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On Deferred Constraints in Distributed Database Systems

机译：分布式数据库系统中的延迟约束

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An atomic commit protocol (ACP) is a distributed algorithm used to ensure the atomicity property of transactions in distributed database systems. Although ACPs are designed to guarantee atomicity, they add a significant extra cost to each transaction execution time. This added cost is due to the overhead of the required coordination messages and log writes at each involved database site to achieve atomicity. For this reason, the continuing research efforts led to a number of optimizations that reduce the aforementioned cost. The most commonly adopted optimizations in the database standards and commercial database management systems are those designed around the early release of read locks of transactions. In this type of optimizations, certain participating sites may start releasing the read locks held by transactions before they are fully terminated across all participants. Hence, greatly enhancing concurrency among executing transactions and, consequently, the overall system performance. However, this type of optimizations introduces possible "execution infections" in the presence of deferred consistency constraints; a devastating complication that may lead to non-serializable executions of transactions. Thus, this type of optimizations could be considered useless, given the importance of preserving the consistency of the database in presence of deferred constraints, unless this complication is resolved in a practical and efficient manner. This is the essence of the "unsolicited deferred consistency constraints validation" mechanism presented in this paper
机译：原子提交协议（ACP）是一种分布式算法，用于确保分布式数据库系统中事务的原子性。尽管ACP旨在保证原子性，但它们会增加每个事务执行时间的大量额外成本。之所以增加成本，是因为需要协调消息和在每个涉及的数据库站点上写入日志以实现原子性的开销。由于这个原因，持续的研究工作导致了许多降低上述成本的优化。数据库标准和商业数据库管理系统中最常用的优化是围绕事务的读取锁的早期发布而设计的。在这种类型的优化中，某些参与站点可能会在所有参与者完全终止之前开始释放事务持有的读取锁。因此，极大地增强了执行事务之间的并发性，从而提高了整个系统的性能。但是，在存在延迟的一致性约束的情况下，这种类型的优化会引入可能的“执行感染”。破坏性的并发症，可能导致交易无法序列化执行。因此，考虑到在存在延迟约束的情况下保持数据库一致性的重要性，除非以实际有效的方式解决这种复杂性，否则这种类型的优化可能被认为是无用的。这是本文提出的“未经请求的递延一致性约束验证”机制的本质

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