Hybrid protocols using dynamic adjustment of serialization order for real-time concurrency control

Time-critical scheduling in real-time database systems has two components: real-time scheduling and concurrency control. While both concurrency control and real-time scheduling are well-developed and well-understood, there is only limited knowledge about the integration of concurrency control and real-time scheduling. Though recently the problem has been studied actively, the proposed solutions are still at an initial stage. A major source of problems in integrating the two is the lack of coordination in the development. They are developed on different objectives and incompatible assumptions (Buchmann 1989). Most of the proposed work for real-time concurrency control employ a simple method to utilize one concurrency control scheme such as 2PL, TO and OCC, and to consider the priority of operations inherited from the timing constraints of transactions in operation scheduling. This method has an inherent disadvantage of being limited by the concurrency control method used as the base. Since neither of pessimistic nor optimistic concurrency control is satisfactory by itself for real-time scheduling, this simple method using only one control can hardly satisfy the timing requirements of RTDBS. Problems such as excessive blocking, wasted restarts, and priority inversion are serious in RTDBS. In this paper, we proposed two real-time transaction scheduling protocols which employ a hybrid approach, i.e., a combination of both pessimistic and optimistic approaches. These protocols make use of a new conflict resolution scheme called dynamic adjustment of serialization order, which supports priority-driven scheduling, and avoids unnecessary aborts.