HuggingFace not using specified `cache_dir`

[deependujha]

🐛 Bug

To Reproduce

• Run the below code, and you may observe that my_cache dir is not being used

import litdata as ld

# Define the Hugging Face dataset URI
hf_dataset_uri = "hf://datasets/leonardPKU/clevr_cogen_a_train/data"

# Create a streaming dataset
# dataset is of 13.2 GB - so at the end of the streaming, cache should be clear
dataset = ld.StreamingDataset(hf_dataset_uri, cache_dir = "my_cache", max_cache_size="10GB")

# Stream the dataset using StreamingDataLoader
dataloader = ld.StreamingDataLoader(dataset, batch_size=4)
for sample in dataloader:
    pass 

Expected behavior

Additional context

Environment detail

• PyTorch Version (e.g., 1.0):
• OS (e.g., Linux):
• How you installed PyTorch (conda, pip, source):
• Build command you used (if compiling from source):
• Python version:
• CUDA/cuDNN version:
• GPU models and configuration:
• Any other relevant information:

[philgzl]

I am facing the same issue.

Isn't it because of these two lines?

litData/src/litdata/streaming/dataset.py

Lines 110 to 111 in cb3fc81

	cache_dir.path = index_path
	input_dir.path = index_path

• The first line negates the user-provided cache_dir
• The second line also has to be removed, else _try_create_cache_dir is not called in subsample_streaming_dataset and input_dir.path is used as the cache dir.

I wanted to open a PR but idk how strict the discuss-in-issue-before-submitting rule is.

[deependujha]

Hi @philgzl , feel free to open a PR.

[bhimrazy]

One of the changes that would be added after #560 is that:

Previously, all chunks were also stored in .cache/litdata-cache-index-pq.

This directory was originally used to download and store chunks during the indexing process before actual streaming, which is no longer the case.

Now, the chunks are stored in the DEFAULT_CACHE_DIR, as is typical for LitData-optimized chunks — which is a nice improvement.

Given that, I don’t see a reason for keeping the .cache/litdata-cache-index-pq directory anymore. Would it make sense to consolidate everything under DEFAULT_CACHE_DIR? Otherwise, we’d be maintaining two separate directories — one for storing the index and another for copying the index file and storing chunks.

In case a user wants to store the index file separately, they can run index_hf_dataset first by passing a cache_dir, and then pass that path as the index_path to StreamingDataset.

Otherwise, the index can simply be stored in the DEFAULT_CACHE_DIR or user passed cache_dir in StreamingDataset along with the chunks.

What do you all think?
cc: @tchaton @deependujha @philgzl

[philgzl]

I agree.