ITR: Cache-Resident Databases

摘要数据库是信息经济的核心。数据库性能是一个驱动因素，它决定了通过使用信息技术可以实现什么。虽然数据库管理系统自几十年前发明以来一直在发展，但不幸的是，考虑到当今最先进的计算机内存层次结构（未来甚至会更加如此），它们当前的设计已经过时了。本项目旨在缓解这一问题。虽然处理器速度每年翻一番，但内存访问速度遵循的改进曲线要浅得多。为了弥补这一速度差距，人们使用了一种被称为缓存的小型快速存储器来保存频繁访问的数据和靠近处理器的指令。在执行数据库工作负载时，访问通常会在（快速）缓存中丢失，而访问（慢速）内存，从而显著降低性能。硬件方法通常受到访问时间限制和对各种工作负载的适用性的限制。为了保持硬件设计的可行性，缓存通常使用简单的数据放置和替换方案，并且忽略了应用程序的内存访问行为。相反，缓存敏感的软件方法非常有前途。所提出的算法收集数据统计信息，以便对具有相似使用模式的数据进行正确分组，并优化缓存利用率。通过仔细观察行为，数据在使用之前被预取到缓存中。初步结果表明，这些技术(i)最大限度地减少了缓存中的失败次数，（ii）大大减少了产生的惩罚。

AbstractDatabases are at the very heart of the information economy. Databaseperformance is a driving factor that dictates what is possible through theuse of information technology. While database management systems haveevolved since they were invented several decades ago, their current designis unfortunately antiquated given the state-of-the-art computer memoryhierarchies of today (and even more so tomorrow). This project seeks toalleviate this problem.While processor speeds double every year, memory access speeds follow amuch shallower improvement curve. To bridge this speed gap, small, fastmemories called caches are used to hold frequently accessed data andinstructions close to the processor. When executing database workloads,accesses often miss in the (fast) cache and access the (slow) memory,thereby reducing performance significantly. Hardware approaches aretypically limited by access time constraints and by applicability to a widerange of workloads. To keep the hardware design feasible, caches typicallyuse simplistic data placement and replacement schemes, and are oblivious tothe memory access behavior of the application.Cache-conscious software methods are, on the contrary, extremely promising.The proposed algorithms collect data statistics in order to correctly groupdata with similar usage patterns and optimize cache utilization. Bycarefully observing behavior, data is prefetched into the cache before itis used. Preliminary results demonstrate that these techniques (i) minimizethe number of misses in the cache and (ii) significantly reduce theincurred penalties.