Characteristics of distributed database systems: 1. Independent transparency, users do not need to care about the logical partition of data, and do not need to care about the details of the physical location distribution of data; 2. Centralized node integration; 3. Replication transparency, users do not need to Pay attention to the replication status of the database in each node in the network, and the update of the replicated data is automatically completed by the system; 4. Easy to expand.
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
Distributed database system (DDBS) includes distributed database management system (DDBMS) and distributed database (DDB). In a distributed database system, an application can transparently operate the database. The data in the database are stored in different local databases, managed by different DBMSs, run on different machines, and supported by different operating systems. , are connected together by different communication networks.
Characteristics of distributed database systems
1. Independent transparency (distribution transparency)
Data independence is one of the main goals pursued by the database method. Distribution transparency means that users do not need to care about the logical partition of the data, the details of the physical location distribution of the data, and the consistency of duplicate copies (redundant data). , and at the same time, you don’t have to worry about which data model is supported by the database on the local site. The advantages of distribution transparency are obvious. With distribution transparency, user applications can be written as if the data were not distributed. Applications do not have to be rewritten when data is moved from one site to another. When adding duplicate copies of certain data, there is no need to rewrite the application program. Data distribution information is stored in the data dictionary by the system, and user access requests for non-local data are interpreted, converted, and transmitted by the system based on the data dictionary.
2. Centralized node combination
The database is a resource shared by users. In a centralized database, in order to ensure the security and integrity of the database, the shared The control of the database is centralized, and a DBA is responsible for supervising and maintaining the normal operation of the system. In a distributed database, there are two levels of data sharing:
The first is local sharing, that is, the shared data of each user on the local site is stored in the local database. These data are commonly used by users at the local site.
The second is global sharing, that is, each site of the distributed database also stores data that can be shared by users in other sites on the network to support global applications in the system.
3. Replication Transparency
Users do not need to care about the replication of the database at each node in the network, and the update of the replicated data is automatically completed by the system. In a distributed database system, data from one site can be copied to other sites for storage. Applications can use the copied data to complete distributed operations locally, avoiding data transmission through the network and improving system operation and query efficiency. However, the update operation of replicated data involves updating all replicated data.
4. Ease of scalability
In most network environments, a single database server will eventually become unsatisfactory. If the server software supports transparent horizontal scaling, then multiple servers can be added to further distribute data and share processing tasks.
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