presumedabort

Presumedabort is a term used in the context of distributed transaction processing, particularly within two-phase commit protocols and the recovery procedures that accompany them. It denotes a recovery state in which the outcome of a given transaction branch cannot be determined due to a failure or crash. In this situation, a transaction manager marks the branch as presumed abort to protect data consistency.

During a two-phase commit, a resource manager may participate in a transaction by promising to either commit or roll back if asked during the recovery phase. If a crash occurs before the final outcome is recorded, the recovery process may encounter insufficient information to confirm a commit. In such cases, the system can record the branch as presumed abort, meaning that the safest default action on recovery is to roll back the branch unless evidence later shows a committed outcome.

Presumed abort is distinct from an explicit abort or a committed outcome. It serves as a conservative recovery assumption: it avoids risking an unintended commit in the presence of failure, while allowing the system to complete the rollback once the transaction manager or resource manager recovers. Some implementations view presumed abort alongside heuristic outcomes, such as heuristic rollback or heuristic commit, as part of their recovery semantics in X/Open XA-compliant environments or similar distributed transaction frameworks.

See also: two-phase commit, XA specification, transaction recovery, heuristic outcomes.