Challenge: Dense passage retrieval improves ranking accuracy in open-domain question answering but at the cost of large space and memory requirements.
Approach: They propose a simple unsupervised pipeline that includes principal component analysis (PCA), product quantization, and hybrid search to improve space efficiency.
Outcome: The proposed pipeline achieves good accuracy–space trade-offs, for example, 48 compression with less than 3% drop in top-100 retrieval accuracy on average or 96 compression without drop in space requirements.

Similar Papers

Dense Passage Retrieval for Open-Domain Question Answering (2020.emnlp-main)

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Challenge: Open-domain question answering relies on efficient passage retrieval to select candidate contexts.
Approach: They propose a dual-encoder framework that can be implemented to retrieve passages from a small number of questions and passages.
Outcome: The proposed system outperforms a strong Lucene-BM25 system in top-20 passage retrieval accuracy on multiple open-domain QA benchmarks.
CompAct: Compressing Retrieved Documents Actively for Question Answering (2024.emnlp-main)

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Challenge: Existing methods to condense extensive documents with no loss of information are difficult to implement in real-world scenarios.
Approach: They propose a framework that employs an active strategy to condense extensive documents without losing key information.
Outcome: The proposed framework improves performance and compression rate on multi-hop question-answering benchmarks.
Extremely efficient online query encoding for dense retrieval (2024.findings-naacl)

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Challenge: Existing dense retrieval systems use the same model architecture for encoding both passages and queries, even though queries are much shorter and simpler than passages.
Approach: They propose a small efficient RNN query encoder that can reduce latency by 12 with only a minor decrease in quality.
Outcome: The proposed solution reduces latency by up to 12 while achieving 35.5 MRR@10 score.
How Does Generative Retrieval Scale to Millions of Passages? (2023.emnlp-main)

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Challenge: generative retrieval is a new paradigm for information retrieval, enabling a sequence-to-sequence model with a single Transformer . generative encoders have been used on small corpora, but only on large ones .
Approach: They propose to encode an entire document corpus within a single Transformer . they find generative retrieval is competitive with state-of-the-art dual encoders on small corpora .
Outcome: The proposed approach is competitive with state-of-the-art dual encoders on small corpora, the study finds . the proposed approach only evaluates on document corporales on the order of 100K in size .
The Curse of Dense Low-Dimensional Information Retrieval for Large Index Sizes (2021.acl-short)

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Challenge: Existing studies have shown that dense representations outperform sparse representations with large index sizes.
Approach: They propose to use dense low-dimensional representations to retrieve relevant documents . they show performance decreases quicker for increasing index sizes than for sparse representations .
Outcome: The proposed representations outperform sparse representations with large index sizes.
PISCO: Pretty Simple Compression for Retrieval-Augmented Generation (2025.findings-acl)

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Challenge: Document compression methods suffer from accuracy losses and limited context size.
Approach: They propose a method that achieves a 16x compression rate with minimal accuracy loss . they show that PISCO outperforms existing compression models by 8% in accuracy .
Outcome: The proposed method outperforms existing compression models by 8% in accuracy.
Decoding Dense Embeddings: Sparse Autoencoders for Interpreting and Discretizing Dense Retrieval (2025.emnlp-main)

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Challenge: Existing sparse retrieval methods suffer from a lack of interpretability . we propose a new interpretability framework that decomposes dense embeddings into distinct, interpretable latent concepts.
Approach: They propose a new interpretability framework that leveragesSparse Autoencoders to decompose uninterpretable dense embeddings fromDPR models into distinct, interpretable latent concepts.
Outcome: The proposed interpretability framework achieves high index-space and computational efficiency while maintaining robust performance across vocabulary and semantic mismatches.
Generative Dense Retrieval: Memory Can Be a Burden (2024.eacl-long)

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Challenge: Empirical results show that Generative Dense Retrieval (GDR) achieves an average of 3.0 R@100 improvement on NQ dataset under multiple settings and has better scalability.
Approach: They propose a Generative Dense Retrieval paradigm that auto-decodes document identifiers given a query and uses memory to avoid memory confusion.
Outcome: Empirical results show that the proposed paradigm improves on the small-scale corpora and improves scalability.
Efficient Passage Retrieval with Hashing for Open-domain Question Answering (2021.acl-short)

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Challenge: Open-domain question answering systems often require large memory to run because of the massive size of their passage index.
Approach: They propose a memory-efficient neural retrieval model that integrates a learning-to-hash technique into the state-of-the-art Dense Passage Retriever to represent the passage index using compact binary codes.
Outcome: The proposed model significantly reduces memory cost from 65GB to 2GB without loss of accuracy on two open-domain question answering benchmarks.
Unsupervised Corpus Aware Language Model Pre-training for Dense Passage Retrieval (2022.acl-long)

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Challenge: Recent research shows that fine-tuning dense retrievers to realize their capacity requires carefully designed fine-cuning techniques.
Approach: They propose a pre-training architecture that learns to condense information into the dense vector through LM pre-training and a coCondenser architecture which adds an unsupervised corpus-level contrastive loss to warm up the passage embedding space.
Outcome: The proposed architecture reduces the need for heavy data engineering and large batch training.

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