Unsupervised Space Partitioning for Nearest Neighbor Search

TL;DR

This paper introduces an unsupervised, end-to-end learning framework for space partitioning in Approximate Nearest Neighbor Search that outperforms existing methods without requiring dataset pre-processing.

Contribution

It presents a novel unsupervised multi-objective loss function and ensembling technique for space partitioning, improving ANNS performance and efficiency over traditional clustering methods.

Findings

Outperforms state-of-the-art partitioning methods on benchmarks.

Requires fewer parameters and shorter training times.

Enhances existing ANNS techniques like ScaNN significantly.

Abstract

Approximate Nearest Neighbor Search (ANNS) in high dimensional spaces is crucial for many real-life applications (e.g., e-commerce, web, multimedia, etc.) dealing with an abundance of data. This paper proposes an end-to-end learning framework that couples the partitioning (one critical step of ANNS) and learning-to-search steps using a custom loss function. A key advantage of our proposed solution is that it does not require any expensive pre-processing of the dataset, which is one of the critical limitations of the state-of-the-art approach. We achieve the above edge by formulating a multi-objective custom loss function that does not need ground truth labels to quantify the quality of a given data-space partition, making it entirely unsupervised. We also propose an ensembling technique by adding varying input weights to the loss function to train an ensemble of models to enhance the search quality. On several standard benchmarks for ANNS, we show that our method beats the state-of-the-art space partitioning method and the ubiquitous K-means clustering method while using fewer parameters and shorter offline training times. We also show that incorporating our space-partitioning strategy into state-of-the-art ANNS techniques such as ScaNN can improve their performance significantly. Finally, we present our unsupervised partitioning approach as a promising alternative to many widely used clustering methods, such as K-means clustering and DBSCAN.