Measure the test taker's understanding about the advantages and disadvantages of the distributed database system.

The distributed database system is developed on the basis of the centralized database system. Compared with the distributed database system and the centralized database system, it can be found that the distributed database system has the following advantages:

(1) more suitable for Distributed Management and Control. The structure of the distributed database system is more suitable for organizations or organizations with geographical distribution. It allows different departments in different regions to implement local control over their own data. For example, global data is input, queried, and maintained locally. In this case, because computer resources are close to users, the communication cost can be reduced and the response speed can be improved, while only a small amount of data is involved in other site databases, this greatly reduces the amount of information transmitted over the network, and improves the security of local data.

(2) flexible architecture. Centralized database systems emphasize centralized control. Physical databases are stored on one site and managed centrally by a DBMS. Multiple users can only run the DBMS with the support of multiple user operating systems through short-range or remote terminals to share data in the database. However, the autonomy of the local DBMS in the distributed database system enables most local transaction management and control to be implemented in the local environment, you must use the network as a global transaction to manage data that involves other sites. Distributed DBMS can be designed to have different levels of autonomy, from full field autonomy to almost completely centralized control.

(3) The system is cost-effective, with high reliability and good availability. Compared with a large computer supporting a large Jizhong database, the database adds some processes and remote terminals, distributed Database systems supported by super micro computers or super small computers often have higher cost effectiveness and implementation flexibility. Distributed Systems have higher reliability and higher availability than centralized systems. If data is distributed in multiple sites and many copies of data exist, failure of individual sites or communication links will not cause the system to crash, in addition, local system faults do not cause global loss of control.

(4) accelerated response under certain conditions. If the accessed data is stored in the local database, it can be executed by the user's computer, and the speed will be faster.

(5) good scalability, easy to integrate with existing systems, and easy to expand.

For an enterprise or organization, the distributed database technology can be used to develop global applications based on a number of databases created, and some changes can be made to the original local database system to form a distributed system. This makes it easy to build a large database system, saving both time and money and material resources. You can also quickly expand the existing distributed database system by increasing the number of sites.

Disadvantages of Distributed Database Systems

Distributed Database systems have the following Disadvantages:

(1) high communication overhead and high failure rate. For example, when the network communication transmission speed is not high, the system response speed is slow. factors related to communication counties often lead to system faults, and the complexity of the system may also lead to a high failure rate. After a fault occurs, the system recovery is complex and the reliability needs to be improved.

(2) the data access structure is complex. Generally, accessing data in a database during distribution is more complex and overhead than accessing data in a centralized database.

(3) data security and confidentiality are difficult to control. When the database has a high degree of venue autonomy, the local database administrators of different venues can adopt different security measures, but the global data cannot be ensured to be safe. Security issues inherent in distributed systems. Because distributed systems implement distributed control through communication networks, the communication networks themselves have weaknesses in protecting data security and confidentiality, and data can be easily stolen.

Distributed Database Design, SITE division, and data distribution across different sites are complex. Data Division and distribution have a great impact on system performance, response speed, and availability. The communication speed of different sites is much slower than the access speed of access components of local database systems. The communication system has a high latency, And it is costly to Process Communication Information on the CPU. In a distributed database system, you must pay attention to the design, query processing and optimization, transaction management, concurrency control, and Directory management of distributed databases.

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