Adding TraceSampling to Examplar Sampler

.gitignore

@@ -13,3 +13,7 @@ simpleclient_pushgateway/mockserver.log
 simpleclient_pushgateway/mockserver_request.log
 nb-configuration.xml
 dependency-reduced-pom.xml
+
+**/.classpath
+**.project
+**/.settings/

benchmarks/src/main/java/io/prometheus/client/benchmark/ExemplarsBenchmark.java

@@ -76,5 +76,10 @@ public String getTraceId() {
     public String getSpanId() {
       return "span-id";
     }
+
+    @Override
+    public boolean isSampled() {
+        return true;
+    }
   }
 }

integration_tests/it_exemplars_otel_agent/pom.xml

@@ -20,6 +20,13 @@
         <type>pom</type>
         <scope>import</scope>
       </dependency>
+      <dependency>
+        <groupId>io.prometheus</groupId>
+        <artifactId>simpleclient_bom</artifactId>
+        <version>${project.version}</version>
+        <type>pom</type>
+        <scope>import</scope>
+      </dependency>
     </dependencies>
   </dependencyManagement>
 
@@ -33,11 +40,6 @@
       <artifactId>okhttp</artifactId>
       <scope>compile</scope>
     </dependency>
-    <dependency>
-      <groupId>io.prometheus</groupId>
-      <artifactId>simpleclient</artifactId>
-      <version>${project.version}</version>
-    </dependency>
     <dependency>
       <groupId>io.prometheus</groupId>
       <artifactId>simpleclient_hotspot</artifactId>

integration_tests/it_exemplars_otel_agent/src/test/java/io/prometheus/client/it/exemplars_otel_agent/ExemplarsOpenTelemetryAgentIT.java

@@ -42,6 +42,7 @@ public ExemplarsOpenTelemetryAgentIT() throws IOException, URISyntaxException {
             "java",
             "-Dotel.traces.exporter=logging",
             "-Dotel.metrics.exporter=none",
+            "-Dotel.traces.sampler=always_on",
             "-javaagent:/app/" + agentJar,
             "-jar",
             "/app/" + appJar

simpleclient/src/main/java/io/prometheus/client/exemplars/DefaultExemplarSampler.java

@@ -41,8 +41,9 @@ public Exemplar sample(double value, double bucketFrom, double bucketTo, Exempla
 
   private Exemplar doSample(double value, Exemplar previous) {
     long timestampMs = clock.currentTimeMillis();
-    if (previous == null || previous.getTimestampMs() == null
-        || timestampMs - previous.getTimestampMs() > minRetentionIntervalMs) {
+    if ((previous == null || previous.getTimestampMs() == null
+        || timestampMs - previous.getTimestampMs() > minRetentionIntervalMs)
+        && spanContextSupplier.isSampled()) {
       String spanId = spanContextSupplier.getSpanId();
       String traceId = spanContextSupplier.getTraceId();
       if (traceId != null && spanId != null) {

simpleclient/src/test/java/io/prometheus/client/exemplars/DefaultExemplarSamplerTest.java

@@ -1,15 +1,16 @@
 package io.prometheus.client.exemplars;
 
-import io.prometheus.client.exemplars.tracer.common.SpanContextSupplier;
-import org.junit.Assert;
-import org.junit.Before;
-import org.junit.Test;
+import static java.lang.Double.NEGATIVE_INFINITY;
+import static java.lang.Double.POSITIVE_INFINITY;
 
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicReference;
 
-import static java.lang.Double.NEGATIVE_INFINITY;
-import static java.lang.Double.POSITIVE_INFINITY;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import io.prometheus.client.exemplars.tracer.common.SpanContextSupplier;
 
 public class DefaultExemplarSamplerTest {
 
@@ -20,6 +21,7 @@ public class DefaultExemplarSamplerTest {
   final AtomicReference<String> spanId = new AtomicReference<String>();
   final AtomicLong timestamp = new AtomicLong();
   DefaultExemplarSampler defaultSampler;
+  DefaultExemplarSampler defaultSamplerWithNoSample;
 
   final SpanContextSupplier testContext = new SpanContextSupplier() {
     @Override
@@ -31,7 +33,30 @@ public String getTraceId() {
     public String getSpanId() {
       return spanId.get();
     }
-  };
+
+        @Override
+        public boolean isSampled() {
+            return true;
+        }
+    };
+
+    final SpanContextSupplier testContextNoSample = new SpanContextSupplier() {
+
+        @Override
+        public String getTraceId() {
+            return traceId.get();
+        }
+
+        @Override
+        public String getSpanId() {
+            return spanId.get();
+        }
+
+        @Override
+        public boolean isSampled() {
+            return false;
+        }
+    };
 
   final DefaultExemplarSampler.Clock testClock = new DefaultExemplarSampler.Clock() {
     @Override
@@ -46,6 +71,7 @@ public void setUp() {
     spanId.set("span-1");
     timestamp.set(System.currentTimeMillis());
     defaultSampler = new DefaultExemplarSampler(testContext, testClock);
+    defaultSamplerWithNoSample = new DefaultExemplarSampler(testContextNoSample, testClock);
   }
 
   @Test
@@ -68,6 +94,18 @@ public void testCounter() {
     Assert.assertNull(sampler.sample(4.0, null));
   }
 
+  @Test
+  public void testCounterWithNoSample() {
+    CounterExemplarSampler sampler = defaultSamplerWithNoSample;
+    Assert.assertEquals(null, sampler.sample(2.0, null));
+  }
+
+  @Test
+  public void testHistogramWithNoSample() {
+    HistogramExemplarSampler sampler = defaultSamplerWithNoSample;
+    Assert.assertEquals(null, sampler.sample(2.0, NEGATIVE_INFINITY, POSITIVE_INFINITY, null));
+  }
+
   @Test
   public void testHistogram() {
     HistogramExemplarSampler sampler = defaultSampler;

simpleclient_bom/pom.xml

@@ -71,6 +71,11 @@
                 <artifactId>simpleclient_httpserver</artifactId>
                 <version>${project.version}</version>
             </dependency>
+            <dependency>
+                <groupId>io.prometheus</groupId>
+                <artifactId>simpleclient_tracer_common</artifactId>
+                <version>${project.version}</version>
+            </dependency>
             <dependency>
                 <groupId>io.prometheus</groupId>
                 <artifactId>simpleclient_jetty</artifactId>

simpleclient_tracer/simpleclient_tracer_common/src/main/java/io/prometheus/client/exemplars/tracer/common/SpanContextSupplier.java

@@ -11,4 +11,11 @@ public interface SpanContextSupplier {
    * @return the current span id, or {@code null} if this call is not happening within a span context.
    */
   String getSpanId();
+
+  /**
+   * @return the state of the current Span. If this value is false a component before in the chain take the decision to not record it. Subsequent calling service have
+   * to respect this value in order not to have partial TraceID with only some Span in it. This value is important to be sure to choose a recorded Trace in Examplar
+   * sampling process
+   */
+  boolean isSampled();
 }

simpleclient_tracer/simpleclient_tracer_otel/src/main/java/io/prometheus/client/exemplars/tracer/otel/OpenTelemetrySpanContextSupplier.java

@@ -7,14 +7,15 @@
 
 public class OpenTelemetrySpanContextSupplier implements SpanContextSupplier {
 
-  public static boolean isAvailable() {
+	public static boolean isAvailable() {
     try {
       if ("inactive".equalsIgnoreCase(System.getProperties().getProperty("io.prometheus.otelExemplars"))) {
         return false;
       }
       OpenTelemetrySpanContextSupplier test = new OpenTelemetrySpanContextSupplier();
       test.getSpanId();
       test.getTraceId();
+      test.isSampled();
       return true;
     } catch (LinkageError ignored) {
       // NoClassDefFoundError:
@@ -25,15 +26,20 @@ public static boolean isAvailable() {
     }
   }
 
-  @Override
-  public String getTraceId() {
-    String traceId = Span.current().getSpanContext().getTraceId();
-    return TraceId.isValid(traceId) ? traceId : null;
-  }
+	@Override
+	public String getTraceId() {
+		String traceId = Span.current().getSpanContext().getTraceId();
+		return TraceId.isValid(traceId) ? traceId : null;
+	}
 
-  @Override
-  public String getSpanId() {
-    String spanId = Span.current().getSpanContext().getSpanId();
-    return SpanId.isValid(spanId) ? spanId : null;
-  }
+	@Override
+	public String getSpanId() {
+		String spanId = Span.current().getSpanContext().getSpanId();
+		return SpanId.isValid(spanId) ? spanId : null;
+	}
+
+	@Override
+	public boolean isSampled() {
+		return Span.current().getSpanContext().isSampled();
+	}
 }

simpleclient_tracer/simpleclient_tracer_otel_agent/src/main/java/io/prometheus/client/exemplars/tracer/otel_agent/OpenTelemetryAgentSpanContextSupplier.java

@@ -20,6 +20,7 @@ public static boolean isAvailable() {
       OpenTelemetryAgentSpanContextSupplier test = new OpenTelemetryAgentSpanContextSupplier();
       test.getSpanId();
       test.getTraceId();
+      test.isSampled();
       return true;
     } catch (LinkageError ignored) {
       // NoClassDefFoundError:
@@ -41,4 +42,9 @@ public String getSpanId() {
     String spanId = Span.current().getSpanContext().getSpanId();
     return SpanId.isValid(spanId) ? spanId : null;
   }
+
+  @Override
+  public boolean isSampled() {
+    return Span.current().getSpanContext().isSampled();
+  }
 }