sdk/metric: Apply Cardinality Limits to Aggregations (#7081)

Fixes https://github.com/open-telemetry/opentelemetry-go/issues/6977
Towards https://github.com/open-telemetry/opentelemetry-go/issues/6887

## What

- Cardinality limits are enforced during aggregation.
- Exceeding the limit results in dropping excess data or other specified
behavior.
- Performance benchmarks confirm no significant degradation due to the
limit enforcement.

## Notes
Tests will be added in a separate PR, as mentioned in
https://github.com/open-telemetry/opentelemetry-go/issues/6978

---------

Co-authored-by: Damien Mathieu <42@dmathieu.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -41,7 +41,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   - `RPCGRPCResponseMetadata`
 - Add `ErrorType` attribute helper function to the `go.opentelmetry.io/otel/semconv/v1.34.0` package. (#6962)
 - Add `WithAllowKeyDuplication` in `go.opentelemetry.io/otel/sdk/log` which can be used to disable deduplication for log records. (#6968)
-- Add `WithCardinalityLimit` option to configure the cardinality limit in `go.opentelemetry.io/otel/sdk/metric`. (#6996, #7065)
+- Add `WithCardinalityLimit` option to configure the cardinality limit in `go.opentelemetry.io/otel/sdk/metric`. (#6996, #7065, #7081)
 - Add `Clone` method to `Record` in `go.opentelemetry.io/otel/log` that returns a copy of the record with no shared state. (#7001)
 - The `go.opentelemetry.io/otel/semconv/v1.36.0` package.
   The package contains semantic conventions from the `v1.36.0` version of the OpenTelemetry Semantic Conventions.

sdk/metric/pipeline.go

@@ -17,7 +17,6 @@ import (
 	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/internal"
 	"go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
-	"go.opentelemetry.io/otel/sdk/metric/internal/x"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
@@ -37,17 +36,24 @@ type instrumentSync struct {
 	compAgg     aggregate.ComputeAggregation
 }
 
-func newPipeline(res *resource.Resource, reader Reader, views []View, exemplarFilter exemplar.Filter) *pipeline {
+func newPipeline(
+	res *resource.Resource,
+	reader Reader,
+	views []View,
+	exemplarFilter exemplar.Filter,
+	cardinalityLimit int,
+) *pipeline {
 	if res == nil {
 		res = resource.Empty()
 	}
 	return &pipeline{
-		resource:        res,
+		resource:         res,
-		reader:          reader,
+		reader:           reader,
-		views:           views,
+		views:            views,
-		int64Measures:   map[observableID[int64]][]aggregate.Measure[int64]{},
+		int64Measures:    map[observableID[int64]][]aggregate.Measure[int64]{},
-		float64Measures: map[observableID[float64]][]aggregate.Measure[float64]{},
+		float64Measures:  map[observableID[float64]][]aggregate.Measure[float64]{},
-		exemplarFilter:  exemplarFilter,
+		exemplarFilter:   exemplarFilter,
+		cardinalityLimit: cardinalityLimit,
 		// aggregations is lazy allocated when needed.
 	}
 }
@@ -65,12 +71,13 @@ type pipeline struct {
 	views  []View
 
 	sync.Mutex
-	int64Measures   map[observableID[int64]][]aggregate.Measure[int64]
+	int64Measures    map[observableID[int64]][]aggregate.Measure[int64]
-	float64Measures map[observableID[float64]][]aggregate.Measure[float64]
+	float64Measures  map[observableID[float64]][]aggregate.Measure[float64]
-	aggregations    map[instrumentation.Scope][]instrumentSync
+	aggregations     map[instrumentation.Scope][]instrumentSync
-	callbacks       []func(context.Context) error
+	callbacks        []func(context.Context) error
-	multiCallbacks  list.List
+	multiCallbacks   list.List
-	exemplarFilter  exemplar.Filter
+	exemplarFilter   exemplar.Filter
+	cardinalityLimit int
 }
 
 // addInt64Measure adds a new int64 measure to the pipeline for each observer.
@@ -388,10 +395,9 @@ func (i *inserter[N]) cachedAggregator(
 		b.Filter = stream.AttributeFilter
 		// A value less than or equal to zero will disable the aggregation
 		// limits for the builder (an all the created aggregates).
-		// CardinalityLimit.Lookup returns 0 by default if unset (or
+		// cardinalityLimit will be 0 by default if unset (or
 		// unrecognized input). Use that value directly.
-		b.AggregationLimit, _ = x.CardinalityLimit.Lookup()
+		b.AggregationLimit = i.pipeline.cardinalityLimit
-
 		in, out, err := i.aggregateFunc(b, stream.Aggregation, kind)
 		if err != nil {
 			return aggVal[N]{0, nil, err}
@@ -590,10 +596,16 @@ func isAggregatorCompatible(kind InstrumentKind, agg Aggregation) error {
 // measurement.
 type pipelines []*pipeline
 
-func newPipelines(res *resource.Resource, readers []Reader, views []View, exemplarFilter exemplar.Filter) pipelines {
+func newPipelines(
+	res *resource.Resource,
+	readers []Reader,
+	views []View,
+	exemplarFilter exemplar.Filter,
+	cardinalityLimit int,
+) pipelines {
 	pipes := make([]*pipeline, 0, len(readers))
 	for _, r := range readers {
-		p := newPipeline(res, r, views, exemplarFilter)
+		p := newPipeline(res, r, views, exemplarFilter, cardinalityLimit)
 		r.register(p)
 		pipes = append(pipes, p)
 	}

sdk/metric/pipeline_registry_test.go

@@ -392,7 +392,7 @@ func testCreateAggregators[N int64 | float64](t *testing.T) {
 	for _, tt := range testcases {
 		t.Run(tt.name, func(t *testing.T) {
 			var c cache[string, instID]
-			p := newPipeline(nil, tt.reader, tt.views, exemplar.AlwaysOffFilter)
+			p := newPipeline(nil, tt.reader, tt.views, exemplar.AlwaysOffFilter, 0)
 			i := newInserter[N](p, &c)
 			readerAggregation := i.readerDefaultAggregation(tt.inst.Kind)
 			input, err := i.Instrument(tt.inst, readerAggregation)
@@ -414,7 +414,7 @@ func TestCreateAggregators(t *testing.T) {
 
 func testInvalidInstrumentShouldPanic[N int64 | float64]() {
 	var c cache[string, instID]
-	i := newInserter[N](newPipeline(nil, NewManualReader(), []View{defaultView}, exemplar.AlwaysOffFilter), &c)
+	i := newInserter[N](newPipeline(nil, NewManualReader(), []View{defaultView}, exemplar.AlwaysOffFilter, 0), &c)
 	inst := Instrument{
 		Name: "foo",
 		Kind: InstrumentKind(255),
@@ -430,7 +430,7 @@ func TestInvalidInstrumentShouldPanic(t *testing.T) {
 
 func TestPipelinesAggregatorForEachReader(t *testing.T) {
 	r0, r1 := NewManualReader(), NewManualReader()
-	pipes := newPipelines(resource.Empty(), []Reader{r0, r1}, nil, exemplar.AlwaysOffFilter)
+	pipes := newPipelines(resource.Empty(), []Reader{r0, r1}, nil, exemplar.AlwaysOffFilter, 0)
 	require.Len(t, pipes, 2, "created pipelines")
 
 	inst := Instrument{Name: "foo", Kind: InstrumentKindCounter}
@@ -504,7 +504,7 @@ func TestPipelineRegistryCreateAggregators(t *testing.T) {
 
 	for _, tt := range testCases {
 		t.Run(tt.name, func(t *testing.T) {
-			p := newPipelines(resource.Empty(), tt.readers, tt.views, exemplar.AlwaysOffFilter)
+			p := newPipelines(resource.Empty(), tt.readers, tt.views, exemplar.AlwaysOffFilter, 0)
 			testPipelineRegistryResolveIntAggregators(t, p, tt.wantCount)
 			testPipelineRegistryResolveFloatAggregators(t, p, tt.wantCount)
 			testPipelineRegistryResolveIntHistogramAggregators(t, p, tt.wantCount)
@@ -558,7 +558,7 @@ func TestPipelineRegistryResource(t *testing.T) {
 	readers := []Reader{NewManualReader()}
 	views := []View{defaultView, v}
 	res := resource.NewSchemaless(attribute.String("key", "val"))
-	pipes := newPipelines(res, readers, views, exemplar.AlwaysOffFilter)
+	pipes := newPipelines(res, readers, views, exemplar.AlwaysOffFilter, 0)
 	for _, p := range pipes {
 		assert.True(t, res.Equal(p.resource), "resource not set")
 	}
@@ -571,7 +571,7 @@ func TestPipelineRegistryCreateAggregatorsIncompatibleInstrument(t *testing.T) {
 
 	readers := []Reader{testRdrHistogram}
 	views := []View{defaultView}
-	p := newPipelines(resource.Empty(), readers, views, exemplar.AlwaysOffFilter)
+	p := newPipelines(resource.Empty(), readers, views, exemplar.AlwaysOffFilter, 0)
 	inst := Instrument{Name: "foo", Kind: InstrumentKindObservableGauge}
 
 	var vc cache[string, instID]
@@ -631,7 +631,7 @@ func TestResolveAggregatorsDuplicateErrors(t *testing.T) {
 	fooInst := Instrument{Name: "foo", Kind: InstrumentKindCounter}
 	barInst := Instrument{Name: "bar", Kind: InstrumentKindCounter}
 
-	p := newPipelines(resource.Empty(), readers, views, exemplar.AlwaysOffFilter)
+	p := newPipelines(resource.Empty(), readers, views, exemplar.AlwaysOffFilter, 0)
 
 	var vc cache[string, instID]
 	ri := newResolver[int64](p, &vc)

sdk/metric/pipeline_test.go

@@ -42,7 +42,7 @@ func testSumAggregateOutput(dest *metricdata.Aggregation) int {
 }
 
 func TestNewPipeline(t *testing.T) {
-	pipe := newPipeline(nil, nil, nil, exemplar.AlwaysOffFilter)
+	pipe := newPipeline(nil, nil, nil, exemplar.AlwaysOffFilter, 0)
 
 	output := metricdata.ResourceMetrics{}
 	err := pipe.produce(context.Background(), &output)
@@ -68,7 +68,7 @@ func TestNewPipeline(t *testing.T) {
 
 func TestPipelineUsesResource(t *testing.T) {
 	res := resource.NewWithAttributes("noSchema", attribute.String("test", "resource"))
-	pipe := newPipeline(res, nil, nil, exemplar.AlwaysOffFilter)
+	pipe := newPipeline(res, nil, nil, exemplar.AlwaysOffFilter, 0)
 
 	output := metricdata.ResourceMetrics{}
 	err := pipe.produce(context.Background(), &output)
@@ -77,7 +77,7 @@ func TestPipelineUsesResource(t *testing.T) {
 }
 
 func TestPipelineConcurrentSafe(t *testing.T) {
-	pipe := newPipeline(nil, nil, nil, exemplar.AlwaysOffFilter)
+	pipe := newPipeline(nil, nil, nil, exemplar.AlwaysOffFilter, 0)
 	ctx := context.Background()
 	var output metricdata.ResourceMetrics
 
@@ -142,13 +142,13 @@ func testDefaultViewImplicit[N int64 | float64]() func(t *testing.T) {
 		}{
 			{
 				name: "NoView",
-				pipe: newPipeline(nil, reader, nil, exemplar.AlwaysOffFilter),
+				pipe: newPipeline(nil, reader, nil, exemplar.AlwaysOffFilter, 0),
 			},
 			{
 				name: "NoMatchingView",
 				pipe: newPipeline(nil, reader, []View{
 					NewView(Instrument{Name: "foo"}, Stream{Name: "bar"}),
-				}, exemplar.AlwaysOffFilter),
+				}, exemplar.AlwaysOffFilter, 0),
 			},
 		}
 
@@ -233,7 +233,7 @@ func TestLogConflictName(t *testing.T) {
 			return instID{Name: tc.existing}
 		})
 
-		i := newInserter[int64](newPipeline(nil, nil, nil, exemplar.AlwaysOffFilter), &vc)
+		i := newInserter[int64](newPipeline(nil, nil, nil, exemplar.AlwaysOffFilter, 0), &vc)
 		i.logConflict(instID{Name: tc.name})
 
 		if tc.conflict {
@@ -275,7 +275,7 @@ func TestLogConflictSuggestView(t *testing.T) {
 	var vc cache[string, instID]
 	name := strings.ToLower(orig.Name)
 	_ = vc.Lookup(name, func() instID { return orig })
-	i := newInserter[int64](newPipeline(nil, nil, nil, exemplar.AlwaysOffFilter), &vc)
+	i := newInserter[int64](newPipeline(nil, nil, nil, exemplar.AlwaysOffFilter, 0), &vc)
 
 	viewSuggestion := func(inst instID, stream string) string {
 		return `"NewView(Instrument{` +
@@ -380,7 +380,7 @@ func TestInserterCachedAggregatorNameConflict(t *testing.T) {
 	}
 
 	var vc cache[string, instID]
-	pipe := newPipeline(nil, NewManualReader(), nil, exemplar.AlwaysOffFilter)
+	pipe := newPipeline(nil, NewManualReader(), nil, exemplar.AlwaysOffFilter, 0)
 	i := newInserter[int64](pipe, &vc)
 
 	readerAggregation := i.readerDefaultAggregation(kind)
@@ -621,7 +621,7 @@ func TestPipelineWithMultipleReaders(t *testing.T) {
 func TestPipelineProduceErrors(t *testing.T) {
 	// Create a test pipeline with aggregations
 	pipeReader := NewManualReader()
-	pipe := newPipeline(nil, pipeReader, nil, exemplar.AlwaysOffFilter)
+	pipe := newPipeline(nil, pipeReader, nil, exemplar.AlwaysOffFilter, 0)
 
 	// Set up an observable with callbacks
 	var testObsID observableID[int64]

sdk/metric/provider.go

@@ -42,7 +42,7 @@ func NewMeterProvider(options ...Option) *MeterProvider {
 	flush, sdown := conf.readerSignals()
 
 	mp := &MeterProvider{
-		pipes:      newPipelines(conf.res, conf.readers, conf.views, conf.exemplarFilter),
+		pipes:      newPipelines(conf.res, conf.readers, conf.views, conf.exemplarFilter, conf.cardinalityLimit),
 		forceFlush: flush,
 		shutdown:   sdown,
 	}