perf(rc): avoid calling config subscribers on duplicate values

ddtrace/settings/_config.py

@@ -322,6 +322,18 @@ def set_value_source(self, value: Any, source: _ConfigSource) -> None:
         else:
             log.warning("Invalid source: %s", source)
 
+    def get_value_source(self, source: _ConfigSource) -> _JSONType:
+        if source == "code":
+            return self._code_value
+        elif source == "remote_config":
+            return self._rc_value
+        elif source == "env_var":
+            return self._env_value
+        elif source == "default":
+            return self._default_value
+        else:
+            log.warning("Invalid source: %s", source)
+
     def set_code(self, value: _JSONType) -> None:
         self._code_value = value
 
@@ -790,8 +802,11 @@ def _set_config_items(self, items):
         # type: (List[Tuple[str, Any, _ConfigSource]]) -> None
         item_names = []
         for key, value, origin in items:
-            item_names.append(key)
             item = self._config[key]
+            if item.get_value_source(origin) == value:
+                # No change in config value, no need to notify subscribers or report telemetry
+                continue
+            item_names.append(key)
             item.set_value_source(value, origin)
             telemetry_writer.add_configuration(item._name, item.value(), item.source())
         self._notify_subscribers(item_names)

tests/internal/test_settings.py

@@ -638,3 +638,37 @@ def test_config_public_properties_and_methods():
         "tags",
         "version",
     }, public_attrs
+
+
+@pytest.mark.subprocess()
+def test_subscription_handler_called_once_for_duplicate_values():
+    """This test ensures that the subscription handler is called only once
+    when the value is set multiple times to the same value.
+    It also checks that the handler is called again when the value changes.
+    """
+    from ddtrace import config
+
+    call_count = 0
+
+    def _handler(cfg, items):
+        global call_count
+        call_count += 1
+
+    config._subscribe(
+        [
+            "_logs_injection",
+        ],
+        _handler,
+    )
+
+    assert call_count == 0, "Handler should not be called before setting the value"
+    for _ in range(3):
+        config._logs_injection = "true"
+        assert call_count == 1, "Handler should be called only once for the same value"
+
+    for _ in range(3):
+        config._logs_injection = "false"
+        assert call_count == 2, "Handler should be called only once for the same value"
+
+    config._logs_injection = "true"
+    assert call_count == 3, "Handler should be called again for a different value"