Fix attributes override in Rate Limited Sampler

sdk/monitor/azure-monitor-opentelemetry-exporter/CHANGELOG.md

@@ -9,6 +9,8 @@
 ### Breaking Changes
 
 ### Bugs Fixed
+- Fix attributes override in Rate Limited Sampler
+  ([#45592](https://github.com/Azure/azure-sdk-for-python/pull/45592))
 - Add environment variable to disable/enable custom properties truncation
   ([#45479](https://github.com/Azure/azure-sdk-for-python/pull/45479))
 - Fix io counters import issue in performance counters

sdk/monitor/azure-monitor-opentelemetry-exporter/azure/monitor/opentelemetry/exporter/export/trace/_rate_limited_sampling.py

@@ -109,10 +109,8 @@ def should_sample(
         else:
             decision = Decision.DROP
 
-        if sampling_percentage == 100.0:
-            new_attributes = {}
-        else:
-            new_attributes = {} if attributes is None else dict(attributes)
+        new_attributes = {} if attributes is None else dict(attributes)
+        if sampling_percentage != 100.0:
             new_attributes[_SAMPLE_RATE_KEY] = sampling_percentage
 
         return SamplingResult(

sdk/monitor/azure-monitor-opentelemetry-exporter/tests/trace/test_rate_limited_sampling.py

@@ -224,6 +224,39 @@ def test_sampling_attributes(self):
                 self.assertGreaterEqual(float(sample_rate), 0.0)
                 self.assertLessEqual(float(sample_rate), 100.0)
 
+    def test_sampling_percentage_100_does_not_add_sample_rate_attribute(self):
+        sampler = RateLimitedSampler(25.0)
+
+        sampler._sampling_percentage_generator.get = Mock(return_value=100.0)
+
+        original_attributes = {"service.name": "test-service", "operation.name": "test-operation"}
+        result = sampler.should_sample(
+            parent_context=None, trace_id=123, name="test-span", attributes=original_attributes
+        )
+
+        self.assertEqual(dict(result.attributes), original_attributes)
+        self.assertNotIn(_SAMPLE_RATE_KEY, result.attributes)
+        self.assertNotIn(_SAMPLE_RATE_KEY, original_attributes)
+
+        result_none = sampler.should_sample(parent_context=None, trace_id=124, name="test-span", attributes=None)
+        self.assertEqual(dict(result_none.attributes), {})
+        self.assertNotIn(_SAMPLE_RATE_KEY, result_none.attributes)
+
+    def test_sampling_percentage_non_100_adds_sample_rate_attribute(self):
+        sampler = RateLimitedSampler(25.0)
+
+        sampler._sampling_percentage_generator.get = Mock(return_value=42.0)
+
+        original_attributes = {"service.name": "test-service", "operation.name": "test-operation"}
+        result = sampler.should_sample(
+            parent_context=None, trace_id=123, name="test-span", attributes=original_attributes
+        )
+
+        self.assertEqual(dict(result.attributes), {**original_attributes, _SAMPLE_RATE_KEY: 42.0})
+        self.assertIn(_SAMPLE_RATE_KEY, result.attributes)
+        self.assertEqual(result.attributes[_SAMPLE_RATE_KEY], 42.0)
+        self.assertNotIn(_SAMPLE_RATE_KEY, original_attributes)
+
     # Test sampling behavior with edge case trace ID values
     def test_sampler_with_extreme_trace_ids(self):
         sampler = RateLimitedSampler(1.0)