enable exemplars by default

CHANGELOG.md

@@ -8,6 +8,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Changed
+
+- Enable exemplars by default in `go.opentelemetry.io/otel/sdk/metric`. Exemplars can be disabled by setting `OTEL_METRICS_EXEMPLAR_FILTER=always_off` (#5778)
+
 ### Fixed
 
 - Fix memory leak in the global `MeterProvider` when identical instruments are repeatedly created. (#5754)

sdk/internal/x/x_test.go

@@ -10,7 +10,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestExemplars(t *testing.T) {
+func TestResource(t *testing.T) {
 	const key = "OTEL_GO_X_RESOURCE"
 	require.Equal(t, key, Resource.Key())
 

sdk/metric/exemplar.go

@@ -9,7 +9,6 @@ import (
 	"slices"
 
 	"go.opentelemetry.io/otel/sdk/metric/internal/exemplar"
-	"go.opentelemetry.io/otel/sdk/metric/internal/x"
 )
 
 // reservoirFunc returns the appropriately configured exemplar reservoir
@@ -20,9 +19,6 @@ import (
 // feature is enabled and the OTEL_METRICS_EXEMPLAR_FILTER environment variable
 // is not set to always_off.
 func reservoirFunc[N int64 | float64](agg Aggregation) func() exemplar.FilteredReservoir[N] {
-	if !x.Exemplars.Enabled() {
-		return nil
-	}
 	// https://github.com/open-telemetry/opentelemetry-specification/blob/d4b241f451674e8f611bb589477680341006ad2b/specification/configuration/sdk-environment-variables.md#exemplar
 	const filterEnvKey = "OTEL_METRICS_EXEMPLAR_FILTER"
 

sdk/metric/internal/x/x.go

@@ -10,39 +10,23 @@ package x // import "go.opentelemetry.io/otel/sdk/metric/internal/x"
 import (
 	"os"
 	"strconv"
-	"strings"
 )
 
-var (
-	// Exemplars is an experimental feature flag that defines if exemplars
-	// should be recorded for metric data-points.
-	//
-	// To enable this feature set the OTEL_GO_X_EXEMPLAR environment variable
-	// to the case-insensitive string value of "true" (i.e. "True" and "TRUE"
-	// will also enable this).
-	Exemplars = newFeature("EXEMPLAR", func(v string) (string, bool) {
-		if strings.ToLower(v) == "true" {
-			return v, true
-		}
-		return "", false
-	})
-
-	// CardinalityLimit is an experimental feature flag that defines if
-	// cardinality limits should be applied to the recorded metric data-points.
-	//
-	// To enable this feature set the OTEL_GO_X_CARDINALITY_LIMIT environment
-	// variable to the integer limit value you want to use.
-	//
-	// Setting OTEL_GO_X_CARDINALITY_LIMIT to a value less than or equal to 0
-	// will disable the cardinality limits.
-	CardinalityLimit = newFeature("CARDINALITY_LIMIT", func(v string) (int, bool) {
-		n, err := strconv.Atoi(v)
-		if err != nil {
-			return 0, false
-		}
-		return n, true
-	})
-)
+// CardinalityLimit is an experimental feature flag that defines if
+// cardinality limits should be applied to the recorded metric data-points.
+//
+// To enable this feature set the OTEL_GO_X_CARDINALITY_LIMIT environment
+// variable to the integer limit value you want to use.
+//
+// Setting OTEL_GO_X_CARDINALITY_LIMIT to a value less than or equal to 0
+// will disable the cardinality limits.
+var CardinalityLimit = newFeature("CARDINALITY_LIMIT", func(v string) (int, bool) {
+	n, err := strconv.Atoi(v)
+	if err != nil {
+		return 0, false
+	}
+	return n, true
+})
 
 // Feature is an experimental feature control flag. It provides a uniform way
 // to interact with these feature flags and parse their values.

sdk/metric/internal/x/x_test.go

@@ -10,18 +10,6 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestExemplars(t *testing.T) {
-	const key = "OTEL_GO_X_EXEMPLAR"
-	require.Equal(t, key, Exemplars.Key())
-
-	t.Run("true", run(setenv(key, "true"), assertEnabled(Exemplars, "true")))
-	t.Run("True", run(setenv(key, "True"), assertEnabled(Exemplars, "True")))
-	t.Run("TRUE", run(setenv(key, "TRUE"), assertEnabled(Exemplars, "TRUE")))
-	t.Run("false", run(setenv(key, "false"), assertDisabled(Exemplars)))
-	t.Run("1", run(setenv(key, "1"), assertDisabled(Exemplars)))
-	t.Run("empty", run(assertDisabled(Exemplars)))
-}
-
 func TestCardinalityLimit(t *testing.T) {
 	const key = "OTEL_GO_X_CARDINALITY_LIMIT"
 	require.Equal(t, key, CardinalityLimit.Key())

sdk/metric/pipeline_test.go

@@ -448,59 +448,46 @@ func TestExemplars(t *testing.T) {
 	})
 	sampled := trace.ContextWithSpanContext(context.Background(), sc)
 
-	t.Run("OTEL_GO_X_EXEMPLAR=true", func(t *testing.T) {
-		t.Setenv("OTEL_GO_X_EXEMPLAR", "true")
-
-		t.Run("Default", func(t *testing.T) {
-			m, r := setup("default")
-			measure(ctx, m)
-			check(t, r, 0, 0, 0)
-
-			measure(sampled, m)
-			check(t, r, nCPU, 1, 20)
-		})
-
-		t.Run("Invalid", func(t *testing.T) {
-			t.Setenv("OTEL_METRICS_EXEMPLAR_FILTER", "unrecognized")
-			m, r := setup("default")
-			measure(ctx, m)
-			check(t, r, 0, 0, 0)
-
-			measure(sampled, m)
-			check(t, r, nCPU, 1, 20)
-		})
-
-		t.Run("always_on", func(t *testing.T) {
-			t.Setenv("OTEL_METRICS_EXEMPLAR_FILTER", "always_on")
-			m, r := setup("always_on")
-			measure(ctx, m)
-			check(t, r, nCPU, 1, 20)
-		})
+	t.Run("Default", func(t *testing.T) {
+		m, r := setup("default")
+		measure(ctx, m)
+		check(t, r, 0, 0, 0)
 
-		t.Run("always_off", func(t *testing.T) {
-			t.Setenv("OTEL_METRICS_EXEMPLAR_FILTER", "always_off")
-			m, r := setup("always_off")
-			measure(ctx, m)
-			check(t, r, 0, 0, 0)
-		})
+		measure(sampled, m)
+		check(t, r, nCPU, 1, 20)
+	})
 
-		t.Run("trace_based", func(t *testing.T) {
-			t.Setenv("OTEL_METRICS_EXEMPLAR_FILTER", "trace_based")
-			m, r := setup("trace_based")
-			measure(ctx, m)
-			check(t, r, 0, 0, 0)
+	t.Run("Invalid", func(t *testing.T) {
+		t.Setenv("OTEL_METRICS_EXEMPLAR_FILTER", "unrecognized")
+		m, r := setup("default")
+		measure(ctx, m)
+		check(t, r, 0, 0, 0)
 
-			measure(sampled, m)
-			check(t, r, nCPU, 1, 20)
-		})
+		measure(sampled, m)
+		check(t, r, nCPU, 1, 20)
 	})
 
-	t.Run("OTEL_GO_X_EXEMPLAR=false", func(t *testing.T) {
-		t.Setenv("OTEL_GO_X_EXEMPLAR", "false")
-
+	t.Run("always_on", func(t *testing.T) {
 		t.Setenv("OTEL_METRICS_EXEMPLAR_FILTER", "always_on")
 		m, r := setup("always_on")
 		measure(ctx, m)
+		check(t, r, nCPU, 1, 20)
+	})
+
+	t.Run("always_off", func(t *testing.T) {
+		t.Setenv("OTEL_METRICS_EXEMPLAR_FILTER", "always_off")
+		m, r := setup("always_off")
+		measure(ctx, m)
+		check(t, r, 0, 0, 0)
+	})
+
+	t.Run("trace_based", func(t *testing.T) {
+		t.Setenv("OTEL_METRICS_EXEMPLAR_FILTER", "trace_based")
+		m, r := setup("trace_based")
+		measure(ctx, m)
 		check(t, r, 0, 0, 0)
+
+		measure(sampled, m)
+		check(t, r, nCPU, 1, 20)
 	})
 }