[GitHub] [beam] damccorm opened a new issue, #20900: Add support for out-of-band pickling (pickle 5) in PickleCoder

[GitBox <gi...@apache.org>]

damccorm opened a new issue, #20900:
URL: https://github.com/apache/beam/issues/20900

   dev@ discussion: https://lists.apache.org/thread.html/r266f37640901544927205b913d4903340d6c59c3d94905e5dda0db42%40%3Cdev.beam.apache.org%3E
   
   PickleCoder should support out-of-band pickling to avoid unnecessary memory copies for types that support it (including numpy and pandas types).
   
   Imported from Jira [BEAM-12418](https://issues.apache.org/jira/browse/BEAM-12418). Original Jira may contain additional context.
   Reported by: bhulette.


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[GitHub] [beam] TheNeuralBit commented on issue #20900: Add support for out-of-band pickling (pickle 5) in PickleCoder

[GitBox <gi...@apache.org>]

TheNeuralBit commented on issue #20900:
URL: https://github.com/apache/beam/issues/20900#issuecomment-1251658001

   I looked into this a little bit. I don't think we can see huge performance wins here because we don't have an out-of-band path for transferring the data (e.g. shared memory). No matter what we're going to need to write/read the buffers over the Fn API in-band with the rest of the encoded object.
   
   _However_ [as noted in PEP 574](https://peps.python.org/pep-0574/#improved-in-band-performance) one can still see an improvement in in-band performance with the pickle 5 protocol. It can eliminate a memcopy on the serialization path because we no longer have to materialize a full byte[] representing the serialized object (copying all the buffers) and then copy that byte[] to the output buffer.
   
   I ran some benchmarks to confirm this, we can see that with pickle5, pickle.dump performs better when writing to a file-like object:
   ![image](https://user-images.githubusercontent.com/675055/191133887-f97f35ce-206c-4adc-90c6-d49b30c2401f.png)
   
   To take advantage of this I think we'd need to expose the OutputStream as a file-like object, and pass that to pickle.dump. This would allow pickle to write buffers directly to the output stream. Note the current behavior is to execute `pickle.dumps` (one memcopy) and write the result to the output stream (second memcopy).
   
   CCing a few folks:
   @robertwb @shoyer @tvalentyn @apilloud 


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