更好地理解和评估Flash SSD上的树结构
Toward a Better Understanding and Evaluation of Tree Structures on Flash SSDs
摘要：
固态驱动器（SSD）广泛用于部署持久性数据存储，因为它们提供低延迟随机访问、高写入吞吐量、高数据密度和低成本。基于树的数据结构被广泛用于构建持久数据存储，实际上，它们是当今生产和研究中使用的许多数据管理系统的骨干。在本文中，我们表明，基准测试的持久树为基础的数据结构的SSD是一个复杂的过程，这可能很容易招致微妙的陷阱，可能会导致不准确的性能评估。在高层次上，这些陷阱源于在复杂硬件上运行的复杂软件的交互。一方面，树结构实现了对性能有重要影响的内部操作。另一方面，SSD采用固件逻辑来处理底层闪存的特性，众所周知，这些特性会导致复杂的性能动态。我们使用RocksDB和WiredTiger（LSM树和B+树的两种广泛实现）确定了七个基准测试陷阱。我们发现，这样的陷阱可能会导致关键性能指标的不正确测量，阻碍了结果的可重复性和代表性，并导致在生产环境中的次优部署。我们还提供了如何避免这些陷阱，以获得更可靠的性能测量，并在不同的设计点之间进行更彻底和公平的比较的指导方针。
英文摘要：
Solid-state drives (SSDs) are extensively used to deploy persistent data stores, as they provide low latency random access, high write throughput, high data density, and low cost. Tree-based data structures are widely used to build persistent data stores, and indeed they lie at the backbone of many of the data management systems used in production and research today. In this paper, we show that benchmarking a persistent tree-based data structure on an SSD is a complex process, which may easily incur subtle pitfalls that can lead to an inaccurate performance assessment. At a high-level, these pitfalls stem from the interaction of complex software running on complex hardware. On one hand, tree structures implement internal operations that have nontrivial effects on performance. On the other hand, SSDs employ firmware logic to deal with the idiosyncrasies of the underlying flash memory, which are well known to lead to complex performance dynamics. We identify seven benchmarking pitfalls using RocksDB and WiredTiger, two widespread implementations of an LSM-Tree and a B+Tree, respectively. We show that such pitfalls can lead to incorrect measurements of key performance indicators, hinder the reproducibility and the representativeness of the results, and lead to suboptimal deployments in production environments. We also provide guidelines on how to avoid these pitfalls to obtain more reliable performance measurements, and to perform more thorough and fair comparison among different design points.
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