Comparing two-phase locking and optimistic concurrency control protocols in multiprocessor real-time databases

Previous studies (Haritsa et al., 1990) have shown that optimistic concurrency control (OCC) generally performs better than lock-based protocols in disk-based real-time database systems (RTDBS). We compare the two concurrency control protocols in both disk-based and memory-resident multiprocessor RTDBS. Based on their performance characteristics, a new lock-based protocol, called two phase locking-lock write all (2PL-LW), is proposed. The results of our performance evaluation experiments show that different characteristics of the two environments indeed have great impact on the protocols' performance. We identify such system characteristics and show that our new lock-based protocols, 2PL-LW, is better than OCC in meeting transaction deadlines in both disk-based and memory-resident RTDBS.published_or_final_versio

Performance analysis of a real-time database with optimistic concurrency control

For a real-time shared-memory database with Optimistic Concurrency Control (OCC), an approximation for the transaction response-time distribution and thus for the deadline miss probability is obtained. Transactions arrive at the database according to a Poisson process. There is a limited number of CPUs that can handle transactions in parallel. TransactIons have soft deadlines, and the probability of data conflicts is equal for all transactions. The response time of a transaction consists of possible waiting time (if at arrival all CPUs are occupied) plus a number of execution runs (due to the occurrence of conflicts). In this study, we analyze the case where the execution time of all transactions is constant. Although in practice execution times are never really constant, it is important to analyze this simplifying constant case first, before trying to analyze more general execution-time distributions. We model the real-time database (RTDB) with OCC by a multi-server queueing system with a very special kind of feedback. The probability that a transaction is fed back for a rerun depends on the number of transactions that has committed during its execution. Numerical experiments, which compare the approximative analysis with simulation, show that the analysis provides a good and very fast approximation for the response-time distribution and thus for the percentage of transactions that meets its deadline. We also discuss how the model and the analysis can be extended such that more realistic assumptions, e.g. non-uniform data access, several transaction types, and general execution-time distributions, can be handled

Self-adjusting multi-granularity locking protocol for object-oriented databases

Object-oriented databases have the potential to be used for data-intensive, multi-user applications that are not well served by traditional applications. Despite the fact that there has been extensive research done for relational databases in the area of concurrency control; many of the approaches are not suitable for the complex data model of object-oriented databases. This thesis presents a self-adjusting multi-granularity locking protocol (SAML) which facilitates choosing an appropriate locking granule according to the requirements of the transactions and encompasses less overhead and provides better concurrency compared to some of the existing protocols. Though there has been another adaptive multi-granularity protocol called AMGL [1] which provides the same degree of concurrency as SAML: SAML has been proven to have significantly reduced the number of locks and hence the locking overhead compared to AMGL. Experimental results show that SAML performs the best when the workload is high in the system and transactions are long-lived

Priority-based speculative locking protocols for distributed real-time database systems.

With globalization, multinational networked organizations' need for exchange of information has led to the emergence of applications that are heavily dependent on globally distributed and constantly changing data. Such applications include, stock trading, Computer Aided Design and Manufacturing (CAD/CAM), online reservation systems, telecommunication systems, e-commerce systems and real time navigation systems. These applications introduce the need for distributed real time database systems (DRTDBS) which must access/manipulate data spread over a network in addition to meeting the real time constraints and maintaining database consistency. In order to improve performance within DRTDBS, attention needs to be given to concurrency control mechanism and transaction's time constraints. A number of protocols have been suggested in recent years to address these issues. One of the proposed protocols, Speculative Locking (SL), has especially demonstrated the capability of improving performance within Distributed Database System by allowing parallelism between conflicting transactions without violating serializability. This research extends SL by giving it the capability of taking a transaction's priority into consideration when scheduling transactions. In addition, a nested transaction model is used to access the data that is distributed across the network. We propose two new Priority-based Speculative Locking protocols: (1) Preemptive Speculative Locking (PSL) and (2) Priority inheritance Speculative Locking (PiSL). PSL extends SL by allowing any incoming higher priority transaction to preempt and abort any lower priority transaction in case of lock conflict thus giving the higher priority transaction a chance to meet the deadline. PiSL, on the other hand, attempts to prevent any wasted work by avoiding preemption by a higher priority transaction. Instead, the lower priority transaction inherits the priority of the blocked transaction. This gives both transactions an opportunity to meet their deadline whenever possible.The original print copy of this thesis may be available here: http://wizard.unbc.ca/record=b159863