Lightning-AI / Lightning-AI/pytorch-lightning

Refactor distributed_sampler update in `data_connector.py` for distributed strategy

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data handling priority: 2 refactor strategy
Dominant language
Python
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Description

## Proposed refactor

This issue follows @ananthsub 's https://github.com/PyTorchLightning/pytorch-lightning/issues/11756 to move strategy-specific dataloader logic to the stategies.

### Motivation

`_prepare_dataloader()` function in `data_connector.py` handles the logic whether the dataloader needs to update the distributed sampler when user is using distributed strategy (see the following code link)
https://github.com/PyTorchLightning/pytorch-lightning/blob/cc43d07db1ab77385feff04c01f040c5cad805a9/pytorch_lightning/trainer/connectors/data_connector.py#L360-L372

However, modifying sampler in dataloader can be pushed directly to strategy class. Similar to issue #12216 , we can move the logic to `Strategy` base class. For any strategy classes have `is_distributed=True` flag, they can verify if the dataloader need to update the sampler.

### Pitch

We can move the logic to `Strategy` base class. For any strategy classes have `is_distributed=True` flag, they can verify if the dataloader need to update the sampler.

### Additional context
cc: @edward-io @four4fish @ananthsub

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cc @justusschock @awaelchli @rohitgr7 @ninginthecloud @otaj @tchaton @akihironitta @carmocca

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with _prepare_dataloader() in pytorch_lightning/trainer/connectors/data_connector.py, especially the linked sampler-update section, then read the Strategy base class and issue #12216 for the related direction. The work is done when the distributed-sampler decision is handled by the appropriate strategy classes while preserving the existing dataloader behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
python, pytorch
Domain
distributed-systems, machine-learning
Issue type
Refactor
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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