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Configure tail-based sampling

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Configure tail-based sampling

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Enable tail-based sampling in the APM integration settings. When enabled, trace events are mapped to sampling policies. Each sampling policy must specify a sample rate, and can optionally specify other conditions. All of the policy conditions must be true for a trace event to match it.

Trace events are matched to policies in the order specified. Each policy list must conclude with a default policy — one that only specifies a sample rate. This default policy is used to catch remaining trace events that don’t match a stricter policy. Requiring this default policy ensures that traces are only dropped intentionally. If you enable tail-based sampling and send a transaction that does not match any of the policies, APM Server will reject the transaction with the error no matching policy.

Please note that from version 8.3.1 APM Server implements a default storage limit of 3GB, but, due to how the limit is calculated and enforced the actual disk space may still grow slightly over the limit.

Example configuration

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This example defines three tail-based sampling polices:

- sample_rate: 1 
  service.environment: production
  trace.name: "GET /very_important_route"
- sample_rate: .01 
  service.environment: production
  trace.name: "GET /not_important_route"
- sample_rate: .1

Samples 100% of traces in production with the trace name "GET /very_important_route"

Samples 1% of traces in production with the trace name "GET /not_important_route"

Default policy to sample all remaining traces at 10%, e.g. traces in a different environment, like dev, or traces with any other name

Configuration reference

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Top-level tail-based sampling settings:

Enable Tail-based sampling

(bool) Enable and disable tail-based sampling.

Default: false

Interval

(duration) Synchronization interval for multiple APM Servers. Should be in the order of tens of seconds or low minutes.

Default: 1m

Policies

([]policy) Criteria used to match a root transaction to a sample rate. Order is important; the first policy on the list that an event matches is the winner. Each policy list must conclude with a default policy that only specifies a sample rate. The default policy is used to catch remaining trace events that don’t match a stricter policy.

Required when tail-based sampling is enabled.

Policy settings:

Sample rate

sample_rate

(int) The sample rate to apply to trace events matching this policy. Required in each policy.

The sample rate must be greater than 0 and less than or equal to 1. For example, a sample_rate of 0.01 means that 1% of trace events matching the policy will be sampled. A sample_rate of 1 means that 100% of trace events matching the policy will be sampled.

Trace name

trace.name

(string) The trace name for events to match a policy. A match occurs when the configured trace.name matches the transaction.name of the root transaction of a trace. A root transaction is any transaction without a parent.id.

Trace outcome

trace.outcome

(string) The trace outcome for events to match a policy. A match occurs when the configured trace.outcome matches a trace’s event.outcome field. Trace outcome can be success, failure, or unknown.

Service name

service.name

(string) The service name for events to match a policy.

Service Environment

service.environment

(string) The service environment for events to match a policy.
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