Timestamp-Based Orphan Elimination

An orphan in a distributed transaction system is an activity executing on behalf of an aborted transaction. Orphans are undesirable because they waste system resources and because they may observe inconsistent data. This paper proposes a new method for managing orphans created by crashes and by aborts. The method ensures that orphans are detected and eliminated in a timely manner, and it prevents them from observing inconsistent states. A major advantage of this method is simplicity: it is easy to understand, to implement , and to prove correct. An " eager " version of this method uses approximately synchronized real-time clocks to ensure that orphans are eliminated within a fixed duration, and a " lazy " version uses logical clocks to ensure that orphans are eventually eliminated as information propagates through the system. The method is fail-safe: unsyn-chronized clocks and lost messages may affect performance, but they cannot produce inconsistencies or protect orphans from eventual elimination .