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

11.1 System Basics

Any discussion of hardware systems
begins with a review of the components that make up a hardware
platform and the impact these components have on the overall system.
You'll find the same essential components under the
covers of any computer system:

One or more CPUs, which execute the basic instructions that make up
computer programs

Memory, which stores recently accessed instructions and data

An input/output (I/O) system, which typically consists of some
combination of a disk, a diskette, and tape controllers for pulling
data and programs off physical media or network controllers for
connecting the system to other systems on the network.

The number of each of these components and the capabilities of the
individual components themselves determine the ultimate cost and
scalability of a system. A machine with four processors is typically
more expensive and capable of doing more work than a single-processor
machine; new versions of components, such as CPU chips, are typically
faster and more expensive than older versions.

Typically, in the fast moving world of chip development, computers with a smaller number of processors are able to integrate new chips more rapidly than machines with larger numbers of CPUs.

In decision-support or data warehousing systems, CPU and memory are
often the performance-limiting components. In online transaction
processing (OLTP) systems, I/O is often the most critical component.

Each component has a latency cost and capacity associated with it.
The latency cost of a
component is the amount of latency the use of that component
introduces into the systemin other words, how much slower each
successive level of a component is than its previous level (e.g.,
Level 2 versus Level 1; see Table 11-1).

The CPU and the Level 1 (L1) memory cache on the CPU have the lowest
latency, as shown in Table 11-1, but also the least capacity. Disk
has the most capacity but the highest latency.

There are several different types of memory: an L1 cache, which is on the CPU chip; an L2 (Level 2) cache, which is on the same board as the CPU; and main memory, which is the remaining memory on the machine.

An important part of tuning any Oracle database involves
reducing the need to read data from sources with the greatest latency
(e.g. disk) and, when a disk must be accessed, ensuring that there
are as few bottlenecks as possible in the I/O subsystem. As a program
(or the Oracle database a program uses) accesses a greater percentage
of its data from memory rather than disk, the overall latency of the
system is correspondingly decreased. For more information about some
of these tuning issues, see Chapter 6.