wehub-resource-sync
42 lines
1.7 KiB
ReStructuredText
42 lines
1.7 KiB
ReStructuredText
.. _unnecessary-ray-get:
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Anti-pattern: Calling ray.get unnecessarily harms performance
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=============================================================
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**TLDR:** Avoid calling :func:`ray.get() <ray.get>` unnecessarily for intermediate steps. Work with object references directly, and only call ``ray.get()`` at the end to get the final result.
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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!
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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.
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Code example
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------------
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**Anti-pattern:**
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.. literalinclude:: ../doc_code/anti_pattern_unnecessary_ray_get.py
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:language: python
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:start-after: __anti_pattern_start__
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:end-before: __anti_pattern_end__
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.. figure:: ../images/unnecessary-ray-get-anti.svg
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**Better approach:**
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.. literalinclude:: ../doc_code/anti_pattern_unnecessary_ray_get.py
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:language: python
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:start-after: __better_approach_start__
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:end-before: __better_approach_end__
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.. figure:: ../images/unnecessary-ray-get-better.svg
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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.
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In the fixed version, we only pass the reference to the object to the *reduce* task.
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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.
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Other ``ray.get()`` related anti-patterns are:
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- :doc:`ray-get-loop`
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- :doc:`ray-get-submission-order`
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