Control mechanisms in distributed object bases. Synchronization, deadlock detection, migration (Univ. Passau, 1998) (Q2726310)

The dissertation addresses problems concerning the scalability and administrability of control mechanisms of distributed systems consisting of hundreds or thousands of autonomously operating databases sites. The author developed and experimentally validated new control mechanisms in this kind of distributed systems. Particularly, synchronization, deadlock detection and object migration are studied in details.NEWLINENEWLINENEWLINEIn chapter 2 the author describes the model of autonomous objects used in the thesis. It provides an appropriate framework for the developed approach. Chapter 3 presents a synchronization mechanism known widely as semantic based locking. It is shown how it can be integrated into the objects so that the serializability of their data is guaranteed. An extension of the model to transactions is also presented.NEWLINENEWLINENEWLINEDeadlock detection mechanisms are investigated in chapter 4. A new algorithm is presented and a valuable simulation study comparing the algorithm with other ones is described. The algorithm is based on dynamically creating Deadlock Detection Agents (DDA), each being responsible for detecting deadlocks in one connected component of the global Wait-For-Graph. Chapter 5 describes a prototypical, implementation of a persistent distributed system of autonomously operating objects, called AutO, which reflects requirements for distribution of database sites in wide-area environment. Besides the semantic based locking and DDA algorithm, AutO has integrated the migration concept (chapter 6). It enables objects to autonomously migrate between sites of the systems. Two possible strategies are introduced and compared through experiments with AutO. Finally, chapter 7 summarizes the thesis and gives an outline of possible future research.NEWLINENEWLINENEWLINEThe thesis provides new results. It is written in clearly style with an adequate formal approach. The associated algorithms are described in understandable way. The AutO architecture can become an inspiration for a world-wide operation enterprise.