feat: Add and enabled Metric cardinality capping by default #2901

cijothomas · 2025-04-04T17:48:06Z

Re-introduce Metric cardinality capping, but this time, with the ability to configure the limit using Views.
The default is 2000, following OTel spec.
There is no ability to change the limit globally (at reader level) - this is not a MUST from the spec, and based on my experience, this is rarely used/needed.
Existing tests are re-enabled, and also enhanced to test customization ability and to test that limits are per cycle.

TODO (in next PR): is to add coverage for all instruments, as only Counters are currently covered.
TODO : doc additions. Depending on the next PR where I plan to introduce customization ability via Advisory, we can decide how best to document this.
TODO(next PR): Fix #2878 too

I expect to send another PR which will enhance the Instrument Advisory parameters to accept cardinality limits via that option. This is not a thing from the spec (but spec does not prohibit offering additional capabilities either), but planned to be added to Rust as using Views is generally non-trivial and my own experience tells it is somewhat confusing.
(Also planning to make a spec enhancement proposal in parallel, but I don't think it is a blocker)

codecov · 2025-04-04T17:52:03Z

Codecov Report

Attention: Patch coverage is 97.16599% with 7 lines in your changes missing coverage. Please review.

Project coverage is 81.3%. Comparing base (86e842c) to head (a190bd1).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-sdk/src/metrics/mod.rs	95.0%	6 Missing ⚠️
opentelemetry-sdk/src/metrics/pipeline.rs	92.8%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2901     +/-   ##
=======================================
+ Coverage   81.0%   81.3%   +0.2%     
=======================================
  Files        125     125             
  Lines      23945   24132    +187     
=======================================
+ Hits       19414   19628    +214     
+ Misses      4531    4504     -27

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opentelemetry-sdk/src/metrics/instrument.rs

opentelemetry-sdk/src/metrics/mod.rs

opentelemetry-sdk/src/metrics/pipeline.rs

opentelemetry-sdk/src/metrics/mod.rs

utpilla · 2025-04-04T22:59:19Z

opentelemetry-sdk/src/metrics/pipeline.rs

            let AggregateFns { measure, collect } = match aggregate_fn(b, &agg, kind) {
                Ok(Some(inst)) => inst,
                other => return other.map(|fs| fs.map(|inst| inst.measure)), // Drop aggregator or error
            };

+            otel_debug!(
+                name : "Metrics.InstrumentCreated",
+                instrument_name = stream.name.as_ref(),


nit: Add Aggregation information as well to understand what kind of instrument was created.

feat: Add and enabled Metric cardinality capping by default

b9d0a50

cijothomas requested a review from a team as a code owner April 4, 2025 17:48

cijothomas commented Apr 4, 2025

View reviewed changes

opentelemetry-sdk/src/metrics/instrument.rs Show resolved Hide resolved