From fa8ffa913948ee3bc72b32880358c6d4360bdcec Mon Sep 17 00:00:00 2001
From: Benjamin De Bernardi <benjamin.debernardi@datadoghq.com>
Date: Fri, 25 Apr 2025 10:50:49 +0200
Subject: [PATCH] Update trace sampling formula

---
 .../datadog/trace/common/sampling/DeterministicSampler.java     | 2 +-
 .../trace/common/sampling/DeterministicTraceSamplerTest.groovy  | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

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
index 1e14230528d..c1da7cf25d5 100644
--- 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
index e684a1872fa..daa8240cd92 100644
--- 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"() {