A Commit Strategy for Distributed Real-Time Transaction

Ramamritham gives three common typesof constraints for the execution history of concurrent transactions.This paper extends the constraints and gives the fourth type ofconstraint. Then the weak commit dependency and abort dependency betweentransactions, because of data access conflicts, are analyzed. Based on theanalysis, an optimistic commit protocol 2LC (two-Level Commit) isproposed, which is specially designed for the distributed real-timedomain. It allows transactions to optimistically access the locked datain a controlled manner, which reduces the data inaccessibility andpriority inversion inherent and undesirable in distributed real-time databasesystems. Furthermore, if the prepared transaction is aborted, thetransactions in its weak commit dependency set will execute as normalaccording to 2LC. Extensive simulation experiments have been performedto compare the performance of 2LC with that of the base protocol, the permitsreading of modified prepared-data for timeliness (PROMPT) and thedeadline-driven conflict resolution (DDCR). The simulation results showthat 2LC is effective in reducing the number of missed transactiondeadlines. Furthermore, it is easy to be incorporated with the existingconcurrency control protocols.