IBIS system is an extensive and complex project and changes in its source code is quiet challenging. To make an adaptation of Theta replication method easier for IBIS system a special interface is implemented. This interface is realized by extending IBIS database management class for handling data replication man-agement.
Figure 5.20: Listing for inserting web object – centralized database
The replication interface created on the IBIS purposes allows on extremely straightforward adaptation of Theta replication method in IBIS. As it is presented in 5.3.4 data management for centralized database is realized through iBATIS framework. Listing presented in fig. 5.20 provides an example of inserting new Web Object to centralized database. Parameters of object WobObject are used during data insertion into database. The same parameters are used for creation of strings containing the set of parameters as it is shown in fig. 5.21. The implemented replication interface allows to submit such prepared strings to the middleware, and in consequence appropriate procedures are executed in replicas.
Figure 5.21: Listing for inserting web object – replicated database
5.5 Summary
Implementation of multi-agent IBIS system using presented Theta replication method satisfies the requirements of efficient Internet scanning process realized in the system. Strategy Management process evaluation confirms the high scala-bility of the replication method in the real life replication process. Adding new replicas into the IBIS system causes that performance of the replication man-agement process lowers slightly, while on the other hand the overall efficiency of the activities realized in the system grows significantly allowing to provide ser-vice with greater amount of agents working at the same time (Cluster Supervisor Agents and related Working Agents). Replicated system can handle more concur-rent sessions from agents, allowing on invocation of thousands of simultaneously
running Cluster Supervisor Agents. Performed failure resistance tests in the real life system confirm the replicated system operates properly and is resistant to failures.
Data replication based on Theta replication method allows to preserve previ-ously implemented functionalities, while on the other hand allows to adapt easily Theta method to the requirements of the data replication in IBIS, without the necessity of performing changes in the core of the implemented system.
Higher distances between remote replicas and lowered speed of network in-terfaces cause the response times of the replicated system are expected to grow.
However, in the system with Theta method implemented these response times are expected to grow slowly since the amount of the communicates exchanged between remote locations is reduced considerably (confirmation of the commit from the remote replicas is not sent). Appropriate tests, however, are not yet performed because of the short distances between particular replicas in current IBIS implementation, which cause considerable network delays do not appear in IBIS related infrastructure.
Conclusions
Theta replication method has been designed for the high availability multi-tier architecture with distributed middleware. The middleware uses its own concur-rency control mechanism, called Conflict Prevention algorithm, which enables transactions to be executed with a degree of parallelism. Conflict Prevention algorithm defines transaction processing order in a way that ensures nonconflict-ing processnonconflict-ing. Moreover, it supports execution of transaction with a degree of parallelism, while at the same time guarantees data consistency in replicas (the same results of processed transactions in each replica). Since Conflict Prevention algorithm ensures that conflict can not happen in any replica, which technically is a single database instance, transactions are applied to the system in a way as they would be applied in a system with centralized database. As a result us-age of distributed data locks for such data replication is not required, which is confirmed within the tests performed for both implementations of the replication system based on Theta method.
In laboratory experimental evaluation of Theta replication control method shows that Theta method provides scalable and non-conflicting mechanism to keep multiple replicas synchronized. The method ensures high scalability and at the same time provides acceptable efficiency of data replication. Theta approach is suitable for heterogeneous environments which is implied as a possibility of replication implementation in environments with different RDBMS, OS and/or platforms without the necessity of using complex gateways, additional drivers, etc. The replication system is compatible with the most of existing database
sys-Data replication based on Theta method allows to preserve previously imple-mented functionalities of IBIS system, while on the other hand allows to adapt easily the method to the requirements of the data replication in IBIS without the necessity of performing changes in the core of the implemented system.
Implementation of the multi-agent IBIS system based on Theta replication method satisfies the requirements of the Internet monitoring realized in the sys-tem. Adding more replicas to the system causes its performance lowers slightly in comparison to the configuration with only two database copies, which allows to provide service with more concurrently working agents and in consequence significantly improves overall system processing performance. Performed fault tolerance evaluation of the IBIS system with replication confirms resistance to failures of Theta method.
In the author’s opinion the most important achievements of this dissertation are:
• Design of the new data replication method for transactional, multi-node, distributed systems.
• Implementation of the method both in the laboratory environment and on the purpose of information sharing in the operative multi-agent IBIS system.
• Performing wide-ranging positive tests of the proposed method.
Theta replication method has been designed, implemented and evaluated both in in-laboratory environment and in the real life multi-agent IBIS system. Repli-cation software built for the purposes of these implementations can be used for data replication in the systems which need to share data between remote loca-tions. However, additional work is required to be done to make the software usage in the future implementations easier. The following list presents tasks that are planned to be performed in the future:
interfaces).
• Implementation of the universal connection handler that can be used for the majority of the available relational database management systems (until now Theta replication method has been implemented and tested for the limited amount of relational database management systems).
• Packaging the software and preparation of the universal installer to provide easy deployment method of the software as well as the replication configu-ration.
• Preparation of the web-based repository for binaries and source codes which will act as a centralized location for software packages connected with Theta replication method, and which can be used by software developers to control and manage software releases.