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person using the machine at a time. A typical multiuser system, on the other
hand, has more disks and more memory and may have multiple processors. It
serves a large number of users who are connected to the system remotely.
Database systems designed for use by single users usually do not provide
many of the facilities that a multiuser database provides. In particular, they may
not support concurrency control, which is not required when only a single user
can generate updates. Provisions for crash recovery in such systems are either
absent or primitive—for example, they may consist of simply making a backup
of the database before any update. Some such systems do not support SQL, and
they provide a simpler query language, such as a variant of QBE. In contrast,
database systems designed for multiuser systems support the full transactional
features that we have studied earlier.
Although most general-purpose computer systems in use today have multiple
processors, they have coarse-granularity parallelism, with only a few processors
(about two to four, typically), all sharing the main memory. Databases running
on such machines usually do not attempt to partition a single query among the
processors; instead, they run each query on a single processor, allowing multiple
queries to run concurrently. Thus, such systems support a higher throughput;
that is, they allow a greater number of transactions to run per second, although
inpidual transactions do not run any faster.
Databases designed for single-processor machines already provide multitasking,
allowing multiple processes to run on the same processor in a time-shared
manner, giving a view to the user of multiple processes running in parallel. Thus,
coarse-granularity parallel machines logically appear to be identical to singleprocessor
machines, and database systems designed for time-shared machines
can be easily adapted to run on them.
In contrast, machines with fine-granularity parallelism have a large number
of processors, and database systems running on such machines attempt to
parallelize single tasks (queries, for example) submitted by users. We study the
architecture of parallel database systems in Section 17.3.
Parallelism is emerging as a critical issue in the future design of database
systems. Whereas today those computer systems with multicore processors have
only a few cores, future processors will have large numbers of cores.1 As a result,
parallel database systems, which once were specialized systems running on
specially designed hardware, will become the norm.
B.原文的翻译
数据库系统架构
数据库系统的体系结构在很大程度上是通过底层的影响在其上运行，尤其是通过计算机对这些方面的计算机系统架构网络，并行和分布：
•计算机联网允许一些任务要在服务器系统上执行和一些任务来在客户端系统 上执行。这项工作有分工导致客户端 - 服务器的数据库系统。论文网
•计算机系统内并行处理允许数据库系统活动要加快，从而允许交易更快的响应，以及更每秒事务。查询可以在它利用了一种方式来处理并行底层计算机系统提供。需要对平行查询处理导致了并行数据库系统。