Hash tables are possibly the single most researched element of the database query processing layers. There are many good reasons for that. They are critical for some key operations like joins and aggregation, and as such are one of the largest contributors to the overall query performance. Their efficiency is heavily impacted by variations of workloads, hardware and implementation, leading to many research opportunities. At the same time, they are sufficiently small and local in scope, allowing a starting researcher, or even a student, to understand them and contribute novel ideas. And benchmark them. . . Oh, the benchmarks. . . :)

中文翻译：

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技术视角

哈希表可能是数据库查询处理层中研究最多的元素。这有很多很好的理由。它们对于连接和聚合等一些关键操作至关重要，因此是整体查询性能的最大贡献者之一。它们的效率受到工作负载、硬件和实施的变化的严重影响，从而带来了许多研究机会。同时，它们的范围足够小且具有局部性，允许初级研究人员甚至学生能够理解它们并提出新颖的想法。并对它们进行基准测试。. . 哦，基准。. . :)