RUM-6870 use deterministic sampling for distributed tracing

DataDog · Dec 16, 2024 · 08baa03 · 08baa03
1 parent d984be1
commit 08baa03
Showing 1 changed file with 9 additions and 2 deletions.
diff --git a/...s/core/src/rum/instrumentation/resourceTracking/distributedTracing/distributedTracing.tsx b/...s/core/src/rum/instrumentation/resourceTracking/distributedTracing/distributedTracing.tsx
@@ -12,6 +12,9 @@ import type { SpanId, TraceId } from './TracingIdentifier';
 import type { Hostname } from './firstPartyHosts';
 import { getPropagatorsForHost } from './firstPartyHosts';
 
+const knuthFactor = BigInt('1111111111111111111')
+const twoPow64 = BigInt('0x10000000000000000') // 2n ** 64n
+
 export type DdRumResourceTracingAttributes =
     | {
           tracingStrategy: 'KEEP';
@@ -62,9 +65,13 @@ const generateTracingAttributesWithSampling = (
     tracingSamplingRate: number,
     propagatorTypes: PropagatorType[]
 ): DdRumResourceTracingAttributes => {
-    const isSampled = Math.random() * 100 <= tracingSamplingRate;
+    const traceId = TracingIdentifier.createTraceId();
+    const hash = (traceId.id * knuthFactor) % twoPow64
+
+    const isSampled  =Number(hash) <= (tracingSamplingRate / 100) * Number(twoPow64)
+
     const tracingAttributes: DdRumResourceTracingAttributes = {
-        traceId: TracingIdentifier.createTraceId(),
+        traceId: traceId,
         spanId: TracingIdentifier.createSpanId(),
         samplingPriorityHeader: isSampled ? '1' : '0',
         tracingStrategy: 'KEEP',