Automated Detection of Serializability Violations under Weak Consistency
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While a number of weak consistency mechanisms have been developed in recent years to improve performance and ensure availability in distributed, replicated systems, ensuring correctness of transactional applications running on top of such systems remains a difficult and important problem. Serializability is a well-understood correctness criterion for transactional programs; understanding whether applications are serializable when executed in a weakly-consistent environment, however remains a challenging exercise. In this work, we combine the dependency graph-based characterization of serializability and the framework of abstract executions to develop a fully automated approach for statically finding bounded serializability violations under any weak consistency model. We reduce the problem of serializability to satisfiability of a formula in First-Order Logic, which allows us to harness the power of existing SMT solvers. We provide rules to automatically construct the FOL encoding from programs written in SQL (allowing loops and conditionals) and the consistency specification written as a formula in FOL. In addition to detecting bounded serializability violations, we also provide two orthogonal schemes to reason about unbounded executions by providing sufficient conditions (in the form of FOL formulae) whose satisfiability would imply the absence of anomalies in any arbitrary execution. We have applied the proposed technique on TPC-C, a real world database program with complex application logic, and were able to discover anomalies under Parallel Snapshot Isolation, and verify serializability for unbounded executions under Snapshot Isolation, two consistency mechanisms substantially weaker than serializability.
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