example transfer money from bank a to bank b debit a c - PDF document

¥!Example: transfer money from bank A to bank B Ð!Debit A, credit B, tell client ÒOKÓ ¥!Want both to do it or neither to do it ¥!Never want only one side to act Ð!Better if nothing happens! ¥ Serializability: Ð!Series of operations requested by users Ð!Outside observer sees them each complete atomically in some complete order Ð!Requires support for locking ¥!Recoverability: Ð!Each operation executes completely or not at all; Òall-or-nothing semanticsÓ Ð!No partial results Serializability: Ð!Series of operations requested by users Ð!Outside observer sees them each complete atomically in some complete order Ð!Requires support for locking ¥!Recoverability: Ð!Each operation executes completely or not at all; Òall-or-nothing semanticsÓ Ð!No partial results ¥!Not enough money in AÕs bank account Ð!A doesnÕt commit, B does ¥!BÕs bank account no longer exists Ð!A commits, B doesnÕt ¥!Network link to B broken Ð TC, A, and B have separate notions of committing ¥!Safety Ð!(Really, Òcorrect executionÓ) Ð!If one commits, no one aborts If one aborts, no one commits A and B wait for ÒcommitÓ/ÓabortÓ from TC ¥!Making progress when TC waits for ÒyesÓ/ÓnoÓ Ð!TC not yet sent any ÒcommitÓ messages B sends ÒstatusÓ request message to A, asking if A Ð Ð