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

A distributed file service based on optimistic concurrency control

The design of a layered file service for the Amoeba Distributed System is discussed, on top of which various applications can easily be intplemented. The bottom layer is formed by the Amoeba Block Services, responsible for implementing stable storage and repficated, highly available disk blocks. The next layer is formed by the Amoeba File Service which provides version management and concurrency control for tree-structured files. On top of this layer, the appficafions, ranging from databases to source code control systems, determine the structure of the file trees and provide an interface to the users

Protocols for Integrity Constraint Checking in Federated Databases

A federated database is comprised of multiple interconnected database systems that primarily operate independently but cooperate to a certain extent. Global integrity constraints can be very useful in federated databases, but the lack of global queries, global transaction mechanisms, and global concurrency control renders traditional constraint management techniques inapplicable. This paper presents a threefold contribution to integrity constraint checking in federated databases: (1) The problem of constraint checking in a federated database environment is clearly formulated. (2) A family of protocols for constraint checking is presented. (3) The differences across protocols in the family are analyzed with respect to system requirements, properties guaranteed by the protocols, and processing and communication costs. Thus, our work yields a suite of options from which a protocol can be chosen to suit the system capabilities and integrity requirements of a particular federated database environment

H2O: An Autonomic, Resource-Aware Distributed Database System

This paper presents the design of an autonomic, resource-aware distributed database which enables data to be backed up and shared without complex manual administration. The database, H2O, is designed to make use of unused resources on workstation machines. Creating and maintaining highly-available, replicated database systems can be difficult for untrained users, and costly for IT departments. H2O reduces the need for manual administration by autonomically replicating data and load-balancing across machines in an enterprise. Provisioning hardware to run a database system can be unnecessarily costly as most organizations already possess large quantities of idle resources in workstation machines. H2O is designed to utilize this unused capacity by using resource availability information to place data and plan queries over workstation machines that are already being used for other tasks. This paper discusses the requirements for such a system and presents the design and implementation of H2O.Comment: Presented at SICSA PhD Conference 2010 (http://www.sicsaconf.org/

Schema architecture and their relationships to transaction processing in distributed database systems

We discuss the different types of schema architectures which could be supported by distributed database systems, making a clear distinction between logical, physical, and federated distribution. We elaborate on the additional mapping information required in architecture based on logical distribution in order to support retrieval as well as update operations. We illustrate the problems in schema integration and data integration in multidatabase systems and discuss their impact on query processing. Finally, we discuss different issues relevant to the cooperation (or noncooperation) of local database systems in a heterogeneous multidatabase system and their relationship to the schema architecture and transaction processing

Online Collaborative Editor

“Online collaborative editor” is a node.js based browser application that provides real time collaborative editing of files and improves pair programming. Current real time editors fail to provide simultaneous viewing and editing of files within the server and results in a complex version controlling system. Such systems are also vulnerable to deadlocks and race conditions. This project provides a platform for real time collaborative editors, which can support simultaneous editing and viewing of files and handle concurrency problems by using locking mechanism. The experiment results showed that node.js platform provides good performance for collaborative editing