How can I merge FAISS index chunks while also generating a corresponding .pkl metadata file?

Below is a revised version of your code. In this version:

• We create the output directory (if needed) once before writing files.
• We write the merged FAISS index using faiss.write_index (or save_local if available)
• We then write a corresponding metadata file using pickle.

Make sure that:

– Your output path ends with the extension “.faiss” so that the replacement (to “.pkl”) works correctly.
– You have write permissions in the output directory.

Below is the updated code:

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import faiss
import os
import pickle

def merge_faiss_indexes(index_dir, output_path):
    # Find subdirectories
    subdirs = [
        os.path.join(index_dir, d)
        for d in os.listdir(index_dir)
        if os.path.isdir(os.path.join(index_dir, d))
    ]
    print("Subdirectories found:", subdirs)

    # Collect all .faiss index files from subdirectories
    index_files = []
    for subdir in subdirs:
        for file in os.listdir(subdir):
            if file.endswith('.faiss'):
                index_files.append(os.path.join(subdir, file))

    if not index_files:
        raise ValueError("No FAISS index files found in the directory or subdirectories!")

    print(f"Found FAISS index files: {index_files}")

    # Load the first index as the base index
    base_index = faiss.read_index(index_files[0])
    print(f"Loaded base index: {index_files[0]}")

    # Merge the other indexes into the base index
    for index_file in index_files[1:]:
        print(f"Merging index: {index_file}")
        to_merge = faiss.read_index(index_file)
        base_index.merge_from(to_merge)

    # Ensure that the output directory exists
    output_dir = os.path.dirname(output_path)
    os.makedirs(output_dir, exist_ok=True)

    # Write the merged index.
    # If you want to experiment with save_local instead, check if your index provides that method.
    # For example: base_index.save_local(output_path) rather than faiss.write_index(base_index, output_path)
    faiss.write_index(base_index, output_path)
    print(f"Merged index saved to: {output_path}")

    # Save a metadata file as a .pkl file
    metadata = {
        'description': 'Merged FAISS index',
        'num_indexes': len(index_files)
    }
    # This will change the extension from .faiss to .pkl
    metadata_path = output_path.replace('.faiss', '.pkl')
    with open(metadata_path, 'wb') as pkl_file:
        pickle.dump(metadata, pkl_file)
    print(f"Metadata saved to: {metadata_path}")

if __name__ == "__main__":
    index_dir = "./FAISS_ALL_REF"
    output_path = "./FAISS_MERGED/merged_index.faiss"
    merge_faiss_indexes(index_dir, output_path)

Notes

1. Using save_local:
   If you prefer using a method like save_local instead of write_index (and your FAISS index supports it), simply replace

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   faiss.write_index(base_index, output_path)

   with

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   base_index.save_local(output_path)

   Be sure that the index type you are working with implements that method.

2. File Extensions:
   The replacement for the metadata file works correctly only if the output_path ends with “.faiss”.
   For example, "merged_index.faiss" becomes "merged_index.pkl". Adjust the code if you wish to use a different naming scheme.

This updated code should create both the merged .faiss index file and the associated .pkl metadata file.