Recommend a default size of 1 for the `SimpleFixedSizeExemplarReservo…

…ir` (open-telemetry#3670)
mateuszrzeszutek · Aug 25, 2023 · 8e215bd · 8e215bd
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -23,6 +23,8 @@ release.
   ([#3600](https://github.com/open-telemetry/opentelemetry-specification/pull/3600))
 - Clarify that advice is non-identifying.
   ([#3661](https://github.com/open-telemetry/opentelemetry-specification/pull/3661))
+- Define the default size of the `SimpleFixedSizeExemplarReservoir` to be `1`.
+  ([#3670](https://github.com/open-telemetry/opentelemetry-specification/pull/3670))
 
 ### Logs
 

diff --git a/spec-compliance-matrix.md b/spec-compliance-matrix.md
@@ -122,8 +122,8 @@ formats is required. Implementing more than one format is optional.
 | Instrument names conform to the specified syntax.                                                                                                                      |          | -  | +    |     | +      |      |        |     | +   | +   | +    |       |
 | Instrument units conform to the specified syntax.                                                                                                                      |          | -  | +    |     | +      |      |        |     | +    | +   | +    |       |
 | Instrument descriptions conform to the specified syntax.                                                                                                               |          | -  | +    |     | -      |      |        |     |      | -   | +    |       |
-| Instrument advice supports ExplicitBucketBoundaries.                                                                                                                   |          |    |      |     |        |      |        |     |      |     |      |       |
-| Instrument advice supports Attributes.                                                                                                                                 |          |    |      |     |        |      |        |     |      |     |      |       |
+| Instrument advice supports ExplicitBucketBoundaries.                                                                                                                   |          |    | +    |     |        |      |        |     |      |     |      |       |
+| Instrument advice supports Attributes.                                                                                                                                 |          |    | +    |     |        |      |        |     |      |     |      |       |
 | `create_counter` returns a `Counter`.                                                                                                                                  |          | +  | +    | +   | +      |      |        | +   |  +   | +   | +    |       |
 | The API for `Counter` accepts the name, unit and description of the instrument.                                                                                        |          | +  | +    | +   | +      |      |        | +   |  +   | +   | +    |       |
 | `Counter` has an `add` method.                                                                                                                                         |          | +  | +    | +   | +      |      |        | +   |  +   | +   | +    |       |
@@ -208,6 +208,7 @@ formats is required. Implementing more than one format is optional.
 | The metrics SDK provides an `ExemplarReservoir` interface or extension point.                                                                                          | X        |    | -    |     | -      |      |        | +   |      |     | -    |       |
 | An `ExemplarReservoir` has an `offer` method with access to the measurement value, attributes, `Context` and timestamp.                                                | X        |    | -    |     | -      |      |        | +   |      |     | -    |       |
 | The metrics SDK provides a `SimpleFixedSizeExemplarReservoir` that is used by default for all aggregations except `ExplicitBucketHistogram`.                           |          |    | +    |     | -      |      |        | +   |      |     | -    |       |
+| The default size of the `SimpleFixedSizeExemplarReservoir` is `1`.                                                                                                     |          |    |      |     |        |      |        |     |      |     |      |       |
 | The metrics SDK provides an `AlignedHistogramBucketExemplarReservoir` that is used by default for `ExplicitBucketHistogram` aggregation.                               |          |    | +    |     | -      |      |        |     |      |     | -    |       |
 | The metrics SDK provides an `ExemplarFilter` interface or extension point.                                                                                             | X        |    | -    |     | -      |      |        | +   |      |     | -    |       |
 | An `ExemplarFilter` has access to the measurement value, attributes, `Context` and timestamp.                                                                          | X        |    | -    |     | -      |      |        | +   |      |     | -    |       |

diff --git a/specification/metrics/sdk.md b/specification/metrics/sdk.md
@@ -1033,7 +1033,8 @@ cycle. For the above example, that would mean that the `num_measurements_seen`
 count is reset every time the reservoir is collected.
 
 This Exemplar reservoir MAY take a configuration parameter for the size of the
-reservoir pool.
+reservoir pool. If no size configuration is provided, the default size of `1`
+SHOULD be used.
 
 #### AlignedHistogramBucketExemplarReservoir