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Hierarchical BM25 enables billion-document lexical search with reduced memory

A new research paper introduces Hierarchical BM25, a method designed to make lexical search practical for massive document collections, such as one billion documents. Traditional BM25 indexing becomes computationally expensive and slow at this scale, requiring significant memory and disk access. Hierarchical BM25 achieves a substantial reduction in memory footprint to approximately 4.4 GB, independent of corpus size, and significantly improves query latency to around 300 ms. This approach sacrifices exact ranking for fixed bounds on memory and latency, enabling interactive search experiences over extremely large datasets. AI

IMPACT Enables more efficient and scalable search over massive text datasets, potentially impacting AI applications that rely on large-scale information retrieval.

RANK_REASON Academic paper detailing a new information retrieval technique. [lever_c_demoted from research: ic=1 ai=0.7]

Read on arXiv cs.IR (Information Retrieval) →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

Hierarchical BM25 enables billion-document lexical search with reduced memory

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  1. arXiv cs.IR (Information Retrieval) TIER_1 English(EN) · Swaminathan Sundararaman ·

    Hierarchical BM25: Lexical Search at Billion-Document Scale

    A flat BM25 index over one billion documents occupies about 400 GB. Holding it in memory requires DRAM proportional to corpus size. Serving it from disk takes 4-12 seconds per query. Exact top-k lexical retrieval at this scale is therefore impractical within an interactive latenc…