Change initial sampler to 5% random to match x-ray docs and add jitter to polling. (#50)

Author: Anuraag Agrawal

aws-xray/src/main/java/io/opentelemetry/contrib/awsxray/AwsXrayRemoteSampler.java

@@ -25,6 +25,8 @@
 /** Remote sampler that gets sampling configuration from AWS X-Ray. */
 public final class AwsXrayRemoteSampler implements Sampler, Closeable {
 
+  private static final Random RANDOM = new Random();
+
   private static final Logger logger = Logger.getLogger(AwsXrayRemoteSampler.class.getName());
 
   private static final String WORKER_THREAD_NAME =
@@ -37,8 +39,10 @@ public final class AwsXrayRemoteSampler implements Sampler, Closeable {
   private final Sampler initialSampler;
   private final XraySamplerClient client;
   private final ScheduledExecutorService executor;
-  private final ScheduledFuture<?> pollFuture;
+  private final long pollingIntervalNanos;
+  private final int jitterNanos;
 
+  @Nullable private volatile ScheduledFuture<?> pollFuture;
   @Nullable private volatile GetSamplingRulesResponse previousRulesResponse;
   private volatile Sampler sampler;
 
@@ -72,9 +76,12 @@ public static AwsXrayRemoteSamplerBuilder newBuilder(Resource resource) {
 
     sampler = initialSampler;
 
-    pollFuture =
-        executor.scheduleAtFixedRate(
-            this::getAndUpdateSampler, 0, pollingIntervalNanos, TimeUnit.NANOSECONDS);
+    this.pollingIntervalNanos = pollingIntervalNanos;
+    // Add ~1% of jitter. Truncating to int is safe for any practical polling interval.
+    jitterNanos = (int) (pollingIntervalNanos / 100);
+
+    // Execute first update right away on the executor thread.
+    executor.execute(this::getAndUpdateSampler);
   }
 
   @Override
@@ -106,11 +113,20 @@ private void getAndUpdateSampler() {
     } catch (Throwable t) {
       logger.log(Level.FINE, "Failed to update sampler", t);
     }
+    scheduleSamplerUpdate();
+  }
+
+  private void scheduleSamplerUpdate() {
+    long delay = pollingIntervalNanos + RANDOM.nextInt(jitterNanos);
+    pollFuture = executor.schedule(this::getAndUpdateSampler, delay, TimeUnit.NANOSECONDS);
   }
 
   @Override
   public void close() {
-    pollFuture.cancel(true);
+    ScheduledFuture<?> pollFuture = this.pollFuture;
+    if (pollFuture != null) {
+      pollFuture.cancel(true);
+    }
     executor.shutdownNow();
     // No flushing behavior so no need to wait for the shutdown.
   }

aws-xray/src/main/java/io/opentelemetry/contrib/awsxray/AwsXrayRemoteSamplerBuilder.java

@@ -20,7 +20,7 @@ public final class AwsXrayRemoteSamplerBuilder {
   private final Resource resource;
 
   private String endpoint = DEFAULT_ENDPOINT;
-  private Sampler initialSampler = Sampler.parentBased(Sampler.alwaysOn());
+  private Sampler initialSampler = Sampler.parentBased(Sampler.traceIdRatioBased(0.05));
   private long pollingIntervalNanos = TimeUnit.SECONDS.toNanos(DEFAULT_POLLING_INTERVAL_SECS);
 
   AwsXrayRemoteSamplerBuilder(Resource resource) {

aws-xray/src/test/java/io/opentelemetry/contrib/awsxray/AwsXrayRemoteSamplerTest.java

@@ -183,7 +183,8 @@ void getAndUpdate() {
   }
 
   @Test
-  void initialSampler() {
-    assertThat(sampler.getDescription()).isEqualTo("AwsXrayRemoteSampler{AlwaysOnSampler}");
+  void defaultInitialSampler() {
+    assertThat(AwsXrayRemoteSampler.newBuilder(Resource.empty()).build().getDescription())
+        .startsWith("AwsXrayRemoteSampler{ParentBased{root:TraceIdRatioBased{0.050000}");
   }
 }