Add SDK span telemetry metrics (#1631)

Co-authored-by: Alexander Wert <AlexanderWert@users.noreply.github.com>
Co-authored-by: Joao Grassi <5938087+joaopgrassi@users.noreply.github.com>

Author: 3 people

.chloggen/sdk-span-metrics.yaml

@@ -0,0 +1,22 @@
+# Use this changelog template to create an entry for release notes.
+#
+# If your change doesn't affect end users you should instead start
+# your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: 'enhancement'
+
+# The name of the area of concern in the attributes-registry, (e.g. http, cloud, db)
+component: 'otel'
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Adds SDK self-monitoring metrics for span processing
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+# The values here must be integers.
+issues: [1631]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

docs/attributes-registry/otel.md

@@ -4,6 +4,7 @@
 # OTel
 
 - [OTel Attributes](#otel-attributes)
+- [OTel Component Attributes](#otel-component-attributes)
 - [OTel Scope Attributes](#otel-scope-attributes)
 - [Deprecated OTel Library Attributes](#deprecated-otel-library-attributes)
 
@@ -13,18 +14,67 @@ Attributes reserved for OpenTelemetry
 
 | Attribute | Type | Description | Examples | Stability |
 |---|---|---|---|---|
+| <a id="otel-span-sampling-result" href="#otel-span-sampling-result">`otel.span.sampling_result`</a> | string | The result value of the sampler for this span | `DROP`; `RECORD_ONLY`; `RECORD_AND_SAMPLE` | ![Development](https://img.shields.io/badge/-development-blue) |
 | <a id="otel-status-code" href="#otel-status-code">`otel.status_code`</a> | string | Name of the code, either "OK" or "ERROR". MUST NOT be set if the status code is UNSET. | `OK`; `ERROR` | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
 | <a id="otel-status-description" href="#otel-status-description">`otel.status_description`</a> | string | Description of the Status if it has a value, otherwise not set. | `resource not found` | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
 
 ---
 
+`otel.span.sampling_result` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.
+
+| Value  | Description | Stability |
+|---|---|---|
+| `DROP` | The span is not sampled and not recording | ![Development](https://img.shields.io/badge/-development-blue) |
+| `RECORD_AND_SAMPLE` | The span is sampled and recording | ![Development](https://img.shields.io/badge/-development-blue) |
+| `RECORD_ONLY` | The span is not sampled, but recording | ![Development](https://img.shields.io/badge/-development-blue) |
+
+---
+
 `otel.status_code` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.
 
 | Value  | Description | Stability |
 |---|---|---|
 | `ERROR` | The operation contains an error. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
 | `OK` | The operation has been validated by an Application developer or Operator to have completed successfully. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
 
+## OTel Component Attributes
+
+Attributes used for OpenTelemetry component self-monitoring
+
+| Attribute | Type | Description | Examples | Stability |
+|---|---|---|---|---|
+| <a id="otel-component-name" href="#otel-component-name">`otel.component.name`</a> | string | A name uniquely identifying the instance of the OpenTelemetry component within its containing SDK instance. [1] | `otlp_grpc_span_exporter/0`; `custom-name` | ![Development](https://img.shields.io/badge/-development-blue) |
+| <a id="otel-component-type" href="#otel-component-type">`otel.component.type`</a> | string | A name identifying the type of the OpenTelemetry component. [2] | `batching_span_processor`; `com.example.MySpanExporter` | ![Development](https://img.shields.io/badge/-development-blue) |
+
+**[1] `otel.component.name`:** Implementations SHOULD ensure a low cardinality for this attribute, even across application or SDK restarts.
+E.g. implementations MUST NOT use UUIDs as values for this attribute.
+
+Implementations MAY achieve these goals by following a `<otel.component.type>/<instance-counter>` pattern, e.g. `batching_span_processor/0`.
+Hereby `otel.component.type` refers to the corresponding attribute value of the component.
+
+The value of `instance-counter` MAY be automatically assigned by the component and uniqueness within the enclosing SDK instance MUST be guaranteed.
+For example, `<instance-counter>` MAY be implemented by using a monotonically increasing counter (starting with `0`), which is incremented every time an
+instance of the given component type is started.
+
+With this implementation, for example the first Batching Span Processor would have `batching_span_processor/0`
+as `otel.component.name`, the second one `batching_span_processor/1` and so on.
+These values will therefore be reused in the case of an application restart.
+
+**[2] `otel.component.type`:** If none of the standardized values apply, implementations SHOULD use the language-defined name of the type.
+E.g. for Java the fully qualified classname SHOULD be used in this case.
+
+---
+
+`otel.component.type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.
+
+| Value  | Description | Stability |
+|---|---|---|
+| `batching_span_processor` | The builtin SDK Batching Span Processor | ![Development](https://img.shields.io/badge/-development-blue) |
+| `otlp_grpc_span_exporter` | OTLP span exporter over gRPC with protobuf serialization | ![Development](https://img.shields.io/badge/-development-blue) |
+| `otlp_http_json_span_exporter` | OTLP span exporter over HTTP with JSON serialization | ![Development](https://img.shields.io/badge/-development-blue) |
+| `otlp_http_span_exporter` | OTLP span exporter over HTTP with protobuf serialization | ![Development](https://img.shields.io/badge/-development-blue) |
+| `simple_span_processor` | The builtin SDK Simple Span Processor | ![Development](https://img.shields.io/badge/-development-blue) |
+
 ## OTel Scope Attributes
 
 Attributes used by non-OTLP exporters to represent OpenTelemetry Scope's concepts.

docs/general/metrics.md

@@ -34,6 +34,7 @@ The following semantic conventions surrounding metrics are defined:
   * [K8s](/docs/system/k8s-metrics.md): For K8s metrics.
   * [Process](/docs/system/process-metrics.md): For standard process metrics.
   * [Runtime Environment](/docs/runtime/README.md#metrics): For runtime environment metrics.
+* [OTel SDK Telemetry](/docs/otel/sdk-metrics.md): Metrics emitted by the OpenTelemetry SDK components.
 
 Apart from semantic conventions for metrics, [traces](trace.md), [logs](logs.md), and [events](events.md), OpenTelemetry also
 defines the concept of overarching [Resources](https://github.com/open-telemetry/opentelemetry-specification/tree/v1.41.0/specification/resource/sdk.md) with