Oracle Essentials [Electronic resources] : Oracle Database 10g, 3rd Edition نسخه متنی

11.2 Uniprocessor Systems

Uniprocessor systems, like the one shown
in Figure 11-1, are the simplest systems in terms of architecture.
Each of these systems (typically a standard personal computer)
contains a single CPU and a single I/O channel and is made entirely
with industry-standard components. They are most often used as
single-user stand-alone machines; for example, for database
development or as client machines in a network. Some uniprocessor
machines are also used as small servers for databases. Versions of
this architecture made with more exotic RISC-based CPUs are typically
used as engineering, scientific, or graphics workstations today.

Figure 11-1. Typical uniprocessor system

Until the 1990s, uniprocessor systems were frequently used as servers
because of their low price and the limited ability of relational
databases to fully utilize other types of systems. However, Oracle
evolved to take advantage of systems containing multiple CPUs through
improved parallelism and more sophisticated optimization. At the same
time, the price points of Symmetric Multiprocessing (SMP) systems
(described in the next section) have plummeted dramatically, making
SMP systems the database hardware servers of choice.

Although there is only a single processor in a uniprocessor system,
the server operating systems used by these systems now support
multiple threads. Each thread can be used to support a concurrent
process, which can execute in parallel. By default, the
PARALLEL_THREADS_PER_CPU parameter in
the initialization file is set at 2 for
most platforms on which Oracle runs. Oracle can further determine the
degree of parallelism based on parameters set in the initialization
file or using the adaptive degree of parallelism feature. This
adaptive multiuser feature makes use of algorithms that take into
account the number of threads. Additional tuning parameters can also
affect parallelism. For more information about the parallel thread
capability of Oracle, see Chapter 6.