Metric View API Prototype

[beanliu]

View API was discussed in the OTEP which is not merged yet (OTEP#89). Having a prototype may push this forward (optentelemetry-specification#466).

Inspired by the Python View API Prototype but the approach for the Golang SDK is a bit different.

View only works for synchronous instruments since the semantics for asynchronous instruments is undefined at the moment. So observers functionality does not change.

The uniqueness of a view is defined by a tuple of instrument, label keys and its aggregator factory. Note that an Ungroup view is the same with defining an empty pair of label keys.

Summary of changes:

• Move Aggregator, Aggregation and AggregatorSelector interfaces to otel/metric package to avoid concept dependency cycle. (commit)
• Add View type and RegisterView method as part of the Metric API. (commit)
• Support labels with values unset since this may be a valid case for views. (commit)
• View implementation: (commit)
  • If no views are defined for a metric, a default one that's compatible with the previous semantics is registered automatically while taking a measurement.
  • Bound instruments now has a sequence of aggregators if the metric has more than one view. But views registered after the creation of the bound instrument have no effect on the bind object.
  • Views are stored inside the associate instrument object. A measurement would be recorded for each view.

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ beanliu (432efa3, b9c228e, a77c112, 3a662b2, 227f1ae, 8698dee, 28d204a)

[codecov]

Codecov Report

Merging #1473 (a56d2ad) into main (1952d7b) will decrease coverage by 0.2%.
The diff coverage is 87.2%.

@@           Coverage Diff           @@
##            main   #1473     +/-   ##
=======================================
- Coverage   79.2%   79.0%   -0.3%     
=======================================
  Files        127     129      +2     
  Lines       6659    6768    +109     
=======================================
+ Hits        5280    5350     +70     
- Misses      1124    1163     +39     
  Partials     255     255             

Impacted Files	Coverage Δ
exporters/metric/prometheus/prometheus.go	64.8% <ø> (ø)
exporters/otlp/internal/transform/metric.go	80.5% <ø> (ø)
exporters/otlp/otlp.go	90.9% <ø> (ø)
exporters/stdout/metric.go	76.3% <ø> (ø)
internal/global/meter.go	90.3% <ø> (ø)
metric/aggregation/aggregation.go	0.0% <ø> (ø)
metric/metric_sdkapi.go	100.0% <ø> (ø)
metric/viewlabelconfig_string.go	0.0% <0.0%> (ø)
sdk/metric/aggregator/aggregator.go	100.0% <ø> (ø)
sdk/metric/aggregator/aggregatortest/test.go	84.8% <ø> (ø)
... and 26 more

[MrAlias]

Closing as the metric's part of the specification is going through a large refactor currently and we will likely need to reevaluate the entire signal once it stabilizes, including how we want to approach views.

[ProvoK]

Any news on this? Not being able to specify buckets per single metric(s) is a real blocker for a lot of scenarios.

Is there a way to possible help?