RAIRS: Optimizing Redundant Assignment and List Layout for IVF-Based ANN Search

TL;DR

RAIRS introduces an optimized list selection metric and layout for IVF-based ANN search, significantly improving search efficiency and accuracy by reducing redundant computations and better handling Euclidean space queries.

Contribution

The paper proposes RAIRS, a novel approach combining an AIR metric and SEIL layout to optimize list assignment and reduce redundancy in IVF-based ANN search.

Findings

RAIRS outperforms existing solutions in real-world datasets.

Achieves up to 1.33x speedup over IVF-PQ Fast Scan with refinement.

Effectively reduces redundant distance computations.

Abstract

IVF is one of the most widely used ANNS (Approximate Nearest Neighbors Search) methods in vector databases. The idea of redundant assignment is to assign a data vector to more than one IVF lists for reducing the chance of missing true neighbors in IVF search. However, the naive strategy, which selects the second IVF list based on the distance between a data vector and the list centroids, performs poorly. Previous work focuses only on the inner product distance, while there is no optimized list selection study for the most popular Euclidean space. Moreover, the IVF search may access the same vector in more than one lists, resulting in redundant distance computation and decreasing query throughput. In this paper, we present RAIRS to address the above two challenges. For the challenge of the list selection, we propose an optimized AIR metric for the Euclidean space. AIR takes not only distances but also directions into consideration in order to support queries that are closer to the data vector but father away from the first chosen list's centroid. For the challenge of redundant distance computation, we propose SEIL, an optimized list layout that exploits shared cells to reduce repeated distance computations for IVF search. Our experimental results using representative real-world data sets show that RAIRS out-performs existing redundant assignment solutions and achieves up to 1.33x improvement over the best-performing IVF method, IVF-PQ Fast Scan with refinement.