At the heart of contemporary recommender systems (RSs) are latent factor models that provide quality recommendation experience to users. These models use embedding vectors, which are typically of a uniform and fixed size, to represent users and items. As the number of users and items continues to grow, this design becomes inefficient and hard to scale. Recent lightweight embedding methods have enabled different users and items to have diverse embedding sizes, but are commonly subject to two major drawbacks. Firstly, they limit the embedding size search to optimizing a heuristic balancing the recommendation quality and the memory complexity, where the trade-off coefficient needs to be manually tuned for every memory budget requested. The implicitly enforced memory complexity term can even fail to cap the parameter usage, making the resultant embedding table fail to meet the memory budget strictly. Secondly, most solutions, especially reinforcement learning based ones derive and optimize the embedding size for each each user/item on an instance-by-instance basis, which impedes the search efficiency. In this paper, we propose Budgeted Embedding Table (BET), a novel method that generates table-level actions (i.e., embedding sizes for all users and items) that is guaranteed to meet pre-specified memory budgets. Furthermore, by leveraging a set-based action formulation and engaging set representation learning, we present an innovative action search strategy powered by an action fitness predictor that efficiently evaluates each table-level action. Experiments have shown state-of-the-art performance on two real-world datasets when BET is paired with three popular recommender models under different memory budgets.

翻译：当代推荐系统的核心是潜在因子模型，这些模型为用户提供高质量推荐体验。这类模型使用统一固定大小的嵌入向量来表示用户和物品。随着用户和物品数量持续增长，这种设计变得低效且难以扩展。近期轻量级嵌入方法允许不同用户和物品具有不同嵌入大小，但普遍存在两大缺陷：其一，它们将嵌入大小搜索限制为优化平衡推荐质量与内存复杂度的启发式方法，其中权衡系数需要针对每个内存预算手动调整。这种隐式强制实施的内存复杂度项甚至可能无法限制参数使用量，导致最终生成的嵌入表无法严格满足内存预算。其二，大多数方案（尤其是基于强化学习的方法）需要逐实例推导并优化每个用户/物品的嵌入大小，这严重阻碍了搜索效率。本文提出预算化嵌入表（BET），这是一种能生成保证满足预设内存预算的表级动作（即为所有用户和物品分配嵌入大小）的新方法。此外，通过利用基于集合的动作表达并引入集合表示学习，我们提出了一种创新的动作搜索策略，该策略借助动作适应性预测器高效评估每个表级动作。实验表明，当BET与三种流行推荐模型在不同内存预算下配合使用时，在两个真实数据集上均达到最先进性能。