畢業(yè)設計(論文)外文翻譯----分布式dbms的概念與設計-其他專業(yè)(編輯修改稿)
2025-02-24 05:04 本頁面
【文章內(nèi)容簡介】 As data may be replicated so that it exists at more than one site, the failure of a node or a munication link does not necessarily make the data inaccessible. Improved performance As the data is located near the site of ‘greatest demand’, and given the inherent parallelism of distributed DBMSs, speed of database access may be better than that achievable form a remote centralized database. Furthermore, since each site handles only a part of the entire database, there may not be the same contention for CPU and I/O services as characterized by a centralized DBMS. Economics In the 1960s,puting power was calculated according to the square of the costs of the equipment: three times the cost would provide nine times the power. This was known as Grouch’s Law. However, it is now generally accepted that it costs much less to create a system of smaller puters with the equivalent power of a single large puter. This makes it more costeffective for corporate divisions and departments to obtain separate puters. It is also much more costeffective to add workstations to a work than to update a mainframe system. The second potential cost saving occurs where databases are geographically remote and the applications require access to distributed data. In such cases, owing to the relative expense of data being transmitted across the work as opposed to the cost of local access, it may be much more economical to partition the application and perform the processing locally at each site. Modular growth In a distributed environment, it is much easier to handle expansion. New sites can be added to the work without affecting the operations of other sites. This flexibility allows an anization to expand relatively easily. Increasing database size can usually be handled by adding processing and storage power to the work. In a centralized DBMS, a growth may 4 entail changes to both hardware and software. Complexity A distributed DBMS that hides the distributed nature form the user and provides an acceptable level of performance, reliability is inherently more plex than a centralized DBMS. The fact that data replication adequately, there will be degradation in availability, reliability, and performance pared with the centralized system, and the advantages we cited above will bee disvantages. Cost Increased plexity means that we can expect the procurement and maintenance costs for a DDBMS to be higher than those for a centralized DBMS. Furthermore, a distributed DBMS requires additional hardware to establish a work between sites. These are ongoing munication costs incurred with the use of this work. There are also additional labor costs to manage and maintain the local DBMSs and t
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