Many organizations deploy applications that use databases by sending Structured Query Language (SQL) statements to them and obtaining data that result from the execution of these statements. Since applications often share the same databases concurrently, database deadlocks routinely occur in these databases resulting in major performance degradation in these applications. Database engines do not prevent database deadlocks for the same reason that the schedulers of operating system kernels do not preempt processes in a way to avoid race conditions and deadlocks - it is not feasible to find an optimal context switching schedule quickly for multiple processes (and SQL statements), and the overhead of doing it is prohibitive.

In this demonstration, we will present a database deadlocks prevention system that visualizes our algorithm for detecting hold-and-wait cycles that specify how resources (e.g., database tables) are locked and waited on to be locked during executions of SQL statements and utilizes those cycles information to prevent database deadlocks automatically.

We define a method for the automatic generation of supervisory controllers that force a plant to perform a given operation by a given deadline. The operation must be executed by a prespecified delay λ with respect to the previous execution of the operation. Although our supervisor generation occurs offline with respect to plant execution, the resulting controllers automatically take into account variable task durations in an effort to increase the flexibility of operation schedules in the controlled plant. We model both the controlled plant and control supervisors as time Petri nets. In this setting, our control supervisors must force a target transitiontdto fire within λ time units since the previous firing oftd. Our supervisor generation is based on the concept of a transition latency. The latency of a Petri net transitiontis the time interval during whichtmust be disabled in order for target transitiontdto fire by its deadline. If a transitiontthat may delay the firing oftdhas latencyl(t), thentmust be disabled at leastl(t) time units before the expiration of the deadline ontd. In this paper, we discuss in detail two algorithms for generating transition latencies, and we show an application to a maintenance system.

We automatically synthesize supervisory controllers that force a system to perform a certain operation by a given deadline. The operation must be executed by a pre-specified delay λ with respect to the previous execution of the operation. We model both the controlled system and our control supervisors as time Petri nets. Given a target transition and a deadline, our supervisors disable net behaviors in which the firing of the target transition may miss the deadline. Our method is subject to a merge exclusion assumption on the structure of paths contained in a so-called net unfolding. If a control problem does not satisfy this assumption, we abandon supervisor generation. Preliminary empirical results show that our method is both relatively general and more tractable from a computational standpoint than most other real-time analysis methods.