Merge branch 'feature/resource-attribute-tags' of https://github.com/…

…robertcoltheart/opentelemetry-dotnet into feature/resource-attribute-tags

docs/logs/README.md

@@ -107,6 +107,21 @@ Here is the rule of thumb:
   Minutes - Console Application](./getting-started-console/README.md) tutorial
   to learn more.
 
+:heavy_check_mark: You should use dot-separated
+[UpperCamelCase](https://en.wikipedia.org/wiki/Camel_case) as the log category
+name, which makes it convenient to [filter logs](#log-filtering). A common
+practice is to use fully qualified class name, and if further categorization is
+desired, append a subcategory name. Refer to the [.NET official
+document](https://learn.microsoft.com/dotnet/core/extensions/logging#log-category)
+to learn more.
+
+```csharp
+loggerFactory.CreateLogger<MyClass>(); // this is equivalent to CreateLogger("MyProduct.MyLibrary.MyClass")
+loggerFactory.CreateLogger("MyProduct.MyLibrary.MyClass"); // use the fully qualified class name
+loggerFactory.CreateLogger("MyProduct.MyLibrary.MyClass.DatabaseOperations"); // append a subcategory name
+loggerFactory.CreateLogger("MyProduct.MyLibrary.MyClass.FileOperations"); // append another subcategory name
+```
+
 :stop_sign: You should avoid creating loggers too frequently. Although loggers
 are not super expensive, they still come with CPU and memory cost, and are meant
 to be reused throughout the application. Refer to the [logging performance
@@ -186,11 +201,6 @@ instances if they are created by you.
   API invocation associated with the logger factory could become no-op (i.e. no
   logs will be emitted).
 
-:heavy_check_mark: You should use the fully qualified class name as the log
-category name. Refer to the [.NET official
-document](https://learn.microsoft.com/dotnet/core/extensions/logging#log-category)
-to learn more.
-
 ## Log Correlation
 
 In OpenTelemetry, logs are automatically correlated to

docs/metrics/customizing-the-sdk/README.md

@@ -412,58 +412,38 @@ exemplars.
 
 #### ExemplarFilter
 
-`ExemplarFilter` determines which measurements are eligible to become an
-Exemplar. i.e. `ExemplarFilter` determines which measurements are offered to
-`ExemplarReservoir`, which makes the final decision about whether the offered
-measurement gets stored as an exemplar. They can be used to control the noise
-and overhead associated with Exemplar collection.
+`ExemplarFilter` determines which measurements are offered to the configured
+`ExemplarReservoir`, which makes the final decision about whether or not the
+offered measurement gets recorded as an `Exemplar`. Generally `ExemplarFilter`
+is a mechanism to control the overhead associated with `Exemplar` offering.
 
-OpenTelemetry SDK comes with the following Filters:
+OpenTelemetry SDK comes with the following `ExemplarFilters` (defined on
+`ExemplarFilterType`):
 
-* `AlwaysOnExemplarFilter` - makes all measurements eligible for being an Exemplar.
-* `AlwaysOffExemplarFilter` - makes no measurements eligible for being an
-  Exemplar. Using this is as good as turning off Exemplar feature, and is the current
+* `AlwaysOff`: Makes no measurements eligible for becoming an `Exemplar`. Using
+  this is as good as turning off the `Exemplar` feature and is the current
   default.
-* `TraceBasedExemplarFilter` - makes those measurements eligible for being an
-Exemplar, which are recorded in the context of a sampled parent `Activity`
-(span).
+* `AlwaysOn`: Makes all measurements eligible for becoming an `Exemplar`.
+* `TraceBased`: Makes those measurements eligible for becoming an `Exemplar`
+  which are recorded in the context of a sampled `Activity` (span).
 
-`SetExemplarFilter` method on `MeterProviderBuilder` can be used to set the
-desired `ExemplarFilter`.
-
-The snippet below shows how to set `ExemplarFilter`.
+The `SetExemplarFilter` extension method on `MeterProviderBuilder` can be used
+to set the desired `ExemplarFilterType` and enable `Exemplar` collection:
 
 ```csharp
 using OpenTelemetry;
 using OpenTelemetry.Metrics;
 
 using var meterProvider = Sdk.CreateMeterProviderBuilder()
     // rest of config not shown
-    .SetExemplarFilter(new TraceBasedExemplarFilter())
+    .SetExemplarFilter(ExemplarFilterType.TraceBased)
     .Build();
 ```
 
-> [!NOTE]
-> As of today, there is no separate toggle for enable/disable Exemplar feature.
-Exemplars can be disabled by setting filter as `AlwaysOffExemplarFilter`, which
-is also the default (i.e Exemplar feature is disabled by default). Users can
-enable the feature by setting filter to anything other than
-`AlwaysOffExemplarFilter`. For example: `.SetExemplarFilter(new TraceBasedExemplarFilter())`.
-
-If the built-in `ExemplarFilter`s are not meeting the needs, one may author
-custom `ExemplarFilter` as shown
-[here](../extending-the-sdk/README.md#exemplarfilter). A custom filter, which
-eliminates all un-interesting measurements from becoming Exemplar is a
-recommended way to control performance overhead associated with collecting
-Exemplars. See
-[benchmark](../../../test/Benchmarks/Metrics/ExemplarBenchmarks.cs) to see how
-much impact can `ExemplarFilter` have on performance.
-
 #### ExemplarReservoir
 
-`ExemplarReservoir` receives the measurements sampled in by the `ExemplarFilter`
-and is responsible for storing Exemplars. `ExemplarReservoir` ultimately decides
-which measurements get stored as exemplars. The following are the default
+`ExemplarReservoir` receives the measurements sampled by the `ExemplarFilter`
+and is responsible for recording `Exemplar`s. The following are the default
 reservoirs:
 
 * `AlignedHistogramBucketExemplarReservoir` is the default reservoir used for
@@ -479,7 +459,7 @@ size (currently defaulting to 1) determines the maximum number of exemplars
 stored.
 
 > [!NOTE]
-> Currently there is no ability to change or configure Reservoir.
+> Currently there is no ability to change or configure `ExemplarReservoir`.
 
 ### Instrumentation
 

docs/metrics/extending-the-sdk/README.md

@@ -74,44 +74,7 @@ Not supported.
 
 ## ExemplarFilter
 
-OpenTelemetry .NET SDK has provided the following built-in `ExemplarFilter`s:
-
-* [AlwaysOnExemplarFilter](../../../src/OpenTelemetry/Metrics/Exemplar/AlwaysOnExemplarFilter.cs)
-* [AlwaysOffExemplarFilter](../../../src/OpenTelemetry/Metrics/Exemplar/AlwaysOffExemplarFilter.cs)
-* [TraceBasedExemplarFilter](../../../src/OpenTelemetry/Metrics/Exemplar/TraceBasedExemplarFilter.cs)
-
-Custom exemplar filters can be implemented to achieve filtering based on other criterion:
-
-* `ExemplarFilter` should derive from `OpenTelemetry.ExemplarFilter` (which
-  belongs to the [OpenTelemetry](../../../src/OpenTelemetry/README.md) package)
-  and implement the `ShouldSample` method.
-
-One example is a filter, which filters all measurements of value lower
-than given threshold is given below. Such a filter prevents any measurements
-below the given threshold from ever becoming a `Exemplar`. Such filters could
-also incorporate the `TraceBasedExemplarFilter` condition as well, as storing
-exemplars for non-sampled traces may be undesired.
-
-```csharp
-public sealed class HighValueFilter : ExemplarFilter
-{
-    private readonly double maxValue;
-
-    public HighValueFilter(double maxValue)
-    {
-        this.maxValue = maxValue;
-    }
-    public override bool ShouldSample(long value, ReadOnlySpan<KeyValuePair<string, object>> tags)
-    {
-        return Activity.Current?.Recorded && value > this.maxValue;
-    }
-
-    public override bool ShouldSample(double value, ReadOnlySpan<KeyValuePair<string, object>> tags)
-    {
-        return Activity.Current?.Recorded && value > this.maxValue;
-    }
-}
-```
+Not supported.
 
 ## ExemplarReservoir
 

examples/AspNetCore/Program.cs

@@ -85,7 +85,7 @@
         builder
             .AddMeter(Instrumentation.MeterName)
 #if EXPOSE_EXPERIMENTAL_FEATURES
-            .SetExemplarFilter(new TraceBasedExemplarFilter())
+            .SetExemplarFilter(ExemplarFilterType.TraceBased)
 #endif
             .AddRuntimeInstrumentation()
             .AddHttpClientInstrumentation()

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md

@@ -30,6 +30,11 @@
   as it is mandated by the specification.
   ([#5316](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5268))
 
+* **Experimental (pre-release builds only):** Add support in
+  `OtlpMetricExporter` for emitting exemplars supplied on Counters, Gauges, and
+  ExponentialHistograms.
+  ([#5397](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5397))
+
 ## 1.7.0
 
 Released 2023-Dec-08

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/MetricItemExtensions.cs

@@ -158,6 +158,16 @@ internal static OtlpMetrics.Metric ToOtlpMetric(this Metric metric)
                         AddAttributes(metricPoint.Tags, dataPoint.Attributes);
 
                         dataPoint.AsInt = metricPoint.GetSumLong();
+
+                        if (metricPoint.TryGetExemplars(out var exemplars))
+                        {
+                            foreach (ref readonly var exemplar in exemplars)
+                            {
+                                dataPoint.Exemplars.Add(
+                                    ToOtlpExemplar(exemplar.LongValue, in exemplar));
+                            }
+                        }
+
                         sum.DataPoints.Add(dataPoint);
                     }
 
@@ -185,6 +195,16 @@ internal static OtlpMetrics.Metric ToOtlpMetric(this Metric metric)
                         AddAttributes(metricPoint.Tags, dataPoint.Attributes);
 
                         dataPoint.AsDouble = metricPoint.GetSumDouble();
+
+                        if (metricPoint.TryGetExemplars(out var exemplars))
+                        {
+                            foreach (ref readonly var exemplar in exemplars)
+                            {
+                                dataPoint.Exemplars.Add(
+                                    ToOtlpExemplar(exemplar.DoubleValue, in exemplar));
+                            }
+                        }
+
                         sum.DataPoints.Add(dataPoint);
                     }
 
@@ -206,6 +226,16 @@ internal static OtlpMetrics.Metric ToOtlpMetric(this Metric metric)
                         AddAttributes(metricPoint.Tags, dataPoint.Attributes);
 
                         dataPoint.AsInt = metricPoint.GetGaugeLastValueLong();
+
+                        if (metricPoint.TryGetExemplars(out var exemplars))
+                        {
+                            foreach (ref readonly var exemplar in exemplars)
+                            {
+                                dataPoint.Exemplars.Add(
+                                    ToOtlpExemplar(exemplar.LongValue, in exemplar));
+                            }
+                        }
+
                         gauge.DataPoints.Add(dataPoint);
                     }
 
@@ -227,6 +257,16 @@ internal static OtlpMetrics.Metric ToOtlpMetric(this Metric metric)
                         AddAttributes(metricPoint.Tags, dataPoint.Attributes);
 
                         dataPoint.AsDouble = metricPoint.GetGaugeLastValueDouble();
+
+                        if (metricPoint.TryGetExemplars(out var exemplars))
+                        {
+                            foreach (ref readonly var exemplar in exemplars)
+                            {
+                                dataPoint.Exemplars.Add(
+                                    ToOtlpExemplar(exemplar.DoubleValue, in exemplar));
+                            }
+                        }
+
                         gauge.DataPoints.Add(dataPoint);
                     }
 
@@ -320,7 +360,14 @@ internal static OtlpMetrics.Metric ToOtlpMetric(this Metric metric)
                             dataPoint.Positive.BucketCounts.Add((ulong)bucketCount);
                         }
 
-                        // TODO: exemplars.
+                        if (metricPoint.TryGetExemplars(out var exemplars))
+                        {
+                            foreach (ref readonly var exemplar in exemplars)
+                            {
+                                dataPoint.Exemplars.Add(
+                                    ToOtlpExemplar(exemplar.DoubleValue, in exemplar));
+                            }
+                        }
 
                         histogram.DataPoints.Add(dataPoint);
                     }
@@ -333,29 +380,7 @@ internal static OtlpMetrics.Metric ToOtlpMetric(this Metric metric)
         return otlpMetric;
     }
 
-    private static void AddAttributes(ReadOnlyTagCollection tags, RepeatedField<OtlpCommon.KeyValue> attributes)
-    {
-        foreach (var tag in tags)
-        {
-            if (OtlpKeyValueTransformer.Instance.TryTransformTag(tag, out var result))
-            {
-                attributes.Add(result);
-            }
-        }
-    }
-
-    private static void AddScopeAttributes(IEnumerable<KeyValuePair<string, object>> meterTags, RepeatedField<OtlpCommon.KeyValue> attributes)
-    {
-        foreach (var tag in meterTags)
-        {
-            if (OtlpKeyValueTransformer.Instance.TryTransformTag(tag, out var result))
-            {
-                attributes.Add(result);
-            }
-        }
-    }
-
-    private static OtlpMetrics.Exemplar ToOtlpExemplar<T>(T value, in Metrics.Exemplar exemplar)
+    internal static OtlpMetrics.Exemplar ToOtlpExemplar<T>(T value, in Metrics.Exemplar exemplar)
         where T : struct
     {
         var otlpExemplar = new OtlpMetrics.Exemplar
@@ -399,4 +424,26 @@ private static OtlpMetrics.Exemplar ToOtlpExemplar<T>(T value, in Metrics.Exempl
 
         return otlpExemplar;
     }
+
+    private static void AddAttributes(ReadOnlyTagCollection tags, RepeatedField<OtlpCommon.KeyValue> attributes)
+    {
+        foreach (var tag in tags)
+        {
+            if (OtlpKeyValueTransformer.Instance.TryTransformTag(tag, out var result))
+            {
+                attributes.Add(result);
+            }
+        }
+    }
+
+    private static void AddScopeAttributes(IEnumerable<KeyValuePair<string, object>> meterTags, RepeatedField<OtlpCommon.KeyValue> attributes)
+    {
+        foreach (var tag in meterTags)
+        {
+            if (OtlpKeyValueTransformer.Instance.TryTransformTag(tag, out var result))
+            {
+                attributes.Add(result);
+            }
+        }
+    }
 }