Recursive Computation Over Relational Data (RECORD)

让您的计算更贴近数据！数据库社区的这句古老的咒语断言，我们可以期待一个可以立即访问数据的SQL查询引擎比我们必须首先将数据传送到的外部处理器的性能要好得多。如果计算是类似查询的，并且主要涉及过滤、数据(重新)组合、分组或聚合，那么这个传说就成立了。对于依赖于任意迭代控制流或递归的复杂算法如何在相同的SQL引擎中进行有效评估，目前还不太清楚。随着SQL：1999的出现，当代数据库引擎开始支持递归形式。然而，相关的语言构造表现出语法限制，基于常规开发人员难以理解的语义，或者表现出令人警醒的运行时性能，这往往使迭代或递归的SQL不切实际。Project Record探索了编译和实现技术，这些技术(1)以可读、简洁(甚至优雅)的方式接受迭代和递归算法的公式，(2)使用关系数据库系统作为高效和可伸缩的运行时环境，在数据旁边执行计算。我们采用最初由(函数式)编程语言社区开发的既定技术，然后对这些思想进行调整和调整，使其适用于递归SQL函数以及以命令式风格编写的迭代PL/SQL过程。我们的重点是不会颠覆现有数据库技术的非侵入性方法：因此，我们将函数和过程映射到已经内置到现成数据库系统中的本机、普通的SQL递归构造。然而，我们可以自由地对数据库内核应用外科手术更改，在这些更改中，我们预期运行时性能或系统的空间使用可以受益。不乏数据密集型问题领域，它们对这种数据库内计算的需求只会越来越大。Record将研究这些领域的核心数据结构和算法，以测试其结果，并证明关系数据上的递归计算确实是实用和有效的。

Move your computation close to the data! This age-old mantra of the database community asserts that we can expect a SQL query engine with immediate access to the data to perform significantly better than an external processor to which we have to ship the data first. The lore holds up if the computation is query-like and primarily involves filtering, data (re-)combination, grouping, or aggregation. It is much less clear how complex algorithms that rely on arbitrary iterative control flow or recursion can be efficiently evaluated inside the same SQL engines. With the advent of SQL:1999, contemporary database engines started to support forms of recursion. The associated language constructs, however, exhibit syntactic restrictions, are based on semantics that are tough to grasp for regular developers, or exhibit sobering runtime performance that often render iterative or recursive SQL impractical. Project RECORD explores compilation and implementation techniques that (1) admit the formulation of iterative and recursive algorithms in a readable, concise (even elegant) fashion and (2) use relational database systems as efficient and scalable runtime environments that perform the computation right next to the data. We adopt established techniques originally developed by the (functional) programming language community, then adapt and bend these ideas so that they apply to recursive SQL functions as well as iterative PL/SQL procedures written in an imperative style. Our focus is on non-invasive approaches that do not turn existing database technology on its head: we thus map functions and procedures to the native, plain SQL recursion constructs already built into off-the-shelf database systems. We take the freedom, however, to apply surgical changes to database kernels where we anticipate that the runtime performance or the systems' space usage can benefit. There is no shortage of data-intensive problem domains whose need for such in-database computation only ever goes up. RECORD will study the core data structures and algorithms of these domains to test-drive its results and to prove that recursive computation over relational data can indeed be practical and efficient.