-
Database-System Architectures The architecture of a database system is greatly influenced by the underlying computer system on which it runs, in particular by such aspects of computer architecture as networking, parallelism, and distribution:39689
- 上一篇：JSP的基础课程学习英文文献和中文翻译
- 下一篇：ASP.NET概述英文文献和中文翻译
• Networking of computers allows some tasks to be executed on a server system and some tasks to be executed on client systems. This pision of work has
led to client–server database systems.
• Parallel processing within a computer system allows database-system activities
to be speeded up, allowing faster response to transactions, as well as more
transactions per second. Queries can be processed in a way that exploits the
parallelism offered by the underlying computer system. The need for parallel
query processing has led to parallel database systems.
• Distributing data across sites in an organization allows those data to reside
where they are generated or most needed, but still to be accessible from other
sites and from other departments. Keeping multiple copies of the database
across different sites also allows large organizations to continue their database
operations even when one site is affected by a natural disaster, such as flood,
fire, or earthquake. Distributed database systems handle geographically or ad-
ministratively distributed data spread across multiple database systems.
We study the architecture of database systems in this chapter, starting with
the traditional centralized systems, and covering client–server, parallel, and distributed
database systems.
Centralized and Client–Server Architectures
Centralized database systems are those that run on a single computer system
and do not interact with other computer systems. Such database systems span
a range from single-user database systems running on personal computers to
high-performance database systems running on high-end server systems. Client
–server systems, on the other hand, have functionality split between a server
system and multiple client systems.
Centralized Systems
A modern, general-purpose computer system consists of one to a few processors
and a number of device controllers that are connected through a common bus that
provides access to shared memory . The processors have local cache
memories that store local copies of parts of the memory, to speed up access to data.
Each processor may have several independent cores, each of which can execute
a separate instruction stream. Each device controller is in charge of a specific
type of device (for example, a disk drive, an audio device, or a video display).
The processors and the device controllers can execute concurrently, competing
for memory access. Cache memory reduces the contention for memory access,
since it reduces the number of times that the processor needs to access the shared
memory.
We distinguish two ways in which computers are used: as single-user systems
and as multiuser systems. Personal computers and workstations fall into the first
category. A typical single-user system is a desktop unit used by a single person,
usually with only one processor and one or two hard disks, and usually only one