Why are there so many indexes for the MIRACL-Korean index?

[steven-channel]

I'm running the command for evaluating the mDPR model on the MIRACL-Korean benchmark provided here: https://castorini.github.io/pyserini/2cr/miracl.html

The command is:

python -m pyserini.search.faiss \
  --threads 16 --batch-size 512 \
  --encoder-class auto \
  --encoder castorini/mdpr-tied-pft-msmarco-ft-miracl-ko \
  --topics miracl-v1.0-ko-dev \
  --index miracl-v1.0-ko-mdpr-tied-pft-msmarco-ft-miracl-ko \
  --output run.miracl.mdpr-tied-pft-msmarco-ft-miracl.ko.dev.txt --hits 1000

As far as I know, the number of documents (i.e., positive and negative passages) in the MIRACL-Korean dev set is 3,057 with some duplicates. However, I'm noticing that the number of documents contained in the index is 1,486,752. Why are there so many?