Lightning-AI / Lightning-AI/pytorch-lightning
Distributed mode overwrites the user's choice for dataloaders shuffling
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Description
## 🐛 Bug
I ordered my training data in a specific manner and passed it to the DataLoader with `shuffle=False` (I use `reload_dataloaders_every_n_epochs=1` to control it every epoch). Then, I found out that running in distributed mode re-creates the train dataloader and always set `shuffle=True`. The opposite happens for the val dataloader.
I think that the re-creation of the dataloaders must be using the same shuffle setting the original dataloaders had.
Is there any reason not to do so?
---
Here is the related code with the hard-coded shuffle values:
train - shuffle forced to be true
https://github.com/PyTorchLightning/pytorch-lightning/blob/c33df2639f19d49c5e7520294e3221efe402d684/pytorch_lightning/trainer/data_loading.py#L330-L333
val - shuffle forced to be true
https://github.com/PyTorchLightning/pytorch-lightning/blob/c33df2639f19d49c5e7520294e3221efe402d684/pytorch_lightning/trainer/data_loading.py#L442-L443
cc @borda @justusschock @awaelchli
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Research direction
Start in pytorch_lightning/trainer/data_loading.py at the linked train-loader lines 330-333 and validation-loader lines 442-443. Trace how distributed mode recreates each DataLoader and preserve the original shuffle choices for both loaders. Done means user-specified train and validation shuffling remains unchanged in distributed mode, with the relevant dataloader tests passing.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python, pytorch
- Domain
- distributed-systems, machine-learning
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 48/100