.. _unnecessary-ray-get: Anti-pattern: Calling ray.get unnecessarily harms performance ============================================================= **TLDR:** Avoid calling :func:`ray.get() ` unnecessarily for intermediate steps. Work with object references directly, and only call ``ray.get()`` at the end to get the final result. When ``ray.get()`` is called, objects must be transferred to the worker/node that calls ``ray.get()``. If you don't need to manipulate the object, you probably don't need to call ``ray.get()`` on it! Typically, it’s best practice to wait as long as possible before calling ``ray.get()``, or even design your program to avoid having to call ``ray.get()`` at all. Code example ------------ **Anti-pattern:** .. literalinclude:: ../doc_code/anti_pattern_unnecessary_ray_get.py :language: python :start-after: __anti_pattern_start__ :end-before: __anti_pattern_end__ .. figure:: ../images/unnecessary-ray-get-anti.svg **Better approach:** .. literalinclude:: ../doc_code/anti_pattern_unnecessary_ray_get.py :language: python :start-after: __better_approach_start__ :end-before: __better_approach_end__ .. figure:: ../images/unnecessary-ray-get-better.svg Notice in the anti-pattern example, we call ``ray.get()`` which forces us to transfer the large rollout to the driver, then again to the *reduce* worker. In the fixed version, we only pass the reference to the object to the *reduce* task. The ``reduce`` worker will implicitly call ``ray.get()`` to fetch the actual rollout data directly from the ``generate_rollout`` worker, avoiding the extra copy to the driver. Other ``ray.get()`` related anti-patterns are: - :doc:`ray-get-loop` - :doc:`ray-get-submission-order`