Specify preferred Aggregtion and Aggregation Temporality on a per-instrument basis

CHANGELOG.md

@@ -31,6 +31,9 @@ release.
 - Clarify that the periodic metric reader is the default metric reader to be
   paired with push metric exporters (OTLP, stdout, in-memory)
   ([#2379](https://github.com/open-telemetry/opentelemetry-specification/pull/2379)).
+- Specify that preferred Aggregation and Aggregation Temporality are provided on the
+  basis of instrument kind by the Exporter for the Reader's information.
+  ([#2407](https://github.com/open-telemetry/opentelemetry-specification/pull/2407))
 
 ### Logs
 

specification/metrics/sdk.md

@@ -672,25 +672,9 @@ The SDK SHOULD provide a way to allow `MetricReader` to respond to
 idiomatic approach, for example, as `OnForceFlush` and `OnShutdown` callback
 functions.
 
-The SDK SHOULD provide a way to allow the preferred [Aggregation
-Temporality](./datamodel.md#temporality) to be specified for a `MetricReader`
-instance during the setup (e.g. initialization, registration, etc.) time. If the
-preferred temporality is explicitly specified then the SDK SHOULD respect that,
-otherwise use Cumulative.
-
-[OpenTelemetry SDK](../overview.md#sdk)
-authors MAY choose the best idiomatic design for their language:
-
-* Whether to treat the temporality settings as recommendation or enforcement.
-  For example, if the temporality is set to Delta, would the SDK want to perform
-  Cumulative->Delta conversion for an [Asynchronous
-  Counter](./api.md#asynchronous-counter), or downgrade it to a
-  [Gauge](./datamodel.md#gauge), or keep consuming it as Cumulative due to the
-  consideration of [memory
-  efficiency](./supplementary-guidelines.md#memory-management)?
-* Refer to the [supplementary
-  guidelines](./supplementary-guidelines.md#aggregation-temporality), which have
-  more context and suggestions.
+The SDK MUST provide a way to allow the default [Aggregation](#aggregation) and [Aggregation
+Temporality](./datamodel.md#temporality) to be determined on the basis of instrument kind
+for a `MetricReader` instance during setup (e.g. initialization, registration, etc.) time.
 
 ### MetricReader operations
 
@@ -781,8 +765,23 @@ can run at different schedule, for example:
 * Exporter D is a pull exporter which reacts to another scraper over a named
   pipe.
 
-`MetricExporter` SHOULD provide a way to allow `MetricReader` to retrieve its
-preferred temporality.
+`MetricExporter` MUST provide a way to allow `MetricReader` to retrieve its
+default Aggregation and Aggregation Temporality on the basis of instrument kind.
+
+For Exporters not specified in the [supported SDK exporters for
+metrics](./sdk_exporters), [OpenTelemetry Exporter](#metric-exporter)
+authors MAY choose the best design for the corresponding protocol:
+
+* Whether to treat the temporality settings as recommendation or enforcement.
+  For example, if the temporality is set to Delta, would the MetricExporter want to perform
+  Cumulative->Delta conversion for an [Asynchronous
+  Counter](./api.md#asynchronous-counter), or downgrade it to a
+  [Gauge](./datamodel.md#gauge), or keep consuming it as Cumulative due to the
+  consideration of [memory
+  efficiency](./supplementary-guidelines.md#memory-management)?
+* Refer to the [supplementary
+  guidelines](./supplementary-guidelines.md#aggregation-temporality), which have
+  more context and suggestions.
 
 ### Push Metric Exporter
 

specification/metrics/sdk_exporters/in-memory.md

@@ -16,6 +16,9 @@ by default the exporter MUST be paired with a
 In-memory Metrics Exporter MUST support both Cumulative and Delta
 [Temporality](../datamodel.md#temporality).
 
-In-memory Metrics Exporter MUST allow [Aggregation
-Temporality](../datamodel.md#temporality) to be specified, as described in
-[MetricExporter](../sdk.md#metricexporter).
+In-memory Metrics Exporter MUST allow the default [Aggregation
+Temporality](../datamodel.md#temporality) to be specified on the basis of
+instrument kind, as described in [MetricExporter](../sdk.md#metricexporter).
+
+If the default Aggregation Temporality is not specified, In-memory Metrics
+Exporter SHOULD use Cumulative as the default.

specification/metrics/sdk_exporters/otlp.md

@@ -16,21 +16,12 @@ by default the exporter MUST be paired with a
 OTLP Metrics Exporter MUST support both Cumulative and Delta
 [Temporality](../datamodel.md#temporality).
 
-OTLP Metrics Exporter MUST allow [Aggregation
-Temporality](../datamodel.md#temporality) to be specified, as described in
-[MetricExporter](../sdk.md#metricexporter).
+OTLP Metrics Exporter MUST allow the default [Aggregation
+Temporality](../datamodel.md#temporality) to be specified on the basis of
+instrument kind, as described in [MetricExporter](../sdk.md#metricexporter).
 
-If the temporality is not specified, OTLP Metrics Exporter SHOULD use Cumulative
-as the default temporality.
+If the default Aggregation Temporality is not specified, OTLP Metrics
+Exporter SHOULD use Cumulative as the default.
 
 The exporter MUST provide configuration according to the [OpenTelemetry Protocol
 Exporter](../../protocol/exporter.md) specification.
-
-In addition, the exporter MUST provide the following configuration (note: this
-section will be merged to the [OpenTelemetry Protocol
-Exporter](../../protocol/exporter.md) specification once it reaches
-[Stable](../../document-status.md)):
-
-| Description | Default | Env variable |
-| ----------- | ------- | ------------ |
-| The preferred output [Aggregation Temporality](../datamodel.md#temporality), either `CUMULATIVE` or `DELTA` (case insensitive) | `CUMULATIVE` | `OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY`

specification/metrics/sdk_exporters/stdout.md

@@ -20,6 +20,9 @@ StreamExporter, etc.
 "Standard output" Metrics Exporter MUST support both Cumulative and Delta
 [Temporality](../datamodel.md#temporality).
 
-"Standard output" Metrics Exporter MUST allow [Aggregation
-Temporality](../datamodel.md#temporality) to be specified, as described in
-[MetricExporter](../sdk.md#metricexporter).
+"Standard output" Metrics Exporter MUST allow the default [Aggregation
+Temporality](../datamodel.md#temporality) to be specified on the basis of
+instrument kind, as described in [MetricExporter](../sdk.md#metricexporter).
+
+If the default Aggregation Temporality is not specified, "Standard output" Metrics
+Exporter SHOULD use Cumulative as the default.