[Serve] Eliminate per-replica-per-tick Pydantic rebuild in update_act…

python/ray/serve/_private/deployment_state.py

@@ -1473,10 +1473,23 @@ def update_state(self, state: ReplicaState) -> None:
         """Updates state in actor details."""
         self.update_actor_details(state=state)
 
+    _SENTINEL = object()
+
     def update_actor_details(self, **kwargs) -> None:
-        details_kwargs = self._actor_details.dict()
-        details_kwargs.update(kwargs)
-        self._actor_details = ReplicaDetails(**details_kwargs)
+        # Fast path: skip if all provided values are already current.
+        # This avoids unnecessary object creation on every tick when the
+        # pop-iterate-readd pattern re-adds replicas without state changes.
+        # We use _SENTINEL (not None) as the getattr default so that an
+        # invalid field name always fails the check and falls through to
+        # .copy(), which will raise an appropriate error.
+        if all(
+            getattr(self._actor_details, k, self._SENTINEL) == v
+            for k, v in kwargs.items()
+        ):
+            return
+        # Use .copy(update=...) instead of .dict() + reconstruction to avoid
+        # full Pydantic serialization and validation on every update.
+        self._actor_details = self._actor_details.copy(update=kwargs)
 
     def resource_requirements(self) -> Tuple[str, str]:
         """Returns required and currently available resources.