pytorch/docs/source/distributed.checkpoint.rst
Chien-Chin Huang 9d0c3e21d0 [state_dict][9/N] Add get and set APIs for model and optimizer state_dict (#112203)
The original get_state_dict and set_state_dict pair is too complicated because of the possible combinations of usages. This PR adds the APIs to get/set model_state_dict and optimizer_state_dict seperately.

Differential Revision: [D50713584](https://our.internmc.facebook.com/intern/diff/D50713584/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/112203
Approved by: https://github.com/wz337
ghstack dependencies: #112167
2023-11-02 22:03:57 +00:00

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.. role:: hidden
:class: hidden-section
Distributed Checkpoint - torch.distributed.checkpoint
=====================================================
Distributed Checkpoint (DCP) support loading and saving models from multiple ranks in parallel.
It handles load-time resharding which enables saving in one cluster topology and loading into another.
DCP is different than `torch.save` and `torch.load` in a few significant ways:
* It produces multiple files per checkpoint, with at least one per rank.
* It operates in place, meaning that the model should allocate its data first and DCP uses that storage instead.
The entrypoints to load and save a checkpoint are the following:
.. automodule:: torch.distributed.checkpoint
.. currentmodule:: torch.distributed.checkpoint
.. autofunction:: load_state_dict
.. autofunction:: save_state_dict
This `example <https://github.com/pytorch/pytorch/blob/main/torch/distributed/checkpoint/examples/fsdp_checkpoint_example.py>`_ shows how to use Pytorch Distributed Checkpoint to save a FSDP model.
The following types define the IO interface used during checkpoint:
.. autoclass:: torch.distributed.checkpoint.StorageReader
:members:
.. autoclass:: torch.distributed.checkpoint.StorageWriter
:members:
The following types define the planner interface used during checkpoint:
.. autoclass:: torch.distributed.checkpoint.LoadPlanner
:members:
.. autoclass:: torch.distributed.checkpoint.LoadPlan
:members:
.. autoclass:: torch.distributed.checkpoint.ReadItem
:members:
.. autoclass:: torch.distributed.checkpoint.SavePlanner
:members:
.. autoclass:: torch.distributed.checkpoint.SavePlan
:members:
.. autoclass:: torch.distributed.checkpoint.WriteItem
:members:
We provide a filesystem based storage layer:
.. autoclass:: torch.distributed.checkpoint.FileSystemReader
:members:
.. autoclass:: torch.distributed.checkpoint.FileSystemWriter
:members:
We provide default implementations of `LoadPlanner` and `SavePlanner` that
can handle all of torch.distributed constructs such as FSDP, DDP, ShardedTensor and DistributedTensor.
.. autoclass:: torch.distributed.checkpoint.DefaultSavePlanner
:members:
.. autoclass:: torch.distributed.checkpoint.DefaultLoadPlanner
:members:
We provide a set of APIs to help users do get and set state_dict easily. This is
an experimental feature and is subject to change.
.. autofunction:: torch.distributed.checkpoint.state_dict.get_state_dict
.. autofunction:: torch.distributed.checkpoint.state_dict.get_model_state_dict
.. autofunction:: torch.distributed.checkpoint.state_dict.get_optimizer_state_dict
.. autofunction:: torch.distributed.checkpoint.state_dict.set_state_dict
.. autofunction:: torch.distributed.checkpoint.state_dict.set_model_state_dict
.. autofunction:: torch.distributed.checkpoint.state_dict.set_optimizer_state_dict
.. autoclass:: torch.distributed.checkpoint.state_dict.StateDictOptions
:members: