Experimental metric reader and view cardinality limits

sdk/all/src/test/java/io/opentelemetry/sdk/OpenTelemetrySdkTest.java

@@ -421,7 +421,7 @@ void stringRepresentation() {
                 + "clock=SystemClock{}, "
                 + "resource=Resource{schemaUrl=null, attributes={service.name=\"otel-test\"}}, "
                 + "metricReaders=[PeriodicMetricReader{exporter=MockMetricExporter{}, intervalNanos=60000000000}], "
-                + "views=[RegisteredView{instrumentSelector=InstrumentSelector{instrumentName=instrument}, view=View{name=new-instrument, aggregation=DefaultAggregation, attributesProcessor=NoopAttributesProcessor{}}}]"
+                + "views=[RegisteredView{instrumentSelector=InstrumentSelector{instrumentName=instrument}, view=View{name=new-instrument, aggregation=DefaultAggregation, attributesProcessor=NoopAttributesProcessor{}, cardinalityLimit=2000}}]"
                 + "}, "
                 + "loggerProvider=SdkLoggerProvider{"
                 + "clock=SystemClock{}, "

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/SdkMeterProvider.java

@@ -16,6 +16,7 @@
 import io.opentelemetry.sdk.metrics.export.MetricReader;
 import io.opentelemetry.sdk.metrics.internal.SdkMeterProviderUtil;
 import io.opentelemetry.sdk.metrics.internal.exemplar.ExemplarFilter;
+import io.opentelemetry.sdk.metrics.internal.export.CardinalityLimitSelector;
 import io.opentelemetry.sdk.metrics.internal.export.MetricProducer;
 import io.opentelemetry.sdk.metrics.internal.export.RegisteredReader;
 import io.opentelemetry.sdk.metrics.internal.state.MeterProviderSharedState;
@@ -26,6 +27,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.IdentityHashMap;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -54,17 +56,19 @@ public static SdkMeterProviderBuilder builder() {
 
   SdkMeterProvider(
       List<RegisteredView> registeredViews,
-      List<MetricReader> metricReaders,
+      IdentityHashMap<MetricReader, CardinalityLimitSelector> metricReaders,
       Clock clock,
       Resource resource,
       ExemplarFilter exemplarFilter) {
     long startEpochNanos = clock.now();
     this.registeredViews = registeredViews;
     this.registeredReaders =
-        metricReaders.stream()
+        metricReaders.entrySet().stream()
             .map(
-                reader ->
-                    RegisteredReader.create(reader, ViewRegistry.create(reader, registeredViews)))
+                entry ->
+                    RegisteredReader.create(
+                        entry.getKey(),
+                        ViewRegistry.create(entry.getKey(), entry.getValue(), registeredViews)))
             .collect(toList());
     this.sharedState =
         MeterProviderSharedState.create(clock, resource, exemplarFilter, startEpochNanos);

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/SdkMeterProviderBuilder.java

@@ -10,9 +10,11 @@
 import io.opentelemetry.sdk.metrics.internal.SdkMeterProviderUtil;
 import io.opentelemetry.sdk.metrics.internal.debug.SourceInfo;
 import io.opentelemetry.sdk.metrics.internal.exemplar.ExemplarFilter;
+import io.opentelemetry.sdk.metrics.internal.export.CardinalityLimitSelector;
 import io.opentelemetry.sdk.metrics.internal.view.RegisteredView;
 import io.opentelemetry.sdk.resources.Resource;
 import java.util.ArrayList;
+import java.util.IdentityHashMap;
 import java.util.List;
 import java.util.Objects;
 
@@ -32,7 +34,8 @@ public final class SdkMeterProviderBuilder {
 
   private Clock clock = Clock.getDefault();
   private Resource resource = Resource.getDefault();
-  private final List<MetricReader> metricReaders = new ArrayList<>();
+  private final IdentityHashMap<MetricReader, CardinalityLimitSelector> metricReaders =
+      new IdentityHashMap<>();
   private final List<RegisteredView> registeredViews = new ArrayList<>();
   private ExemplarFilter exemplarFilter = DEFAULT_EXEMPLAR_FILTER;
 
@@ -96,7 +99,11 @@ public SdkMeterProviderBuilder registerView(InstrumentSelector selector, View vi
     Objects.requireNonNull(view, "view");
     registeredViews.add(
         RegisteredView.create(
-            selector, view, view.getAttributesProcessor(), SourceInfo.fromCurrentStack()));
+            selector,
+            view,
+            view.getAttributesProcessor(),
+            view.getCardinalityLimit(),
+            SourceInfo.fromCurrentStack()));
     return this;
   }
 
@@ -106,7 +113,20 @@ public SdkMeterProviderBuilder registerView(InstrumentSelector selector, View vi
    * <p>Note: custom implementations of {@link MetricReader} are not currently supported.
    */
   public SdkMeterProviderBuilder registerMetricReader(MetricReader reader) {
-    metricReaders.add(reader);
+    metricReaders.put(reader, CardinalityLimitSelector.defaultCardinalityLimitSelector());
+    return this;
+  }
+
+  /**
+   * Registers a {@link MetricReader} with a {@link CardinalityLimitSelector}.
+   *
+   * <p>Note: not currently stable but available for experimental use via {@link
+   * SdkMeterProviderUtil#registerMetricReaderWithCardinalitySelector(SdkMeterProviderBuilder,
+   * MetricReader, CardinalityLimitSelector)}.
+   */
+  SdkMeterProviderBuilder registerMetricReader(
+      MetricReader reader, CardinalityLimitSelector cardinalityLimitSelector) {
+    metricReaders.put(reader, cardinalityLimitSelector);
     return this;
   }
 

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/View.java

@@ -32,8 +32,10 @@ static View create(
       @Nullable String name,
       @Nullable String description,
       Aggregation aggregation,
-      AttributesProcessor attributesProcessor) {
-    return new AutoValue_View(name, description, aggregation, attributesProcessor);
+      AttributesProcessor attributesProcessor,
+      int cardinalityLimit) {
+    return new AutoValue_View(
+        name, description, aggregation, attributesProcessor, cardinalityLimit);
   }
 
   View() {}
@@ -58,6 +60,9 @@ static View create(
   /** Returns the attribute processor used for this view. */
   abstract AttributesProcessor getAttributesProcessor();
 
+  /** Returns the cardinality limit for this view. */
+  abstract int getCardinalityLimit();
+
   @Override
   public final String toString() {
     StringJoiner joiner = new StringJoiner(", ", "View{", "}");
@@ -69,6 +74,7 @@ public final String toString() {
     }
     joiner.add("aggregation=" + getAggregation());
     joiner.add("attributesProcessor=" + getAttributesProcessor());
+    joiner.add("cardinalityLimit=" + getCardinalityLimit());
     return joiner.toString();
   }
 }

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/ViewBuilder.java

@@ -7,6 +7,7 @@
 
 import io.opentelemetry.sdk.metrics.internal.SdkMeterProviderUtil;
 import io.opentelemetry.sdk.metrics.internal.aggregator.AggregatorFactory;
+import io.opentelemetry.sdk.metrics.internal.state.MetricStorage;
 import io.opentelemetry.sdk.metrics.internal.view.AttributesProcessor;
 import java.util.Objects;
 import java.util.function.Predicate;
@@ -23,6 +24,7 @@ public final class ViewBuilder {
   @Nullable private String description;
   private Aggregation aggregation = Aggregation.defaultAggregation();
   private AttributesProcessor processor = AttributesProcessor.noop();
+  private int cardinalityLimit = MetricStorage.DEFAULT_MAX_CARDINALITY;
 
   ViewBuilder() {}
 
@@ -85,8 +87,24 @@ ViewBuilder addAttributesProcessor(AttributesProcessor attributesProcessor) {
     return this;
   }
 
+  /**
+   * Set the cardinality limit.
+   *
+   * <p>Note: not currently stable but cardinality limit can be configured via
+   * SdkMeterProviderUtil#setCardinalityLimit(ViewBuilder, int)}.
+   *
+   * @param cardinalityLimit the maximum number of series for a metric
+   */
+  ViewBuilder setCardinalityLimit(int cardinalityLimit) {
+    if (cardinalityLimit <= 0) {
+      throw new IllegalArgumentException("cardinalityLimit must be > 0");
+    }
+    this.cardinalityLimit = cardinalityLimit;
+    return this;
+  }
+
   /** Returns a {@link View} with the configuration of this builder. */
   public View build() {
-    return View.create(name, description, aggregation, processor);
+    return View.create(name, description, aggregation, processor, cardinalityLimit);
   }
 }

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/SdkMeterProviderUtil.java

@@ -8,7 +8,9 @@
 import io.opentelemetry.sdk.metrics.SdkMeterProvider;
 import io.opentelemetry.sdk.metrics.SdkMeterProviderBuilder;
 import io.opentelemetry.sdk.metrics.ViewBuilder;
+import io.opentelemetry.sdk.metrics.export.MetricReader;
 import io.opentelemetry.sdk.metrics.internal.exemplar.ExemplarFilter;
+import io.opentelemetry.sdk.metrics.internal.export.CardinalityLimitSelector;
 import io.opentelemetry.sdk.metrics.internal.view.AttributesProcessor;
 import io.opentelemetry.sdk.metrics.internal.view.StringPredicates;
 import java.lang.reflect.InvocationTargetException;
@@ -26,7 +28,7 @@ private SdkMeterProviderUtil() {}
   /**
    * Reflectively assign the {@link ExemplarFilter} to the {@link SdkMeterProviderBuilder}.
    *
-   * @param sdkMeterProviderBuilder the
+   * @param sdkMeterProviderBuilder the builder
    */
   public static void setExemplarFilter(
       SdkMeterProviderBuilder sdkMeterProviderBuilder, ExemplarFilter exemplarFilter) {
@@ -42,6 +44,28 @@ public static void setExemplarFilter(
     }
   }
 
+  /**
+   * Reflectively add a {@link MetricReader} with the {@link CardinalityLimitSelector} to the {@link
+   * SdkMeterProviderBuilder}.
+   *
+   * @param sdkMeterProviderBuilder the builder
+   */
+  public static void registerMetricReaderWithCardinalitySelector(
+      SdkMeterProviderBuilder sdkMeterProviderBuilder,
+      MetricReader metricReader,
+      CardinalityLimitSelector cardinalityLimitSelector) {
+    try {
+      Method method =
+          SdkMeterProviderBuilder.class.getDeclaredMethod(
+              "registerMetricReader", MetricReader.class, CardinalityLimitSelector.class);
+      method.setAccessible(true);
+      method.invoke(sdkMeterProviderBuilder, metricReader, cardinalityLimitSelector);
+    } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
+      throw new IllegalStateException(
+          "Error calling addMetricReader on SdkMeterProviderBuilder", e);
+    }
+  }
+
   /**
    * Reflectively add an {@link AttributesProcessor} to the {@link ViewBuilder} which appends
    * key-values from baggage to all measurements.
@@ -81,6 +105,21 @@ private static void addAttributesProcessor(
     }
   }
 
+  /**
+   * Reflectively set the {@code cardinalityLimit} on the {@link ViewBuilder}.
+   *
+   * @param viewBuilder the builder
+   */
+  public static void setCardinalityLimit(ViewBuilder viewBuilder, int cardinalityLimit) {
+    try {
+      Method method = ViewBuilder.class.getDeclaredMethod("setCardinalityLimit", int.class);
+      method.setAccessible(true);
+      method.invoke(viewBuilder, cardinalityLimit);
+    } catch (NoSuchMethodException | InvocationTargetException | IllegalAccessException e) {
+      throw new IllegalStateException("Error setting cardinalityLimit on ViewBuilder", e);
+    }
+  }
+
   /** Reflectively reset the {@link SdkMeterProvider}, clearing all registered instruments. */
   public static void resetForTest(SdkMeterProvider sdkMeterProvider) {
     try {

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/export/CardinalityLimitSelector.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics.internal.export;
+
+import io.opentelemetry.sdk.metrics.InstrumentType;
+import io.opentelemetry.sdk.metrics.SdkMeterProviderBuilder;
+import io.opentelemetry.sdk.metrics.export.MetricReader;
+import io.opentelemetry.sdk.metrics.internal.SdkMeterProviderUtil;
+import io.opentelemetry.sdk.metrics.internal.state.MetricStorage;
+
+/**
+ * Customize the {@link io.opentelemetry.sdk.metrics.export.MetricReader} cardinality limit as a
+ * function of {@link InstrumentType}. Register via {@link
+ * SdkMeterProviderUtil#registerMetricReaderWithCardinalitySelector(SdkMeterProviderBuilder,
+ * MetricReader, CardinalityLimitSelector)}.
+ *
+ * <p>This class is internal and is hence not for public use. Its APIs are unstable and can change
+ * at any time.
+ */
+@FunctionalInterface
+public interface CardinalityLimitSelector {
+
+  /**
+   * The default {@link CardinalityLimitSelector}, allowing each metric to have {@code 2000} points.
+   */
+  static CardinalityLimitSelector defaultCardinalityLimitSelector() {
+    return unused -> MetricStorage.DEFAULT_MAX_CARDINALITY;
+  }
+
+  /**
+   * Return the default cardinality limit for metrics from instruments of type {@code
+   * instrumentType}. The cardinality limit dictates the maximum number of distinct points (or time
+   * series) for the metric.
+   */
+  int getCardinalityLimit(InstrumentType instrumentType);
+}

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/state/AsynchronousMetricStorage.java

@@ -46,6 +46,7 @@ final class AsynchronousMetricStorage<T extends PointData, U extends ExemplarDat
   private final AggregationTemporality aggregationTemporality;
   private final Aggregator<T, U> aggregator;
   private final AttributesProcessor attributesProcessor;
+  private final int maxCardinality;
   private Map<Attributes, T> points = new HashMap<>();
   private Map<Attributes, T> lastPoints =
       new HashMap<>(); // Only populated if aggregationTemporality == DELTA
@@ -54,7 +55,8 @@ private AsynchronousMetricStorage(
       RegisteredReader registeredReader,
       MetricDescriptor metricDescriptor,
       Aggregator<T, U> aggregator,
-      AttributesProcessor attributesProcessor) {
+      AttributesProcessor attributesProcessor,
+      int maxCardinality) {
     this.registeredReader = registeredReader;
     this.metricDescriptor = metricDescriptor;
     this.aggregationTemporality =
@@ -63,6 +65,7 @@ private AsynchronousMetricStorage(
             .getAggregationTemporality(metricDescriptor.getSourceInstrument().getType());
     this.aggregator = aggregator;
     this.attributesProcessor = attributesProcessor;
+    this.maxCardinality = maxCardinality;
   }
 
   /**
@@ -83,7 +86,8 @@ static <T extends PointData, U extends ExemplarData> AsynchronousMetricStorage<T
         registeredReader,
         metricDescriptor,
         aggregator,
-        registeredView.getViewAttributesProcessor());
+        registeredView.getViewAttributesProcessor(),
+        registeredView.getCardinalityLimit());
   }
 
   /**
@@ -109,13 +113,13 @@ void record(Measurement measurement) {
   private void recordPoint(T point) {
     Attributes attributes = point.getAttributes();
 
-    if (points.size() >= MetricStorage.MAX_CARDINALITY) {
+    if (points.size() >= maxCardinality) {
       throttlingLogger.log(
           Level.WARNING,
           "Instrument "
               + metricDescriptor.getSourceInstrument().getName()
               + " has exceeded the maximum allowed cardinality ("
-              + MetricStorage.MAX_CARDINALITY
+              + maxCardinality
               + ").");
       return;
     }

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/state/DefaultSynchronousMetricStorage.java

@@ -50,14 +50,16 @@ public final class DefaultSynchronousMetricStorage<T extends PointData, U extend
   private final ConcurrentHashMap<Attributes, AggregatorHandle<T, U>> aggregatorHandles =
       new ConcurrentHashMap<>();
   private final AttributesProcessor attributesProcessor;
+  private final int maxCardinality;
   private final ConcurrentLinkedQueue<AggregatorHandle<T, U>> aggregatorHandlePool =
       new ConcurrentLinkedQueue<>();
 
   DefaultSynchronousMetricStorage(
       RegisteredReader registeredReader,
       MetricDescriptor metricDescriptor,
       Aggregator<T, U> aggregator,
-      AttributesProcessor attributesProcessor) {
+      AttributesProcessor attributesProcessor,
+      int maxCardinality) {
     this.registeredReader = registeredReader;
     this.metricDescriptor = metricDescriptor;
     this.aggregationTemporality =
@@ -66,6 +68,7 @@ public final class DefaultSynchronousMetricStorage<T extends PointData, U extend
             .getAggregationTemporality(metricDescriptor.getSourceInstrument().getType());
     this.aggregator = aggregator;
     this.attributesProcessor = attributesProcessor;
+    this.maxCardinality = maxCardinality;
   }
 
   // Visible for testing
@@ -97,13 +100,13 @@ private AggregatorHandle<T, U> getAggregatorHandle(Attributes attributes, Contex
     if (handle != null) {
       return handle;
     }
-    if (aggregatorHandles.size() >= MAX_CARDINALITY) {
+    if (aggregatorHandles.size() >= maxCardinality) {
       logger.log(
           Level.WARNING,
           "Instrument "
               + metricDescriptor.getSourceInstrument().getName()
               + " has exceeded the maximum allowed cardinality ("
-              + MAX_CARDINALITY
+              + maxCardinality
               + ").");
       return null;
     }
@@ -143,9 +146,9 @@ public MetricData collect(
           }
         });
 
-    // Trim pool down if needed. pool.size() will only exceed MAX_CARDINALITY if new handles are
+    // Trim pool down if needed. pool.size() will only exceed maxCardinality if new handles are
     // created during collection.
-    int toDelete = aggregatorHandlePool.size() - MAX_CARDINALITY;
+    int toDelete = aggregatorHandlePool.size() - maxCardinality;
     for (int i = 0; i < toDelete; i++) {
       aggregatorHandlePool.poll();
     }