View - support for dropping instrument (#2449)

docs/metrics/customizing-the-sdk/Program.cs

@@ -34,7 +34,7 @@ public class Program
             .AddView(instrumentName: "MyCounter", name: "MyCounterRenamed")
 
             // Change Histogram bounds
-            .AddView(instrumentName: "MyHistogram", new HistogramConfiguration() { BucketBounds = new double[] { 10, 20 }, Aggregation = Aggregation.LastValue })
+            .AddView(instrumentName: "MyHistogram", new HistogramConfiguration() { BucketBounds = new double[] { 10, 20 } })
 
             // For the instrument "MyCounterCustomTags", aggregate with only the keys "tag1", "tag2".
             .AddView(instrumentName: "MyCounterCustomTags", new MetricStreamConfiguration() { TagKeys = new string[] { "tag1", "tag2" } })

src/OpenTelemetry/Metrics/DropConfiguration.cs

@@ -0,0 +1,35 @@
+// <copyright file="DropConfiguration.cs" company="OpenTelemetry Authors">
+// 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.
+// </copyright>
+
+using System;
+
+namespace OpenTelemetry.Metrics
+{
+    internal class DropConfiguration : MetricStreamConfiguration
+    {
+        private Aggregation aggregation = Aggregation.Drop;
+
+        public override Aggregation Aggregation
+        {
+            get => this.aggregation;
+
+            set
+            {
+                throw new ArgumentException($"Aggregation cannot be set.");
+            }
+        }
+    }
+}

src/OpenTelemetry/Metrics/MeterProviderBuilderExtensions.cs

@@ -66,14 +66,14 @@ namespace OpenTelemetry.Metrics
         /// </summary>
         /// <param name="meterProviderBuilder"><see cref="MeterProviderBuilder"/>.</param>
         /// <param name="instrumentName">Name of the instrument, to be used as part of Instrument selection criteria.</param>
-        /// <param name="aggregationConfig">Aggregation configuration used to produce metrics stream.</param>
+        /// <param name="metricStreamConfiguration">Aggregation configuration used to produce metrics stream.</param>
         /// <returns><see cref="MeterProvider"/>.</returns>
         /// <remarks>See View specification here : https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#view.</remarks>
-        public static MeterProviderBuilder AddView(this MeterProviderBuilder meterProviderBuilder, string instrumentName, MetricStreamConfiguration aggregationConfig)
+        public static MeterProviderBuilder AddView(this MeterProviderBuilder meterProviderBuilder, string instrumentName, MetricStreamConfiguration metricStreamConfiguration)
         {
             if (meterProviderBuilder is MeterProviderBuilderBase meterProviderBuilderBase)
             {
-                return meterProviderBuilderBase.AddView(instrumentName, aggregationConfig);
+                return meterProviderBuilderBase.AddView(instrumentName, metricStreamConfiguration);
             }
 
             return meterProviderBuilder;

src/OpenTelemetry/Metrics/MeterProviderSdk.cs

@@ -145,6 +145,14 @@ namespace OpenTelemetry.Metrics
                                     continue;
                                 }
 
+                                if (metricStreamConfig?.Aggregation == Aggregation.None)
+                                {
+                                    // TODO: Log that instrument is ignored
+                                    // as user explicitly asked to drop it
+                                    // with View.
+                                    continue;
+                                }
+
                                 var index = ++this.metricIndex;
                                 if (index >= MaxMetrics)
                                 {

src/OpenTelemetry/Metrics/MetricStreamConfiguration.cs

@@ -31,6 +31,8 @@ namespace OpenTelemetry.Metrics
 
     public class MetricStreamConfiguration
     {
+        public static readonly MetricStreamConfiguration Drop = new DropConfiguration();
+
         public string Name { get; set; }
 
         public string Description { get; set; }

test/OpenTelemetry.Tests.Stress.Metrics/Program.cs

@@ -15,7 +15,6 @@
 // </copyright>
 
 using System;
-using System.Diagnostics;
 using System.Diagnostics.Metrics;
 using System.Runtime.CompilerServices;
 using System.Threading;

test/OpenTelemetry.Tests/Metrics/MetricViewTests.cs

@@ -292,6 +292,86 @@ namespace OpenTelemetry.Metrics.Tests
             // Single point expected.
             Assert.Single(metricPoints);
         }
+
+        [Fact]
+        public void ViewToDropSingleInstrument()
+        {
+            using var meter = new Meter("ViewToDropSingleInstrumentTest");
+            var exportedItems = new List<Metric>();
+            using var meterProvider = Sdk.CreateMeterProviderBuilder()
+                .AddSource(meter.Name)
+                .AddView("counterNotInteresting", new MetricStreamConfiguration() { Aggregation = Aggregation.Drop })
+                .AddInMemoryExporter(exportedItems)
+                .Build();
+
+            // Expecting one metric stream.
+            var counterInteresting = meter.CreateCounter<long>("counterInteresting");
+            var counterNotInteresting = meter.CreateCounter<long>("counterNotInteresting");
+            counterInteresting.Add(10);
+            counterNotInteresting.Add(10);
+
+            meterProvider.ForceFlush(MaxTimeToAllowForFlush);
+            Assert.Single(exportedItems);
+            var metric = exportedItems[0];
+            Assert.Equal("counterInteresting", metric.Name);
+        }
+
+        [Fact]
+        public void ViewToDropMultipleInstruments()
+        {
+            using var meter = new Meter("ViewToDropMultipleInstrumentsTest");
+            var exportedItems = new List<Metric>();
+            using var meterProvider = Sdk.CreateMeterProviderBuilder()
+                .AddSource(meter.Name)
+                .AddView("server*", new MetricStreamConfiguration() { Aggregation = Aggregation.Drop })
+                .AddInMemoryExporter(exportedItems)
+                .Build();
+
+            // Expecting two client metric streams as both server* are dropped.
+            var serverRequests = meter.CreateCounter<long>("server.requests");
+            var serverExceptions = meter.CreateCounter<long>("server.exceptions");
+            var clientRequests = meter.CreateCounter<long>("client.requests");
+            var clientExceptions = meter.CreateCounter<long>("client.exceptions");
+            serverRequests.Add(10);
+            serverExceptions.Add(10);
+            clientRequests.Add(10);
+            clientExceptions.Add(10);
+
+            meterProvider.ForceFlush(MaxTimeToAllowForFlush);
+            Assert.Equal(2, exportedItems.Count);
+            Assert.Equal("client.requests", exportedItems[0].Name);
+            Assert.Equal("client.exceptions", exportedItems[1].Name);
+        }
+
+        [Fact]
+        public void ViewToDropAndRetainInstrument()
+        {
+            using var meter = new Meter("ViewToDropAndRetainInstrumentTest");
+            var exportedItems = new List<Metric>();
+            using var meterProvider = Sdk.CreateMeterProviderBuilder()
+                .AddSource(meter.Name)
+                .AddView("server.requests", MetricStreamConfiguration.Drop)
+                .AddView("server.requests", "server.request_renamed")
+                .AddInMemoryExporter(exportedItems)
+                .Build();
+
+            // Expecting one metric stream even though a View is asking
+            // to drop the instrument, because another View is matching
+            // the instrument, which asks to aggregate with defaults
+            // and a use a new name for the resulting metric.
+            var serverRequests = meter.CreateCounter<long>("server.requests");
+            serverRequests.Add(10);
+
+            meterProvider.ForceFlush(MaxTimeToAllowForFlush);
+            Assert.Single(exportedItems);
+            Assert.Equal("server.request_renamed", exportedItems[0].Name);
+        }
+
+        [Fact]
+        public void MetricStreamConfigurationForDropMustNotAllowOverriding()
+        {
+            Assert.Throws<ArgumentException>(() => MetricStreamConfiguration.Drop.Aggregation = Aggregation.Histogram);
+        }
     }
 #pragma warning restore SA1000 // KeywordsMustBeSpacedCorrectly
 }