OPTIMISTIC CONCURRENCY-CONTROL PROTOCOL FOR REAL-TIME DATABASES

In recent years, the use of optimistic schemes for concurrency control in real-time database systems (RTDBS) has received more and more atte ntion. Different real-time optimistic protocols have been proposed. Th ey incorporate different priority conflict resolution methods into the validation phase of a transaction to give preferences for the commitm ent of higher priority transactions. However, some of these protocols suffer from the problem of heavy restart overheads. Restarting near-to -complete transactions greatly increases the system workload and the d eadline missing probability of the transactions (Haritsa et al., 1992; Huang, 1991). In order to reduce the number of restarts, dynamic adju stment of the serialization order of the conflicting transactions has been suggested using timestamp intervals to record the transactions' s erialization constraints (Lee and Son, 1993a, 1993b; Lee, 1994). Howev er, these kinds of protocols have the problem of heavy implementation overheads as the timestamp intervals have to be checked and updated in case of any conflict even though the transactions are still in their read phases (Lee, 1994). In this paper, we propose a new real-time opt imistic protocol which employs the notion of dynamic adjustment of ser ialization order by backward-adjusting the non-serious conflicting tra nsactions before the committing transactions so that many restarts can be eliminated. In the protocol, the overhead to support dynamic adjus tment of serialization order is small. All checking is performed at th e validation test of a transaction so as to provide more freedom for t he adjustments. No conflict and serialization constraints have to be r ecorded during the read phase of a transaction. Performance studies of the proposed protocol by varying different parameters indicate that i t outperforms other protocols. (C) 1997 by Elsevier Science Inc.