Adaptive Representations for Semantic Search

Web-scale search systems use a large neural network to embed the query which is then hooked into a separate approximate nearest neighbour search (ANNS) pipeline to retrieve similar data points. Such approaches use a rigid – potentially high-dimensional – representation out of encoder to perform the entire search. This can be far from optimal accuracy-compute trade-off. In this paper, we argue that in different stages of ANNS, we can use representations of different capacities, adaptive representations, to ensure that the accuracy-compute tradeoff can be met nearly optimally. In particular, we introduce AdANNS, a novel ANNS design paradigm that explicitly leverages the flexibility and adaptive capabilities of the recently introduced Matryoshka Representations (Kusupati et al., 2022). We demonstrate that using AdANNS to construct the search data structure (AdANNS-C) provides state-of-the-art accuracy-compute tradeoff; AdANNS powered inverted file index (IVF) is up to 1.5% more accurate or up to 100× faster ImageNet-1K retrieval. We also show that matryoshka representations can power compute-aware adaptive search during inference (AdANNS-D) on a fixed ANNS (IVF) structure and be up to 16× faster for similar accuracy. Finally, we explore the applicability of adaptive representations across ANNS building blocks and further analyze the choice of matryoshka representations for semantic search.