论文标题
快照数据库的在线模式Evolution是免费的（几乎）
Online Schema Evolution is (Almost) Free for Snapshot Databases
论文作者
论文摘要
现代数据库应用程序通常会更改其模式，以跟上不断变化的要求。但是，在现有数据库系统中，对在线和交易架构进化的支持仍然具有挑战性。具体而言，先前的工作通常采用适用于现有系统的“补丁”来进行临时进化的方法，从而导致许多角色案例，并且通常不完整的功能。因此，申请通常必须仔细安排架构更改的下降，牺牲可用性。 本文介绍了Tesseract，这是一种新的在线和交易模式发展的方法，而无需上述缺点。我们基于关键观察设计Tesseract：在广泛使用的多次数据库系统中，架构进化可以建模为更改整个表的数据修改操作，即数据定义 - AS-Modification（DDAM）。这使我们能够通过利用并发控制协议来支持模式几乎“免费”。通过对现有快照隔离协议进行简单的调整，在40核服务器上，我们表明，在各种工作负载下，Tesseract能够在线提供，交易架构的进化而无需服务停机时间，并在架构进化进行进化时保持较高的应用程序性能。
Modern database applications often change their schemas to keep up with the changing requirements. However, support for online and transactional schema evolution remains challenging in existing database systems. Specifically, prior work often takes ad hoc approaches to schema evolution with 'patches' applied to existing systems, leading to many corner cases and often incomplete functionality. Applications therefore often have to carefully schedule downtimes for schema changes, sacrificing availability. This paper presents Tesseract, a new approach to online and transactional schema evolution without the aforementioned drawbacks. We design Tesseract based on a key observation: in widely used multi-versioned database systems, schema evolution can be modeled as data modification operations that change the entire table, i.e., data-definition-as-modification (DDaM). This allows us to support schema almost 'for free' by leveraging the concurrency control protocol. By simple tweaks to existing snapshot isolation protocols, on a 40-core server we show that under a variety of workloads, Tesseract is able to provide online, transactional schema evolution without service downtime, and retain high application performance when schema evolution is in progress.
