What is model checkpointing?

Model checkpointing is a technique used during machine learning training to save the current state of a model at specific intervals. This includes the model’s architecture, weights, optimizer state, and other variables necessary to resume training or deploy the model later. The primary purpose is to prevent loss of progress due to interruptions like hardware failures, software crashes, or manual stops. By saving snapshots of the model, developers can restart training from the last saved checkpoint instead of beginning from scratch, saving time and computational resources. Checkpointing also enables tracking model performance over time, making it easier to compare versions or revert to a better-performing state.

For example, frameworks like TensorFlow and PyTorch provide built-in tools for checkpointing. In TensorFlow, the tf.keras.callbacks.ModelCheckpoint callback saves the model after every epoch or when a metric (like validation loss) improves. PyTorch uses torch.save() to serialize the model and optimizer states into a file. A common practice is to save checkpoints at regular intervals (e.g., every 10 epochs) and retain the best-performing version based on validation metrics. This is particularly useful when training large models, such as neural networks for image recognition, where a single training run might take days. Without checkpointing, a crash at epoch 99 of a 100-epoch training cycle would force developers to restart entirely.

Checkpointing also supports practical workflows like fine-tuning and experimentation. For instance, a developer might train a model for 50 epochs, then use the best checkpoint to test adjustments to hyperparameters or data preprocessing. In distributed training scenarios, checkpoints ensure synchronization across multiple GPUs or nodes. However, managing checkpoints requires careful planning: saving too frequently wastes storage, while saving too rarely risks losing progress. Developers often automate cleanup by keeping only the most recent checkpoints and the top-performing ones. When deploying, the final model is typically loaded from the checkpoint with the best validation performance, ensuring optimal results. Proper checkpointing balances efficiency, safety, and flexibility in the development lifecycle.