An Analysis of Deadlock Detection Schemes in Multidatabase Systems

In multidatabase systems, autonomous executions of concurrency control schemes at local sites make it diicult to detect global deadlocks. Though time-out schemes are able to detect transactions involved in deadlocks, they may include false deadlocks. It is believed that an approximate wait-for-graph(AWFG) helps reduce the false deadlocks by extending the time-out values for those that appear not to be involved in a deadlock. In this paper, we evaluate the eeectiveness of the AWFG scheme in reducing false deadlocks and the eeect of the time-out value. Our simulation studies show that the AWFG scheme is not eecient in reducing false deadlocks since it is unaware of the exact waiting states in each local DBMS. We also found that the optimal time-out value is sensitive to the change in the transaction abort rate, and it is insensitive to the data contention level of global transactions, contrary to the common belief.