COIL

Repo for our NAACL paper, COIL: Revisit Exact Lexical Match in Information Retrieval with Contextualized Inverted List. The code covers learning COIL models well as encoding and retrieving with COIL index.

The code was refactored from our original experiment version to use the huggingface Trainer interface for future compatibility.

Contextualized Exact Lexical Match

COIL systems are based on the idea of contextualized exact lexical match. It replaces term frequency based term matching in classical systems like BM25 with contextualized word representation similarities. It thereby gains the ability to model matching of context. Meanwhile COIL confines itself to comparing exact lexical matched tokens and therefore can retrieve efficiently with inverted list form data structure. Details can be found in our paper.

Dependencies

The code has been tested with,

pytorch==1.8.1
transformers==4.2.1
datasets==1.1.3

To use the retriever, you need in addition,

torch_scatter==2.0.6
faiss==1.7.0

Resource

MSMARCO Passage Ranking

Here we present two systems: one uses hard negatives (HN) and the other does not. COIL w/o HN is trained with BM25 negatives, and COIL w/ HN is trained in addition with hard negatives mined with another trained COIL.

• Right Click to Download.
• The COIL w/o HN model was a rerun as we lost the original checkpoint. There's a slight difference in dev performance, about 0.5% and also some improvement on the DL2019 test.

Tokenized data and model checkpoint link

Hard negative data and model checkpoint link

more to be added soon

Usage

The following sections will work through how to use this code base to train and retrieve over the MSMARCO passage ranking data set.

Training

You can download the train file psg-train.tar.gz for BERT from our resource link. Alternatively, you can run pre-processing by yourself following the pre-processing instructions.

Extract the training set from the tar ball and run the following code to launch training for msmarco passage.

python run_marco.py \  
  --output_dir $OUTDIR \  
  --model_name_or_path bert-base-uncased \  
  --do_train \  
  --save_steps 4000 \  
  --train_dir /path/to/psg-train \  
  --q_max_len 16 \  
  --p_max_len 128 \  
  --fp16 \  
  --per_device_train_batch_size 8 \  
  --train_group_size 8 \  
  --cls_dim 768 \  
  --token_dim 32 \  
  --warmup_ratio 0.1 \  
  --learning_rate 5e-6 \  
  --num_train_epochs 5 \  
  --overwrite_output_dir \  
  --dataloader_num_workers 16 \  
  --no_sep \  
  --pooling max 

Encoding

After training, you can encode the corpus splits and queries.

You can download pre-processed data for BERT, corpus.tar.gz, queries.{dev, eval}.small.json here.

for i in $(seq -f "%02g" 0 99)  
do  
  mkdir ${ENCODE_OUT_DIR}/split${i}  
  python run_marco.py \  
    --output_dir $ENCODE_OUT_DIR \  
    --model_name_or_path $CKPT_DIR \  
    --tokenizer_name bert-base-uncased \  
    --cls_dim 768 \  
    --token_dim 32 \  
    --do_encode \  
    --no_sep \  
    --p_max_len 128 \  
    --pooling max \  
    --fp16 \  
    --per_device_eval_batch_size 128 \  
    --dataloader_num_workers 12 \  
    --encode_in_path ${TOKENIZED_DIR}/split${i} \  
    --encoded_save_path ${ENCODE_OUT_DIR}/split${i}
done

If on a cluster, the encoding loop can be paralellized. For example, say if you are on a SLURM cluster, use srun,

for i in $(seq -f "%02g" 0 99)  
do  
  mkdir ${ENCODE_OUT_DIR}/split${i}  
  srun --ntasks=1 -c4 --mem=16000 -t0 --gres=gpu:1 python run_marco.py \  
    --output_dir $ENCODE_OUT_DIR \  
    --model_name_or_path $CKPT_DIR \  
    --tokenizer_name bert-base-uncased \  
    --cls_dim 768 \  
    --token_dim 32 \  
    --do_encode \  
    --no_sep \  
    --p_max_len 128 \  
    --pooling max \  
    --fp16 \  
    --per_device_eval_batch_size 128 \  
    --dataloader_num_workers 12 \  
    --encode_in_path ${TOKENIZED_DIR}/split${i} \  
    --encoded_save_path ${ENCODE_OUT_DIR}/split${i}&
done

Then encode the queries,

python run_marco.py \  
  --output_dir $ENCODE_QRY_OUT_DIR \  
  --model_name_or_path $CKPT_DIR \  
  --tokenizer_name bert-base-uncased \  
  --cls_dim 768 \  
  --token_dim 32 \  
  --do_encode \  
  --p_max_len 16 \  
  --fp16 \  
  --no_sep \  
  --pooling max \  
  --per_device_eval_batch_size 128 \  
  --dataloader_num_workers 12 \  
  --encode_in_path $TOKENIZED_QRY_PATH \  
  --encoded_save_path $ENCODE_QRY_OUT_DIR

Note that here p_max_len always controls the maximum length of the encoded text, regardless of the input type.

Retrieval

To do retrieval, run the following steps,

(Note that there is no dependency in the for loop within each step, meaning that if you are on a cluster, you can distribute the jobs across nodes using srun or qsub.)

1. build document index shards

for i in $(seq 0 9)  
do  
 python retriever/sharding.py \  
   --n_shards 10 \  
   --shard_id $i \  
   --dir $ENCODE_OUT_DIR \  
   --save_to $INDEX_DIR \  
   --use_torch
done  

2. reformat encoded query

python retriever/format_query.py \  
  --dir $ENCODE_QRY_OUT_DIR \  
  --save_to $QUERY_DIR \  
  --as_torch

3. retrieve from each shard

for i in $(seq -f "%02g" 0 9)  
do  
  python retriever/retriever-compat.py \  
      --query $QUERY_DIR \  
      --doc_shard $INDEX_DIR/shard_${i} \  
      --top 1000 \  
      --save_to ${SCORE_DIR}/intermediate/shard_${i}.pt
done 

4. merge scores from all shards

python retriever/merger.py \  
  --score_dir ${SCORE_DIR}/intermediate/ \  
  --query_lookup  ${QUERY_DIR}/cls_ex_ids.pt \  
  --depth 1000 \  
  --save_ranking_to ${SCORE_DIR}/rank.txt

python data_helpers/msmarco-passage/score_to_marco.py \  
  --score_file ${SCORE_DIR}/rank.txt

Note that this compat(ible) version of retriever differs from our internal retriever. It relies on torch_scatter package for scatter operation so that we can have a pure python code that can easily work across platforms. We do notice that on our system torch_scatter does not scale very well with number of cores. We may in the future release another faster version of retriever that requires some compiling work.

Data Format

For both training and encoding, the core code expects pre-tokenized data.

Training Data

Training data is grouped by query into one or several json files where each line has a query, its corresponding positives and negatives.

{
    "qry": {
        "qid": str,
        "query": List[int],
    },
    "pos": List[
        {
            "pid": str,
            "passage": List[int],
        }
    ],
    "neg": List[
        {
            "pid": str,
            "passage": List[int]
        }
    ]
}

Encoding Data

Encoding data is also formatted into one or several json files. Each line corresponds to an entry item.

{"pid": str, "psg": List[int]}

Note that for code simplicity, we share this format for query/passage/document encoding.