feat(nextjs): Skip OTEL root spans emitted by Next.js (#11623)

We now skip any OTEL spans that Next.js emits, unless we already have a
parent span that was created elsewhere (e.g. by our auto
instrumentation). This way, we should be able to ensure consistent root
spans for all cases.

Author: mydea

packages/opentelemetry/src/sampler.ts

@@ -62,19 +62,14 @@ export class SentrySampler implements Sampler {
       return { decision: SamplingDecision.NOT_RECORD, traceState };
     }
 
-    let parentSampled: boolean | undefined = undefined;
-
-    // Only inherit sample rate if `traceId` is the same
-    // Note for testing: `isSpanContextValid()` checks the format of the traceId/spanId, so we need to pass valid ones
-    if (parentSpan && parentContext && isSpanContextValid(parentContext) && parentContext.traceId === traceId) {
-      if (parentContext.isRemote) {
-        parentSampled = getParentRemoteSampled(parentSpan);
-        DEBUG_BUILD &&
-          logger.log(`[Tracing] Inheriting remote parent's sampled decision for ${spanName}: ${parentSampled}`);
-      } else {
-        parentSampled = getSamplingDecision(parentContext);
-        DEBUG_BUILD && logger.log(`[Tracing] Inheriting parent's sampled decision for ${spanName}: ${parentSampled}`);
-      }
+    const parentSampled = parentSpan ? getParentSampled(parentSpan, traceId, spanName) : undefined;
+
+    // If we encounter a span emitted by Next.js, we do not want to sample it
+    // The reason for this is that the data quality of the spans varies, it is different per version of Next,
+    // and we need to keep our manual instrumentation around for the edge runtime anyhow.
+    // BUT we only do this if we don't have a parent span with a sampling decision yet
+    if (spanAttributes['next.span_type'] && typeof parentSampled !== 'boolean') {
+      return { decision: SamplingDecision.NOT_RECORD, traceState: traceState };
     }
 
     const [sampled, sampleRate] = sampleSpan(options, {
@@ -129,3 +124,24 @@ function getParentRemoteSampled(parentSpan: Span): boolean | undefined {
   // Only inherit sampled if `traceId` is the same
   return traceparentData && traceId === traceparentData.traceId ? traceparentData.sampled : undefined;
 }
+
+function getParentSampled(parentSpan: Span, traceId: string, spanName: string): boolean | undefined {
+  const parentContext = parentSpan.spanContext();
+
+  // Only inherit sample rate if `traceId` is the same
+  // Note for testing: `isSpanContextValid()` checks the format of the traceId/spanId, so we need to pass valid ones
+  if (isSpanContextValid(parentContext) && parentContext.traceId === traceId) {
+    if (parentContext.isRemote) {
+      const parentSampled = getParentRemoteSampled(parentSpan);
+      DEBUG_BUILD &&
+        logger.log(`[Tracing] Inheriting remote parent's sampled decision for ${spanName}: ${parentSampled}`);
+      return parentSampled;
+    }
+
+    const parentSampled = getSamplingDecision(parentContext);
+    DEBUG_BUILD && logger.log(`[Tracing] Inheriting parent's sampled decision for ${spanName}: ${parentSampled}`);
+    return parentSampled;
+  }
+
+  return undefined;
+}