Unleashing Graph Partitioning for Large-Scale Nearest Neighbor Search
(2403.01797)Abstract
We consider the fundamental problem of decomposing a large-scale approximate nearest neighbor search (ANNS) problem into smaller sub-problems. The goal is to partition the input points into neighborhood-preserving shards, so that the nearest neighbors of any point are contained in only a few shards. When a query arrives, a routing algorithm is used to identify the shards which should be searched for its nearest neighbors. This approach forms the backbone of distributed ANNS, where the dataset is so large that it must be split across multiple machines. In this paper, we design simple and highly efficient routing methods, and prove strong theoretical guarantees on their performance. A crucial characteristic of our routing algorithms is that they are inherently modular, and can be used with any partitioning method. This addresses a key drawback of prior approaches, where the routing algorithms are inextricably linked to their associated partitioning method. In particular, our new routing methods enable the use of balanced graph partitioning, which is a high-quality partitioning method without a naturally associated routing algorithm. Thus, we provide the first methods for routing using balanced graph partitioning that are extremely fast to train, admit low latency, and achieve high recall. We provide a comprehensive evaluation of our full partitioning and routing pipeline on billion-scale datasets, where it outperforms existing scalable partitioning methods by significant margins, achieving up to 2.14x higher QPS at 90% recall$@10$ than the best competitor.
Overview
-
The paper explores the use of graph partitioning to improve approximate nearest neighbor search (ANNS) for large datasets, presenting new routing methods with theoretical performance guarantees.
-
Introduces two novel routing methods, kRt and hRt, adaptable to any partitioning strategy and improving query performance.
-
Offers theoretical contributions and empirical evidence showcasing the effectiveness of balanced graph partitioning and combinatorial routing in achieving high throughput.
-
Suggests future research directions aimed at enhancing routing efficiency, investigating index compression, and applying methods in heterogeneous computing environments.
Unleashing Graph Partitioning for Enhanced Large-Scale Nearest Neighbor Search Performance
Introduction to the Research Problem
Nearest neighbor search (NNS) is a computational routine pivotal in a spectrum of applications across computer vision, information retrieval, and machine learning domains. Given the challenges associated with performing NNS in high-dimensional spaces, particularly the curse of dimensionality, approximate nearest neighbor search (ANNS) has emerged as a practical alternative. Traditionally, techniques such as quantization and the employment of various index data structures have been the focus of ANNS solutions. However, the distributed execution of ANNS, necessary for handling datasets of a billion-scale magnitude, introduces unique challenges. This paper addresses the decomposition of a large-scale ANNS problem into smaller sub-problems, utilizing graph partitioning for the efficient and effective distribution of data.
Advancements in Partitioning and Routing
The paper marks a significant step forward in the deployment of graph partitioning methods for ANNS by devising highly efficient routing methods accompanied by strong theoretical performance guarantees. The methods introduced are distinguished by their modularity, allowing for their application with any partitioning methodology.
- Fast, Inexact Graph Building: Demonstrates that an approximate k-nearest neighbor graph, despite being built through a simplified, inexact process, can effectively partition the dataset without compromising query performance.
- Fast, Accurate, and Modular Combinatorial Routing: Introduces two novel routing methods, named kRt (based on hierarchical k-means) and hRt (based on locality sensitive hashing), which are both efficient and adaptable to various partitioning strategies.
- Theoretical Guarantees for Routing: Provides the first analytical exploration of routing performance, presenting theoretical guarantees reaffirming the effectiveness of the hRt method.
- Empirical Evaluation: Conducts a thorough empirical analysis revealing that partitions achieved via balanced graph partitioning procured a marked improvement in throughput, surpassing existing methods significantly with up to 2.14x higher queries per second (QPS) at a recall rate of 90%.
Theoretical and Practical Implications
The theoretical contributions elucidate the robust foundations of the proposed routing strategies, notably the hRt variant, by establishing guarantees of routing effectiveness. On a practical level, the empirical results provide convincing evidence of the superiority of graph partitioning, particularly in scenarios characterized by extremely large datasets. Notably, the combinatorial routing methods not only deliver high recall but also demonstrate remarkable speed in training compared to neural network approaches, showcasing a significant reduction in computational resource requirements.
Future Directions
The research opens several avenues for further exploration. More sophisticated routing accuracy and efficiency improvements remain a promising area of research. Investigating routing index compression through quantization could yield more space-efficient solutions without sacrificing performance. Additionally, exploring partitioning cost functions optimized for ANNS beyond the first shard could offer more nuanced shard retrieval strategies. Another area ripe for investigation is the application of these graph partitioning and routing strategies across heterogeneous computing environments, including GPUs, which could further enhance the scalability and efficiency of distributed ANNS systems.
Conclusion
By addressing the limitations of prior work and introducing groundbreaking routing methodologies with strong theoretical underpinnings, this study significantly advances the field of distributed ANNS. The combined use of balanced graph partitioning with the modular, highly efficient routing methods proposed herein sets a new benchmark for large-scale ANNS performance, potentially reshaping future approaches to handling billion-scale datasets in high-dimensional spaces.
Create an account to read this summary for free: