tff.simulation.FileCheckpointManager

A checkpoint manager backed by a file system.

tff.simulation.FileCheckpointManager(
    root_dir: str,
    prefix: str = 'ckpt_',
    step: int = 1,
    keep_total: int = 5,
    keep_first: bool = True
)

This checkpoint manager is a utility to save and load checkpoints. While the checkpoint manager is compatible with any nested structure supported by tf.convert_to_tensor, checkpoints may often represent the output of a tff.templates.IterativeProcess. For example, one possible use case would be to save the ServerState output of an iterative process created via tff.learning. This is comparable to periodically saving model weights and optimizer states during non-federated training.

The implementation you find here is slightly different from tf.train.CheckpointManager. This implementation yields nested structures that are immutable whereas tf.train.CheckpointManager is used to manage tf.train.Checkpoint objects, which are mutable collections. Additionally, this implementation allows retaining the initial checkpoint as part of the total number of checkpoints that are kept.

The checkpoint manager is intended only for allowing simulations to be resumed after interruption. In particular, it is intended to only restart the same simulation, run with the same version of TensorFlow Federated.

Args
root_dir	A path on the filesystem to store checkpoints.
prefix	A string to use as the prefix for checkpoint names.
step	How often the checkpoint manager should save a checkpoint. When calling FileCheckpointManager.save_checkpoint, a checkpoint will only be written for round numbers divisible by step.
keep_total	An integer representing the total number of checkpoints to keep.
keep_first	A boolean indicating if the first checkpoint should be kept, irrespective of whether it is in the last keep_total checkpoints. This is desirable in settings where you would like to ensure full reproducibility of the simulation, especially in settings where model weights or optimizer states are initialized randomly. By loading from the initial checkpoint, one can avoid re-initializing and obtaining different results.

Methods

load_checkpoint

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load_checkpoint(
    structure: Any,
    round_num: int
) -> Any

Returns the checkpointed state for the given round_num.

Args
structure	A nested structure which tf.convert_to_tensor supports to use as a template when reconstructing the loaded template.
round_num	An integer representing the round to load from.

load_latest_checkpoint

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load_latest_checkpoint(
    structure: Any
) -> Tuple[Any, Union[int, None]]

Loads the latest state and round number.

Args
structure	A nested structure which tf.convert_to_tensor supports to use as a template when reconstructing the loaded template.

Returns
A tuple of (state, round_num) where state matches the Python structure in structure, and round_num is an integer. If no checkpoints have been previously saved, returns the tuple (None, None).

load_latest_checkpoint_or_default

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load_latest_checkpoint_or_default(
    default: Any
) -> Tuple[Any, int]

Loads latest checkpoint, loading default if no checkpoints exist.

Saves default as the 0th checkpoint if no checkpoints exist.

Args
default	A nested structure which tf.convert_to_tensor supports to use as a template when reconstructing the loaded template. This structure will be saved as the checkpoint for round number 0 and returned if there are no pre-existing saved checkpoints.

Returns
A tuple of (state, round_num) where state matches the Python structure in structure, and round_num is an integer. If no checkpoints have been written, returns (default, 0).

save_checkpoint

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save_checkpoint(
    state: Any,
    round_num: int
) -> None

Saves a new checkpointed state for the given round_num.

Note that a checkpoint is only written if round_num is divisible by the step initialization argument of the manager.

Args
state	A nested structure which tf.convert_to_tensor supports.
round_num	An integer representing the current training round.