Fix exemplars that have no tracing information (#10745)

Author: JamesNK

playground/Stress/Stress.ApiService/Program.cs

@@ -8,6 +8,7 @@
 using System.Threading.Channels;
 using System.Xml.Linq;
 using Microsoft.AspNetCore.Mvc;
+using OpenTelemetry.Metrics;
 using OpenTelemetry.Resources;
 using Stress.ApiService;
 
@@ -23,7 +24,12 @@
     .WithTracing(tracing => tracing
         .AddSource(TraceCreator.ActivitySourceName, ProducerConsumer.ActivitySourceName)
         .AddSource("Services.Api"))
-    .WithMetrics(metrics => metrics.AddMeter(TestMetrics.MeterName));
+    .WithMetrics(metrics =>
+    {
+        metrics.AddMeter(TestMetrics.MeterName);
+        metrics.SetExemplarFilter(ExemplarFilterType.AlwaysOn);
+
+    });
 builder.Services.AddSingleton<TestMetrics>();
 
 var app = builder.Build();
@@ -63,6 +69,18 @@
     return "Counter incremented";
 });
 
+app.MapGet("/exemplars-no-span", (TestMetrics metrics) =>
+{
+    var activity = Activity.Current;
+    Activity.Current = null;
+
+    metrics.RecordHistogram(Random.Shared.NextDouble(), new TagList());
+
+    Activity.Current = activity;
+
+    return "Exemplar recorded";
+});
+
 app.MapGet("/overflow-counter", (TestMetrics metrics) =>
 {
     // Emit measurements to ensure at least 2000 unique tag values are emitted,

playground/Stress/Stress.ApiService/TestMetrics.cs

@@ -12,6 +12,7 @@ public class TestMetrics : IDisposable
 
     private readonly Meter _meter;
     private readonly Counter<int> _counter;
+    private readonly Histogram<double> _histogram;
 
     public TestMetrics()
     {
@@ -25,6 +26,11 @@ public TestMetrics()
             new KeyValuePair<string, object?>("instrument-tag", Guid.NewGuid().ToString())
         ]);
 
+        _histogram = _meter.CreateHistogram<double>("test-histogram", unit: null, description: "This is a description", tags:
+        [
+            new KeyValuePair<string, object?>("instrument-tag", Guid.NewGuid().ToString())
+        ]);
+
         var uploadSpeed = new List<double>();
 
         Task.Run(async () =>
@@ -58,6 +64,11 @@ public void IncrementCounter(int value, in TagList tags)
         _counter.Add(value, in tags);
     }
 
+    public void RecordHistogram(double value, in TagList tags)
+    {
+        _histogram.Record(value, in tags);
+    }
+
     public void Dispose()
     {
         _meter.Dispose();

playground/Stress/Stress.AppHost/Program.cs

@@ -83,6 +83,7 @@
 serviceBuilder.WithHttpCommand("/multiple-traces-linked", "Multiple traces linked", commandOptions: new() { Method = HttpMethod.Get, IconName = "ContentViewGalleryLightning" });
 serviceBuilder.WithHttpCommand("/overflow-counter", "Overflow counter", commandOptions: new() { Method = HttpMethod.Get, IconName = "ContentViewGalleryLightning" });
 serviceBuilder.WithHttpCommand("/nested-trace-spans", "Out of order nested spans", commandOptions: new() { Method = HttpMethod.Get, IconName = "ContentViewGalleryLightning" });
+serviceBuilder.WithHttpCommand("/exemplars-no-span", "Examplars with no span", commandOptions: new() { Method = HttpMethod.Get, IconName = "ContentViewGalleryLightning" });
 
 builder.AddProject<Projects.Stress_TelemetryService>("stress-telemetryservice")
        .WithUrls(c => c.Urls.Add(new() { Url = "https://someplace.com", DisplayText = "Some place" }))

src/Aspire.Dashboard/Components/Controls/Chart/PlotlyChart.razor.cs

@@ -153,9 +153,22 @@ private PlotlyTrace CalculateExemplarsTrace(List<DateTimeOffset> xValues, List<C
 
         foreach (var exemplar in exemplarGroups.SelectMany(g => g.Value))
         {
-            var title = exemplar.Span != null
-                ? SpanWaterfallViewModel.GetTitle(exemplar.Span, Applications)
-                : $"{Loc[nameof(ControlsStrings.PlotlyChartTrace)]}: {OtlpHelpers.ToShortenedId(exemplar.TraceId)}";
+            string title;
+            if (exemplar.Span != null)
+            {
+                title = SpanWaterfallViewModel.GetTitle(exemplar.Span, Applications);
+            }
+            else if (!string.IsNullOrEmpty(exemplar.TraceId))
+            {
+                // Exemplar has trace information but isn't matched to a span in the system.
+                title = $"{Loc[nameof(ControlsStrings.PlotlyChartTrace)]}: {OtlpHelpers.ToShortenedId(exemplar.TraceId)}";
+            }
+            else
+            {
+                // Exemplar has no span information. Use generic title.
+                title = Loc[nameof(ControlsStrings.PlotlyChartExemplar)];
+            }
+
             var tooltip = FormatTooltip(title, exemplar.Value, exemplar.Start);
 
             exemplarTraceDto.X.Add(exemplar.Start);