Efficient Vector Store System for Python using Shared Memory

Abstract

Many e-commerce companies use machine learning to make customer experience better. Even within a single company, there will be generally many independent services running, each specializing in some aspect of customer experience. Since machine learning models work on abstract vectors representing users and/or items, each such service needs a way to store these vectors. A common approach nowadays is to save them in in-memory caches like Memcached. As these caches run in their own processes, and Machine Learning services generally run as Python services, there is a communication overhead involved for each request that ML service serves. One can reduce this overhead by directly storing these vectors in a Python dictionary within the service. To support concurrency and scale, a single node runs multiple instances of the same service. Thus, we also want to avoid duplicating these vectors across multiple processes. In this paper, we propose a system to store vectors in shared memory and efficiently serve all concurrent instances of the service, without replicating the vectors themselves. We achieve up to 4.5x improvements in latency compared to Memcached. Additionally, due to availability of more memory, we can increase the number of server processes running in each node, translating into greater throughput. We also discuss the impact of the proposed method (towards increasing the throughput) in live production scenario.