Exponential histogram example (#396)

Author: jaydeluca

metrics/build.gradle.kts

@@ -15,6 +15,6 @@ dependencies {
     implementation("io.opentelemetry:opentelemetry-api")
 
     implementation("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure")
-    runtimeOnly("io.opentelemetry:opentelemetry-exporter-otlp")
+    implementation("io.opentelemetry:opentelemetry-exporter-otlp")
     implementation("io.opentelemetry:opentelemetry-api-incubator")
 }

metrics/src/main/java/io/opentelemetry/example/metrics/ExponentialHistogramExample.java

@@ -0,0 +1,88 @@
+package io.opentelemetry.example.metrics;
+
+import static io.opentelemetry.api.common.AttributeKey.stringKey;
+
+import io.opentelemetry.api.OpenTelemetry;
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.metrics.LongHistogram;
+import io.opentelemetry.api.metrics.Meter;
+import io.opentelemetry.exporter.otlp.metrics.OtlpGrpcMetricExporter;
+import io.opentelemetry.sdk.OpenTelemetrySdk;
+import io.opentelemetry.sdk.metrics.Aggregation;
+import io.opentelemetry.sdk.metrics.InstrumentSelector;
+import io.opentelemetry.sdk.metrics.SdkMeterProvider;
+import io.opentelemetry.sdk.metrics.View;
+import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
+import java.time.Duration;
+import java.util.Random;
+
+/**
+ * Configures two histograms to use the base2ExponentialBucketHistogram aggregation, one that uses
+ * default configurations, and another that sets a custom maxScale.
+ */
+public class ExponentialHistogramExample {
+  private final OpenTelemetry otel;
+
+  public ExponentialHistogramExample(OpenTelemetry otel) {
+    this.otel = otel;
+  }
+
+  public static void main(String[] args) throws InterruptedException {
+    SdkMeterProvider sdkMeterProvider =
+        SdkMeterProvider.builder()
+            .registerView(
+                // Target histograms matching this name and apply a custom maxScale
+                InstrumentSelector.builder().setName("*custom_scale*").build(),
+                View.builder()
+                    .setAggregation(Aggregation.base2ExponentialBucketHistogram(160, 4))
+                    .build())
+            .registerView(
+                // Target this one histogram and use defaults (maxBuckets: 160 maxScale: 20)
+                InstrumentSelector.builder().setName("job.duration").build(),
+                View.builder()
+                    .setAggregation(Aggregation.base2ExponentialBucketHistogram())
+                    .build())
+            .registerMetricReader(
+                PeriodicMetricReader.builder(OtlpGrpcMetricExporter.builder().build())
+                    // Default is 60000ms (60 seconds). Set to 10 seconds for demonstrative purposes
+                    // only.
+                    .setInterval(Duration.ofSeconds(10))
+                    .build())
+            .build();
+
+    OpenTelemetry sdk = OpenTelemetrySdk.builder().setMeterProvider(sdkMeterProvider).build();
+
+    new ExponentialHistogramExample(sdk).run();
+  }
+
+  void run() throws InterruptedException {
+    Meter meter = otel.getMeter("io.opentelemetry.example.metrics");
+
+    LongHistogram histogram =
+        meter
+            .histogramBuilder("job.duration")
+            .ofLongs()
+            .setDescription("A distribution of job execution time")
+            .setUnit("seconds")
+            .build();
+
+    LongHistogram customScaleHistogram =
+        meter
+            .histogramBuilder("job2.custom_scale.duration")
+            .ofLongs()
+            .setDescription("A distribution of job2's execution time using a custom scale value.")
+            .setUnit("seconds")
+            .build();
+
+    Random rand = new Random();
+    Attributes attrs = Attributes.of(stringKey("job"), "update_database");
+    long metricPoint;
+
+    while (true) {
+      metricPoint = rand.nextLong(1000);
+      histogram.record(metricPoint, attrs);
+      customScaleHistogram.record(metricPoint, attrs);
+      Thread.sleep(1000);
+    }
+  }
+}