A commit strategy for distributed real-time transaction

Abstract

Ramamritham gives three common types of constraints for the execution history of concurrent transactions. This paper extends the constraints and gives the fourth type of constraint. Then the weak commit dependency and abort dependency between transactions, because of data access conflicts, are analyzed. Based on the analysis, an optimistic commit protocol 2LC (two-Level Commit) is proposed, which is specially designed for the distributed real-time domain. It allows transactions to optimistically access the locked data in a controlled manner, which reduces the data inaccessibility and priority inversion inherent and undesirable in distributed real-time database systems. Furthermore, if the prepared transaction is aborted, the transactions in its weak commit dependency set will execute as normal according to 2LC. Extensive simulation experiments have been performed to compare the performance of 2LC with that of the base protocol, the permits reading of modified prepared-data for timeliness (PROMPT) and the deadline-driven conflict resolution (DDCR). The simulation results show that 2LC is effective in reducing the number of missed transaction deadlines. Furthermore, it is easy to be incorporated with the existing concurrency control protocols.