A Tree-Structured Two-Phase Commit Framework for OceanBase: Optimizing Scalability and Consistency

Distributed transactional consistency over partitions is costly: classical two-phase commit (2PC) incurs high coordination and latency, and dynamic partition transfers complicate recovery. We introduce a tree-structured 2PC framework for OceanBase (OB) using single-machine log streams in three ways. First, we use log streams as coalesced 2PC participants: co-located partitions that would each be separate in a partition-centric design share one log-stream participant, so a transaction spanning N such partitions interacts with one participant in commit, cutting coordination by orders of magnitude (e.g., 99% for N = 100). Second, a coordinator-rooted DAG recursively builds commit trees; migration contexts as leaves avoid explicit participant-list updates and circular dependencies while ensuring linearizable commits under topology change. Third, prepare_unknown and trans_unknown states prevent violations when participants lose context; they signal uncertainty during retries, avoiding erroneous aborts from "lying" participants while isolating users from ambiguity. Experiments approach single-machine transaction performance with lower latency and bandwidth consumption, supporting modern distributed databases.