diff --git a/dd-trace-core/src/main/java/datadog/trace/core/CoreTracer.java b/dd-trace-core/src/main/java/datadog/trace/core/CoreTracer.java index 7ad4497beca..ba5d454c619 100644 --- a/dd-trace-core/src/main/java/datadog/trace/core/CoreTracer.java +++ b/dd-trace-core/src/main/java/datadog/trace/core/CoreTracer.java @@ -2031,7 +2031,9 @@ protected static final DDSpanContext buildSpanContext( requestContextDataIast = null; ciVisibilityContextData = null; } - propagationTags = tracer.propagationTagsFactory.empty(); + // Local children share the parent's PropagationTags (trace-level state; reads route to the + // root) instead of allocating an unused empty() per span. + propagationTags = ddsc.getPropagationTags(); } else { long endToEndStartTime; diff --git a/dd-trace-core/src/main/java/datadog/trace/core/DDSpanContext.java b/dd-trace-core/src/main/java/datadog/trace/core/DDSpanContext.java index 6120502ec09..394a721fdd9 100644 --- a/dd-trace-core/src/main/java/datadog/trace/core/DDSpanContext.java +++ b/dd-trace-core/src/main/java/datadog/trace/core/DDSpanContext.java @@ -1238,14 +1238,22 @@ void processTagsAndBaggage( // Baggage Map baggageItemsWithPropagationTags; + // Trace-level propagation tags (_dd.p.*, including the _dd.p.dm decision-maker) belong only + // on the local root. Local children now share the root's PropagationTags instance, so gate + // the emit on span position; otherwise the trace-level tags would be duplicated onto every + // child span. + final boolean isLocalRoot = getRootSpanContextIfDifferent() == null; if (injectBaggageAsTags) { baggageItemsWithPropagationTags = new HashMap<>(baggageItems); if (w3cBaggage != null) { injectW3CBaggageTags(baggageItemsWithPropagationTags); } - propagationTags.fillTagMap(baggageItemsWithPropagationTags); + if (isLocalRoot) { + propagationTags.fillTagMap(baggageItemsWithPropagationTags); + } } else { - baggageItemsWithPropagationTags = propagationTags.createTagMap(); + baggageItemsWithPropagationTags = + isLocalRoot ? propagationTags.createTagMap() : new HashMap<>(); } consumer.accept( diff --git a/dd-trace-core/src/test/java/datadog/trace/core/PropagationTagsChildSpanTest.java b/dd-trace-core/src/test/java/datadog/trace/core/PropagationTagsChildSpanTest.java new file mode 100644 index 00000000000..184e10c1212 --- /dev/null +++ b/dd-trace-core/src/test/java/datadog/trace/core/PropagationTagsChildSpanTest.java @@ -0,0 +1,157 @@ +package datadog.trace.core; + +import static datadog.trace.api.TracePropagationStyle.DATADOG; +import static org.junit.jupiter.api.Assertions.assertFalse; +import static org.junit.jupiter.api.Assertions.assertTrue; + +import datadog.trace.api.DDTraceId; +import datadog.trace.api.sampling.PrioritySampling; +import datadog.trace.bootstrap.instrumentation.api.AgentSpan; +import datadog.trace.core.propagation.ExtractedContext; +import datadog.trace.core.propagation.PropagationTags; +import java.util.Collections; +import java.util.Map; +import org.junit.jupiter.api.BeforeEach; +import org.junit.jupiter.api.Test; + +/** + * Regression guard for the "local children share the parent's {@link PropagationTags}" optimization + * in {@code CoreTracer.buildSpanContext}: a non-root (local child) span must still carry the + * inbound distributed {@code _dd.p.*} tags when it injects. + * + *

Inbound {@code _dd.p.*} live on the root's {@code PropagationTags} (inherited from the {@link + * ExtractedContext}), and reads route to the root via {@code DDSpanContext.getPropagationTags()} — + * so a local child injects the same tags whether it holds its own instance or shares the root's. + * That invariant is what lets the child skip allocating its own {@code empty()} and share the + * root's instead. If {@link #localChildCarriesInboundDdpTags()} regresses, non-root injection is + * dropping inbound {@code _dd.p.*} on every hop. + * + *

Sharing has a second, opposite hazard on the serialization side: trace-level {@code + * _dd.p.*} must be emitted into a span's metadata only on the local root. Since children share the + * root's non-empty instance, {@code DDSpanContext.processTagsAndBaggage} gates the emit on span + * position — otherwise {@code _dd.p.dm} (and friends) would be duplicated onto every child span in + * the chunk, which the {@code test_sampling_span_tags} parametric test forbids. {@link + * #localChildDoesNotEmitTraceLevelDdpTags()} guards that direction. + */ +class PropagationTagsChildSpanTest extends DDCoreJavaSpecification { + + private static final String INBOUND_HEADER = "_dd.p.dm=934086a686-4,_dd.p.anytag=value"; + private static final String INBOUND_TAG = "_dd.p.anytag=value"; + + private CoreTracer tracer; + + @BeforeEach + void setup() { + tracer = tracerBuilder().build(); + } + + private static ExtractedContext extractedWithDdpTags() { + return new ExtractedContext( + DDTraceId.ONE, + 2, + PrioritySampling.SAMPLER_KEEP, + null, + 0, + Collections.emptyMap(), + Collections.emptyMap(), + null, + PropagationTags.factory() + .fromHeaderValue(PropagationTags.HeaderType.DATADOG, INBOUND_HEADER), + null, + DATADOG); + } + + /** What the Datadog codec would inject for {@code x-datadog-tags} from this span. */ + private static String injectedDdpHeader(AgentSpan span) { + return ((DDSpanContext) span.spanContext()) + .getPropagationTags() + .headerValue(PropagationTags.HeaderType.DATADOG); + } + + /** Baseline: the root span (built directly from the extracted context) carries inbound tags. */ + @Test + void rootSpanCarriesInboundDdpTags() { + AgentSpan root = tracer.buildSpan("test", "root").asChildOf(extractedWithDdpTags()).start(); + try { + String header = injectedDdpHeader(root); + assertTrue( + header != null && header.contains(INBOUND_TAG), + "root injected _dd.p.* header should contain inbound tag; was: " + header); + } finally { + root.finish(); + } + } + + /** + * THE open question: a local child of the root. Inbound {@code _dd.p.*} must survive injection + * from the child, or downstream services lose the distributed tags on every non-root hop. + */ + @Test + void localChildCarriesInboundDdpTags() { + AgentSpan root = tracer.buildSpan("test", "root").asChildOf(extractedWithDdpTags()).start(); + AgentSpan child = tracer.buildSpan("test", "child").asChildOf(root.spanContext()).start(); + try { + String header = injectedDdpHeader(child); + assertTrue( + header != null && header.contains(INBOUND_TAG), + "local child injected _dd.p.* header should contain inbound tag; was: " + header); + } finally { + child.finish(); + root.finish(); + } + } + + /** The trace-level {@code _dd.p.*} a span would emit into its serialized metadata (baggage). */ + private static Map emittedPropagationTags(AgentSpan span) { + CapturingConsumer consumer = new CapturingConsumer(); + ((DDSpan) span).processTagsAndBaggage(consumer); + return consumer.metadata.getBaggage(); + } + + /** Serialization baseline: the local root emits the trace-level decision-maker tag. */ + @Test + void rootSpanEmitsDecisionMakerTag() { + AgentSpan root = tracer.buildSpan("test", "root").asChildOf(extractedWithDdpTags()).start(); + try { + Map emitted = emittedPropagationTags(root); + assertTrue( + emitted.containsKey("_dd.p.dm"), + "root serialized metadata should carry _dd.p.dm; was: " + emitted); + } finally { + root.finish(); + } + } + + /** + * Regression guard for the {@code test_sampling_span_tags} parametric test: a non-root (local + * child) span must not emit trace-level {@code _dd.p.*} into its serialized metadata. Because the + * child shares the root's {@link PropagationTags}, an ungated emit duplicates {@code _dd.p.dm} + * onto every child span in the chunk. + */ + @Test + void localChildDoesNotEmitTraceLevelDdpTags() { + AgentSpan root = tracer.buildSpan("test", "root").asChildOf(extractedWithDdpTags()).start(); + AgentSpan child = tracer.buildSpan("test", "child").asChildOf(root.spanContext()).start(); + try { + Map emitted = emittedPropagationTags(child); + assertFalse( + emitted.containsKey("_dd.p.dm"), + "local child serialized metadata must not carry trace-level _dd.p.dm; was: " + emitted); + assertFalse( + emitted.containsKey("_dd.p.anytag"), + "local child serialized metadata must not carry trace-level _dd.p.*; was: " + emitted); + } finally { + child.finish(); + root.finish(); + } + } + + private static final class CapturingConsumer implements MetadataConsumer { + private Metadata metadata; + + @Override + public void accept(Metadata metadata) { + this.metadata = metadata; + } + } +}