# Adaptive Tail Sampling Processor

<!-- llms-txt-link: /llms.txt -->

> OpenTelemetry Collector processor · contrib distribution

The Adaptive Tail Sampling Processor performs adaptive trace sampling using first-match rules-based routing to adaptive samplers. Each sampler produces a known sample rate which is encoded as `ot=th` in W3C TraceState for correct downstream metric weighting.

- **Component ID**: `contrib-adaptivetailsamplingprocessor`
- **Name**: `adaptivetailsamplingprocessor`
- **Type**: processor
- **Distribution**: contrib
- **Repository**: `opentelemetry-collector-contrib`

## Stability

| Level | Signals |
| --- | --- |
| development | traces |

## Internal telemetry

| Metric | Type | Value type | Unit | Stability | Enabled | Attributes | Description |
| --- | --- | --- | --- | --- | --- | --- | --- |
| `processor_adaptive_tail_sampling_decision_sample_rate` | histogram | int | {rate} | development | yes |  | Distribution of effective sample rates produced per rule. Useful for detecting adaptive samplers settling at unexpected rates. |
| `processor_adaptive_tail_sampling_decision_triggers` | sum (monotonic) | int | {decisions} | development | yes |  | Number of trace decisions made, labelled by which event triggered the decision (root_span, trace_timeout, eviction, shutdown, span_limit). |
| `processor_adaptive_tail_sampling_fingerprint_duration` | histogram | int | us | development | yes |  | Time spent extracting a rule's fingerprint per decision, in microseconds, labelled by rule. A relative signal for spotting expensive fingerprints (wide scopes such as any. on large traces); absolute values depend on host and load. |
| `processor_adaptive_tail_sampling_incoming_tracestate_unparseable` | sum (monotonic) | int | {spans} | development | yes |  | Number of spans whose incoming W3C tracestate could not be parsed when applying the sampling threshold. |
| `processor_adaptive_tail_sampling_ottl_eval_errors` | sum (monotonic) | int | {errors} | development | yes |  | Number of OTTL condition evaluation errors, labelled by the rule the condition belongs to (_root_span_condition for the root-span condition). |
| `processor_adaptive_tail_sampling_trace_span_count` | histogram | int | {spans} | development | yes |  | Distribution of buffered span counts per trace at decision time, labelled by rule. Useful for sizing span_limit against the real trace-size distribution. |
| `processor_adaptive_tail_sampling_traces_active` | gauge | int | {traces} | development | yes |  | Number of traces currently in the accumulation buffer awaiting a decision. |
| `processor_adaptive_tail_sampling_traces_dropped` | sum (monotonic) | int | {traces} | development | yes |  | Number of traces that were dropped, labelled by the rule that selected them. Sentinel rule values are prefixed with an underscore (e.g. _unmatched, _eviction). |
| `processor_adaptive_tail_sampling_traces_evicted` | sum (monotonic) | int | {traces} | development | yes |  | Number of traces evicted from the buffer due to num_traces pressure. Evicted traces are decided immediately per the configured eviction policy. |
| `processor_adaptive_tail_sampling_traces_sampled` | sum (monotonic) | int | {traces} | development | yes |  | Number of traces that were sampled, labelled by the rule that selected them. Sentinel rule values are prefixed with an underscore (e.g. _eviction). |

## Data

- **JSON**: [/data/collector/components/contrib-adaptivetailsamplingprocessor/contrib-adaptivetailsamplingprocessor-d22d26eeffc4.json](/data/collector/components/contrib-adaptivetailsamplingprocessor/contrib-adaptivetailsamplingprocessor-d22d26eeffc4.json)
- **Explore**: [/collector/components/contrib/adaptivetailsamplingprocessor](/collector/components/contrib/adaptivetailsamplingprocessor)