非单调快照隔离
Non-Monotonic Snapshot Isolation
摘要：
许多分布式应用程序需要事务。然而，需要强同步的事务协议在大规模环境中是昂贵的。两个属性有助于事务系统的可伸缩性：真正的部分复制（GPR），它利用了工作负载的内在并行性，以及快照隔离（SI），它减少了对同步的需求。我们表明，在标准的假设下（数据存储访问是事先不知道的，事务可以访问数据存储中的任意对象），这是不可能的SI和GPR。为了避免这种不可能性，我们提出了一个较弱的一致性标准，称为非单调快照隔离（NMSI）。NMSI保留了SI的最重要属性，即，只读事务总是提交，并且两个写冲突的更新不会都提交。我们提出了一个GPR协议，确保NMSI，并具有较低的消息成本（即，它比先前的方法接触更少的副本和/或更快地提交）。
英文摘要：
Many distributed applications require transactions. However, transactional protocols that require strong synchronization are costly in large scale environments. Two properties help with scalability of a transactional system: genuine partial replication (GPR), which leverages the intrinsic parallelism of a workload, and snapshot isolation (SI), which decreases the need for synchronization. We show that, under standard assumptions (data store accesses are not known in advance, and transactions may access arbitrary objects in the data store), it is impossible to have both SI and GPR. To circumvent this impossibility, we propose a weaker consistency criterion, called Non-monotonic Snapshot Isolation (NMSI). NMSI retains the most important properties of SI, i.e., read-only transactions always commit, and two write-conflicting updates do not both commit. We present a GPR protocol that ensures NMSI, and has lower message cost (i.e., it contacts fewer replicas and/or commits faster) than previous approaches.
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