Clarify a default-enabled behavior for Metric Views (open-telemetry#2417

)
carlosalberto · Mar 22, 2022 · 45af7fd · 45af7fd
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -45,6 +45,10 @@ release.
   Asynchronous Counter, and Histogram instruments choose Delta
   temporality by default.
   ([#2404](https://github.com/open-telemetry/opentelemetry-specification/pull/2404)).
+- Clarify that instruments are enabled by default, even when Views are configured.
+  Require support for the match-all View expression having `name=*` to support
+  disabling instruments by default.
+  ([#2417](https://github.com/open-telemetry/opentelemetry-specification/pull/2417)).
 
 ### Logs
 

diff --git a/spec-compliance-matrix.md b/spec-compliance-matrix.md
@@ -165,6 +165,8 @@ Disclaimer: this list of features is still a work in progress, please refer to t
 | The updated configuration applies to all already returned `Meter`s.                                                                                                          | if above | -  |  -   |    |    -   |      |        |     |      |     |   +  |       |
 | There is a way to register `View`s with a `MeterProvider`.                                                                                                                   |          | -  |  +   |    |    +   |      |        |     |      |     |   +  |       |
 | The `View` instrument selection criteria is as specified.                                                                                                                    |          |    |  +   |    |    -   |      |        |     |      |     |   +  |       |
+| The `View` instrument selection criteria supports wildcards.                                                                                                                 | X        |    |      |    |        |      |        |     |      |     |      |       |
+| The `View` instrument selection criteria supports the match-all wildcard.                                                                                                    |          |    |      |    |        |      |        |     |      |     |      |       |
 | The name of the `View` can be specified.                                                                                                                                     |          |    |  +   |    |    -   |      |        |     |      |     |   +  |       |
 | The `View` allows configuring the name description, attributes keys and aggregation of the resulting metric stream.                                                          |          |    |  ?   |    |    -   |      |        |     |      |     |   -  |       |
 | The `View` allows configuring the exemplar reservoir of resulting metric stream.                                                                                             | X        |    |  ?   |    |    -   |      |        |     |      |     |   -  |       |

diff --git a/specification/metrics/sdk.md b/specification/metrics/sdk.md
@@ -153,7 +153,9 @@ are the inputs:
   * The `name` of the Instrument(s). [OpenTelemetry SDK](../overview.md#sdk)
     authors MAY choose to support wildcard characters, with the question mark
     (`?`) matching exactly one character and the asterisk character (`*`)
-    matching zero or more characters.
+    matching zero or more characters.  If wildcards are not supported in general,
+    OpenTelemetry SDKs MUST specifically recognize the single `*` wildcard
+    as matching all instruments.
   * The `name` of the Meter (optional).
   * The `version` of the Meter (optional).
   * The `schema_url` of the Meter (optional).
@@ -214,11 +216,9 @@ made with an Instrument:
       know (e.g. expose
       [self-diagnostics logs](../error-handling.md#self-diagnostics)).
   * If the Instrument could not match with any of the registered `View`(s), the
-    SDK SHOULD provide a default behavior. The SDK SHOULD also provide a way for
-    the user to turn off the default behavior via MeterProvider (which means the
-    Instrument will be ignored when there is no match). Individual
-    implementations can decide what the default behavior is, and how to turn the
-    default behavior off.
+    SDK SHOULD enable the instrument using the default aggregation and temporality.
+    Users can configure match-all Views using [Drop aggregation](#drop-aggregation)
+    to disable instruments by default.
 
 Here are some examples: