Connect cardinality limit to metric SDK

sdk/metric/limit.go

@@ -0,0 +1,28 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metric // import "go.opentelemetry.io/otel/sdk/metric"
+
+import "go.opentelemetry.io/otel/sdk/metric/internal/x"
+
+func cardinalityLimit() int {
+	if !x.Enabled(x.CardinalityLimit) {
+		return 0
+	}
+
+	// TODO: make this configurable.
+
+	// Default 2000.
+	return 2000
+}

sdk/metric/pipeline.go

@@ -349,7 +349,8 @@ func (i *inserter[N]) cachedAggregator(scope instrumentation.Scope, kind Instrum
 	normID := id.normalize()
 	cv := i.aggregators.Lookup(normID, func() aggVal[N] {
 		b := aggregate.Builder[N]{
-			Temporality: i.pipeline.reader.temporality(kind),
+			Temporality:      i.pipeline.reader.temporality(kind),
+			AggregationLimit: cardinalityLimit(),
 		}
 		if len(stream.AllowAttributeKeys) > 0 {
 			b.Filter = stream.attributeFilter()