Qobra: Accelerating Transactional Serializability Verifier by Quantum Annealing

Serializability is a standard that guarantees the correct execution of database operations. Since cloud databases do not always guarantee serializability, users must check for serializability on their own. However, what operations are executed in the cloud databases is a black box for users, making it difficult for them to make a judgment. This is a combinatorial optimization problem called the “black-box serializability problem,” which is a satisfiability problem known to be NP-complete. A seminal work called Cobra has proposed an architecture that solves this problem using the SMT solver, a general-purpose solver for the satisfiability problem. Still, as the number of transactions increases, the search space will expand exponentially, so it becomes challenging to determine serializability. On the other hand, quantum annealing is excellent for fast-solving combinatorial optimization problems and can be applied to this satisfiability problem. This paper proposes a fast solver for the black-box serializability problem using quantum annealing extending Cobra. The evaluation results show that the proposed method is 751–890 times faster than Cobra.