Modern distributed databases face challenges in achieving transactional consistency across distributed partitions. Traditional two-phase commit (2PC) protocols incur high coordination overhead and latency, and require complex recovery for dynamic partition transfers. This paper introduces a novel tree-shaped 2PC framework for OceanBase that leverages single-machine log streams to address these challenges through three innovations. First, we propose log streams as atomic participants, replacing partition-level coordination. By treating each log stream as the commit unit, a transaction spanning $N$ co-located partitions interacts with one participant, reducing coordination overhead by orders of magnitude (e.g., 99 percent reduction for $N=100$). Second, we design a tree-shaped 2PC protocol with coordinator-rooted DAG topology that dynamically handles partition transfers by recursively constructing commit trees. When a partition migrates during a transaction, the protocol embeds migration contexts as leaf nodes, eliminating explicit participant list updates, resolving circular dependencies, and ensuring linearizable commits under topology changes. Third, we introduce prepare-unknown and trans-unknown states to prevent consistency violations when participants lose context. These states signal uncertainty during retries, avoiding erroneous aborts from so-called lying participants while isolating users from ambiguity. Experimental evaluation demonstrates performance approaching that of single-machine transactions, with reduced latency and bandwidth consumption, validating the framework's effectiveness for modern distributed databases.

翻译：现代分布式数据库在实现跨分布式分区的事务一致性方面面临挑战。传统的两阶段提交（2PC）协议存在协调开销高、延迟大等问题，且需要为动态分区转移设计复杂的恢复机制。本文提出一种面向OceanBase的新型树形2PC框架，该框架通过单机日志流技术，以三项创新应对这些挑战。首先，我们提出以日志流作为原子参与者，替代分区级协调机制。通过将每个日志流作为提交单元，一个跨越$N$个共置分区的事务仅需与一个参与者交互，使协调开销降低数个数量级（例如当$N=100$时减少99%）。其次，我们设计了基于协调器根节点有向无环图拓扑的树形2PC协议，该协议通过递归构建提交树动态处理分区转移。当事务执行期间发生分区迁移时，协议将迁移上下文嵌入为叶节点，从而消除显式的参与者列表更新，解决循环依赖问题，并确保拓扑变化下的线性化提交。第三，我们引入准备未知（prepare-unknown）和事务未知（trans-unknown）状态，防止参与者丢失上下文时出现一致性违例。这些状态在重试期间传递不确定性信号，避免因所谓“欺骗参与者”导致的错误中止，同时将用户与状态歧义隔离。实验评估表明，该框架在降低延迟和带宽消耗的同时，性能接近单机事务水平，验证了其对现代分布式数据库的有效性。