Add spec for AlwaysRecord sampler

CHANGELOG.md

@@ -13,6 +13,8 @@ release.
 
 - Deprecate Zipkin exporter document and make exporter implementation optional.
   ([#4715](https://github.com/open-telemetry/opentelemetry-specification/pull/4715/))
+- Add spec for `AlwaysRecord` sampler
+  ([#4699](https://github.com/open-telemetry/opentelemetry-specification/pull/4699))
 
 ### Metrics
 

spec-compliance-matrix.md

@@ -90,6 +90,7 @@ formats is required. Implementing more than one format is optional.
 | [Support W3C Trace Context Level 2 randomness](specification/trace/sdk.md#traceid-randomness) | X | - |  |  |  |  |  |  |  |  |  |  |
 | [TraceIdRatioBased sampler implements OpenTelemetry tracestate `th` field](specification/trace/sdk.md#traceidratiobased) | X | - |  |  |  |  |  |  |  |  |  |  |
 | [CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler) | X | - |  |  |  |  |  |  |  |  |  |  |
+| [Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord) |  | - |  |  |  |  |  |  |  |  |  |  |
 
 ## Baggage
 

spec-compliance-matrix/cpp.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/dotnet.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/erlang.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/go.yaml

@@ -157,6 +157,8 @@ sections:
             status: '-'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '-'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '-'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/java.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/js.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/php.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/python.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/ruby.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/rust.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/swift.yaml

@@ -157,6 +157,8 @@ sections:
             status: '?'
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             status: '?'
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
+            status: '?'
   - name: Baggage
     features:
       - name: Basic support

spec-compliance-matrix/template.yaml

@@ -117,6 +117,7 @@ sections:
             optional: true
           - name: '[CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler)'
             optional: true
+          - name: '[Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord)'
   - name: Baggage
     features:
       - name: Basic support

specification/trace/sdk.md

@@ -41,6 +41,7 @@ weight: 3
       - [Compatibility warnings for `ProbabilitySampler`](#compatibility-warnings-for-probabilitysampler)
     + [ParentBased](#parentbased)
     + [JaegerRemoteSampler](#jaegerremotesampler)
+    + [AlwaysRecord](#alwaysrecord)
     + [CompositeSampler](#compositesampler)
       - [ComposableSampler](#composablesampler)
         * [GetSamplingIntent](#getsamplingintent)
@@ -603,6 +604,30 @@ The following configuration properties should be available when creating the sam
 [jaeger-remote-sampling-api]: https://www.jaegertracing.io/docs/1.41/architecture/apis/#remote-sampling-configuration-stable
 [jaeger-adaptive-sampling]: https://www.jaegertracing.io/docs/1.41/architecture/sampling/#adaptive-sampling
 
+#### AlwaysRecord
+
+**Status**: [Development](../document-status.md)
+
+`AlwaysRecord` is a sampler decorator that ensures every span is passed to
+the `SpanProcessor`, even those that would normally be dropped. It does this
+by converting `DROP` decisions from the wrapped sampler into `RECORD_ONLY`
+decisions, allowing processors to see all spans without sending them to
+exporters. This is typically used to enable accurate span-to-metrics processing.
+
+Based on the decision from the wrapped root sampler, `AlwaysRecord` MUST behave
+as follows:
+
+| Root sampler decision | AlwaysRecord decision |
+|-----------------------|-----------------------|
+| `DROP`                | `RECORD_ONLY`         |
+| `RECORD_ONLY`         | `RECORD_ONLY`         |
+| `RECORD_AND_SAMPLE`   | `RECORD_AND_SAMPLE`   |
+
+Required parameters:
+
+* `root(Sampler)` - The sampler being wrapped; it provides the original
+sample/drop decision that AlwaysRecord modifies.
+
 #### CompositeSampler
 
 **Status**: [Development](../document-status.md)