Databases Reference
In-Depth Information
Of course, the database must have parallelization features to take full advantage of the
SMP architecture. Oracle operations such as query execution and other DML activity
and data loading can run as parallel processes within the Oracle server, allowing Oracle
to take advantage of the benefits of multiprocessor systems. Oracle, like all software
systems, benefits from parallel operations, as shown by “Amdahl's Law.”
Total execution time = (parallel part / number of processors) + serial part
Amdahl's Law, formulated by mainframe pioneer Gene Amdahl in 1967 to describe
performance in mixed parallel and serial workloads, clearly shows that moving an op‐
eration from the serial portion of execution to a parallel portion provides the perfor‐
mance increases expected with the use of multiple processors. In the same way, the more
serial operations that make up an application, the longer the execution time will be
because the sum of the execution time of all serial operations can offset any performance
gains realized from the use of multiple processors. In other words, you cannot speed up
a serial operation or a sequence of serial operations by adding more processors.
Each subsequent release of Oracle has added more parallelized features to speed up the
execution of queries as well as the tuning and maintenance of the database. For an
extensive list of Oracle operations that can be parallelized, see the section
“What Can
Be Parallelized?” on page 187
in
Chapter 7
.
Oracle's parallel operations take advantage of available CPU resources. If you're working
with a system on which the CPU resources are already being completely consumed, this
parallelism will not help improve performance; in fact, it could even hurt performance
by adding the increased demands for CPU power required to manage the parallel pro‐
cesses. Oracle's automatic degree of parallelism and management of consumer groups
using the Database Resource Manager can help prevent this situation.
Clustered Solutions, Grid Computing, and the Cloud
Clustered systems have provided a highly available and highly scalable solution since
initially appearing in the 1980s in a DEC VAXcluster configuration. Clusters can com‐
bine all the components of separate machines, including CPUs, memory, and I/O sub‐
systems, into a single hardware entity. However, clusters are typically built by using
shared disks linked to multiple “nodes” (computer systems). A high-speed interconnect
between systems provides a means of exchanging data and instructions without writing
to disk (see
Figure 12-2
). Each system or node runs its own copy of an operating system
and Oracle instance. Grids, described later in this chapter, are typically made up of a
few very large clusters.
