAN_SAMPLING_RULES=[{"service": "my-service", "name": "http.request", "sample_rate":1.0, "max_per_second": 50}]

@env DD_SPAN_SAMPLING_RULES=[{"service": "my-service", "name": "http.request", "sample_rate":1.0, "max_per_second": 50}]

@env DD_SPAN_SAMPLING_RULES=[{"service": "my-service", "name": "http.request", "sample_rate":1.0, "max_per_second": 50}]

@env DD_SPAN_SAMPLING_RULES=[{"service": "my-service", "name": "http.request", "sample_rate":1.0, "max_per_second": 50}]

@env DD_SPAN_SAMPLING_RULES=[{"resource": "POST /api/create_issue", "tags": { "priority":"high" }, "sample_rate":1.0}]

@env DD_SPAN_SAMPLING_RULES=[{"service": "my-service", "name": "http.request", "sample_rate":1.0, "max_per_second": 50}]

@env DD_SPAN_SAMPLING_RULES=[{"service": "my-service", "name": "http.request", "sample_rate":1.0, "max_per_second": 50}]

@env DD_SPAN_SAMPLING_RULES=[{"service": "my-service", "name": "http.request", "sample_rate":1.0, "max_per_second": 50}]

@env DD_SPAN_SAMPLING_RULES='[{"service": "my-service", "name": "http.request", "sample_rate":1.0, "max_per_second": 50}]'

Product ingested spans

RUM Traces

ingestion_reason:rum

A request from a web or mobile application generates a trace when the backend services are instrumented. The APM integration with Real User Monitoring links web and mobile application requests to their corresponding backend traces so you can see your full frontend and backend data through one lens.

Beginning with version 4.30.0 of the RUM browser SDK, you can control ingested volumes and keep a sampling of the backend traces by configuring the traceSampleRate initialization parameter. Set traceSampleRate to a number between 0 and 100. If no traceSampleRate value is set, a default of 100% of the traces coming from the browser requests are sent to Datadog.

Similarly, control the trace sampling rate in other SDKs by using similar parameters:

Synthetic traces

ingestion_reason:synthetics and ingestion_reason:synthetics-browser

HTTP and browser tests generate traces when the backend services are instrumented. The APM integration with Synthetic Testing links your synthetic tests with the corresponding backend traces. Navigate from a test run that failed to the root cause of the issue by looking at the trace generated by that test run.

By default, 100% of synthetic HTTP and browser tests generate backend traces.

Other products

Some additional ingestion reasons are attributed to spans that are generated by specific Datadog products:

Ingestion mechanisms in OpenTelemetry

ingestion_reason:otel

Depending on your setup with the OpenTelemetry SDKs (using the OpenTelemetry Collector or the Datadog Agent), you have multiple ways of controlling ingestion sampling. See Ingestion Sampling with OpenTelemetry for details about the options available for sampling at the OpenTelemetry SDK, OpenTelemetry Collector, and Datadog Agent level in various OpenTelemetry setups.

Further Reading

Additional helpful documentation, links, and articles:

Ingestion ControlsDOCUMENTATION Trace RetentionDOCUMENTATION Usage MetricsDOCUMENTATION