Otel.Trace.Sampler (otel v0.4.1)

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Hard-coded ParentBased(root=AlwaysOn) sampler — the spec default per trace/sdk.md L421 and the only sampler this SDK ships.

Decision matrix (trace/sdk.md §ParentBased L584-590 with default delegates L579-582):

ParentDecision
absent (root)record_and_sample
sampled (any)record_and_sample
not sampled (any)drop

The full 5-branch ParentBased decorator is collapsed because every branch resolves to AlwaysOn (sampled) or AlwaysOff (not sampled) — local/remote distinction has no behavioural effect with default delegates.

Public API

FunctionRole
should_sample/6SDK (OTel API MUST) — trace/sdk.md §ShouldSample L342-L406
description/0SDK (OTel API MUST) — trace/sdk.md §GetDescription L408-L417

All functions are safe for concurrent use, satisfying spec trace/sdk.md L1284 — "Sampler — ShouldSample and GetDescription MUST be safe to be called concurrently."

References

  • OTel Trace SDK §Sampler: opentelemetry-specification/specification/trace/sdk.md L329-L460
  • OTel Trace SDK §Built-in samplers: same file L418-L590

Summary

Types

primitive()
primitive_any()
sampling_decision()
sampling_result()

Functions

description()

SDK (OTel API MUST) — GetDescription (trace/sdk.md §GetDescription L408-L417).

should_sample(ctx, trace_id, links, name, kind, attributes)

SDK (OTel API MUST) — ShouldSample (trace/sdk.md §ShouldSample L342-L406).

Types

primitive()

@type primitive() ::
  String.t() | {:bytes, binary()} | boolean() | integer() | float() | nil

primitive_any()

@type primitive_any() ::
  primitive() | [primitive_any()] | %{required(String.t()) => primitive_any()}

sampling_decision()

@type sampling_decision() :: :drop | :record_only | :record_and_sample

sampling_result()

@type sampling_result() ::
  {sampling_decision(), %{required(String.t()) => primitive_any()},
   Otel.Trace.TraceState.t()}

Functions

description()

@spec description() :: String.t()

SDK (OTel API MUST) — GetDescription (trace/sdk.md §GetDescription L408-L417).

Returns the spec-style ParentBased descriptor with all five delegate branches enumerated. ParentBased itself has no MUST format; this format mirrors the description the previous composable implementation produced, so external observers (debug pages, log lines) see no string change.

should_sample(ctx, trace_id, links, name, kind, attributes)

@spec should_sample(
  ctx :: Otel.Ctx.t(),
  trace_id :: Otel.Trace.TraceId.t(),
  links :: [Otel.Trace.Link.t()],
  name :: String.t(),
  kind :: Otel.Trace.SpanKind.t(),
  attributes :: %{required(String.t()) => primitive_any()}
) :: sampling_result()

SDK (OTel API MUST) — ShouldSample (trace/sdk.md §ShouldSample L342-L406).

Returns record_and_sample for root spans and any span whose parent has the sampled bit set; drop for spans whose parent has the bit unset. Tracestate is propagated from the parent unchanged.