Update trace sampling formula (#8734)

genesor · web-flow · commit 2dd1774ce6eb · 2025-04-28T10:22:58.000+02:00
diff --git a/dd-trace-core/src/main/java/datadog/trace/common/sampling/DeterministicSampler.java b/dd-trace-core/src/main/java/datadog/trace/common/sampling/DeterministicSampler.java
@@ -49,7 +49,7 @@ public DeterministicSampler(final double rate) {
   @Override
   public <T extends CoreSpan<T>> boolean sample(final T span) {
     // unsigned 64 bit comparison with cutoff/threshold
-    return getSamplingId(span) * KNUTH_FACTOR + Long.MIN_VALUE < threshold;
+    return getSamplingId(span) * KNUTH_FACTOR + Long.MIN_VALUE <= threshold;
   }
 
   protected abstract <T extends CoreSpan<T>> long getSamplingId(T span);
diff --git a/dd-trace-core/src/test/groovy/datadog/trace/common/sampling/DeterministicTraceSamplerTest.groovy b/dd-trace-core/src/test/groovy/datadog/trace/common/sampling/DeterministicTraceSamplerTest.groovy
@@ -121,6 +121,7 @@ class DeterministicTraceSamplerTest extends DDSpecification {
     true     | "9828766684487745566"
     true     | "9908585559158765387"
     true     | "9956202364908137547"
+    true     | "9223372036854775808"
   }
 
   def "test sampling none: #traceId"() {

Original file line number	Diff line number	Diff line change
`@@ -49,7 +49,7 @@ public DeterministicSampler(final double rate) {`
`49`	`49`	`@Override`
`50`	`50`	`public <T extends CoreSpan<T>> boolean sample(final T span) {`
`51`	`51`	`// unsigned 64 bit comparison with cutoff/threshold`
`52`		`- return getSamplingId(span) * KNUTH_FACTOR + Long.MIN_VALUE < threshold;`
	`52`	`+ return getSamplingId(span) * KNUTH_FACTOR + Long.MIN_VALUE <= threshold;`
`53`	`53`	`}`
`54`	`54`
`55`	`55`	`protected abstract <T extends CoreSpan<T>> long getSamplingId(T span);`
Original file line number	Diff line number	Diff line change
`@@ -121,6 +121,7 @@ class DeterministicTraceSamplerTest extends DDSpecification {`
`121`	`121`	`true \| "9828766684487745566"`
`122`	`122`	`true \| "9908585559158765387"`
`123`	`123`	`true \| "9956202364908137547"`
	`124`	`+ true \| "9223372036854775808"`
`124`	`125`	`}`
`125`	`126`
`126`	`127`	`def "test sampling none: #traceId"() {`