Umbra: A Disk-Based System with In-Memory Performance
Umbra: A Disk-Based System with In-Memory Performance
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发表时间：
2020
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通讯作者：
Thomas Neumann;M. Freitag
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作者：
Thomas Neumann;M. Freitag
在过去的十年中，主存大小的增加使得纯内存数据库系统变得可行，内存系统提供了前所未有的性能。然而，DRAM仍然相对昂贵，而且主内存大小的增长已经放缓。相比之下，固态硬盘的价格在过去几年里大幅下降，其读取带宽已增加到每秒千兆字节。这使得将大容量内存缓冲区与快速SSD作为存储设备相结合，将内存中工作集的卓越性能与基于磁盘的系统的可扩展性结合在一起是很有吸引力的。在本文中，我们介绍了Umbra系统，这是纯内存超级系统向基于磁盘的系统，或者更确切地说，基于SSD的系统的演变。我们表明，通过引入一种新颖的具有可变大小页面的低开销缓冲区管理器，对于缓存的工作集，我们可以获得与内存数据库系统相当的性能，同时优雅地处理对未缓存数据的访问。我们讨论了以较低的开销优雅地处理内存不足的情况所需的更改和技术，为基于内存优化的基于磁盘的系统的设计提供了见解。
The increases in main-memory sizes over the last decade have made pure in-memory database systems feasible, and in-memory systems offer unprecedented performance. However, DRAM is still relatively expensive, and the growth of main-memory sizes has slowed down. In contrast, the prices for SSDs have fallen substantially in the last years, and their read bandwidth has increased to gigabytes per second. This makes it attractive to combine a large in-memory buffer with fast SSDs as storage devices, combining the excellent performance for the in-memory working set with the scalability of a disk-based system. In this paper we present the Umbra system, an evolution of the pure in-memory HyPer system towards a disk-based, or rather SSD-based, system. We show that by introducing a novel low-overhead buffer manager with variable-size pages we can achieve comparable performance to an in-memory database system for the cached working set, while handling accesses to uncached data gracefully. We discuss the changes and techniques that were necessary to handle the out-of-memory case gracefully and with low overhead, offering insights into the design of a memory optimized disk-based system.