Qobra: Fast Verification of Transactional Serializability with Quantum Annealing

Serializability is a standard to guarantee the correct execution of database operations. Since cloud databases do not always guarantee serializability, users must check for serializability on their own. However, the internal of 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. Previous research 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. The evaluation results show that the proposed method is 751-890 times faster than state of the art method.