Query Encoder Distillation via Embedding Alignment is a Strong Baseline Method to Boost Dense Retriever Online Efficiency

This repository contains the code for the Query Encoder Distillation paper.

Abstract

In this work, we propose a minimalistic unsupervised baseline method for enhancing the online efficiency of dual encoder (DE) based text dense information retrieval (IR) systems through query encoder embedding-alignment distillation, i.e., simply minimizing the Euclidean distance between the student and teacher query embeddings over query text corpus. We investigate the importance of student initialization, showing that initialization with subset of teacher layers, in particular top and bottom few layers, can improve inference efficiency over 6 times with only 7.5% average performance degradation measured by the BEIR benchmark. Our findings aim to increase neural IR system accessibility and prompt the community to reconsider the trade-offs between method complexity and performance improvements.

Requirements

Please use the following command to install the required packages:

pip install -r requirements.txt

Alternatively, one can leverage conda via:

conda env create -f environment.yml 

Also, one need sufficient GPU RAM to create embedding indexing for some of the large evaluation corpus like HotpotQA.

Usages

One can refer to the Makefile for a simple example workflow that distill and evaluate a two-layer query encoder from msmarco-bert-base-dot-v5. To run the example, type:

make example

Three scripts drives this work. distill.py initializes a student based on one of the two strategies in the paper as specified, and minimize the embedding Euclidean distances over the MS MARCO queries. The output directory should be specified by the user, usually models/<YOUR_MODEL_NAME>/. benchmark.py help download and index BEIR datasets under benchmarks/. Two sub folders benchmarks/raw/ and benchmarks/faiss/ will be created to store the raw corpus and FAISS indexing. It will then evaluate the specified query encoder with common performance metrics like nDCG@k. ispeed.py help evaluate inference throughput on a single CUDA device. All scripts comes with a help page, type:

python <SCRIPT_NAME>.py --help

The implementation is simple and should be straightforward to read or adapt. However, please feel free to email [email protected] for clarification.

Training Data

We use the MS MARCO dataset for model distillation. Specifically, we only used the queries from the training set (and dev set for validation). The distill.py script will automatically download the dataset and save it under the downloads/ folder. There should be a copy of the dataset within this repository as well.

Citing & Authors

If you find this work helpful, feel free to cite our publication submitted to the SustaiNLP workshop at ACL 2023.

@inproceedings{wang-hong-2023-query,
    title = "Query Encoder Distillation via Embedding Alignment is a Strong Baseline Method to Boost Dense Retriever Online Efficiency",
    author = "Wang, Yuxuan  and
      Hong, Lyu",
    editor = "Sadat Moosavi, Nafise  and
      Gurevych, Iryna  and
      Hou, Yufang  and
      Kim, Gyuwan  and
      Kim, Young Jin  and
      Schuster, Tal  and
      Agrawal, Ameeta",
    booktitle = "Proceedings of The Fourth Workshop on Simple and Efficient Natural Language Processing (SustaiNLP)",
    month = jul,
    year = "2023",
    address = "Toronto, Canada (Hybrid)",
    publisher = "Association for Computational Linguistics",
    url = "https://aclanthology.org/2023.sustainlp-1.23",
    doi = "10.18653/v1/2023.sustainlp-1.23",
    pages = "290--298",
}