Databases Reference
In-Depth Information
Log Writer (LGWR)
The Log Writer process writes the buffers in the SGA's redo log buffer out to disk
to the redo log files. The Log Writer process must be able to write redo log buff-
ers fast enough to make sure that there is room in the redo log buffer for entries
from new transactions. By writing all changes to the database to the redo log
files, the changes made to the database can be recovered by reissuing the com-
mands in the logs if an instance failure occurs.
Log Writer writes under a variety of conditions: when a user issues a COMMIT,
when the redo log buffer is one-third full, when DBWn writes dirty buffers, or
every three seconds.
System Monitor (SMON)
SMON performs a number of different functions in the database. If there is a sys-
tem crash, the SMON process will apply the changes in the redo log files (saved
to disk previously by the LGWR process) to the datafiles the next time the
instance is started. This ensures that no committed transactions are lost because
of the system crash. (SMON also performs a number of other tasks that are
beyond the scope of this topic.)
Installing Oracle Software
Now that you have an understanding of how the Oracle database components
are structured and interoperate, you can install the software that will create and
control the components.
Oracle Universal Installer (OUI)
A GUI-based tool used to install or uninstall
Oracle software components and tools.
To install Oracle 10
g
, you can use the
Oracle Universal Installer (OUI)
, a GUI-
based Java tool that has the same look and feel regardless of which software plat-
form you are using to install the software. As part of most Oracle installations, you
can also install the
Oracle Enterprise Manager (OEM)
toolset, which is a graphical
system management tool that allows a DBA to manage and administer more than
one Oracle instance from a single application. In addition, the browser-based
Oracle Enterprise Manager Database Control
interface makes it easy to adminis-
ter an Oracle database from any platform that supports a web browser.
Here, we'll go through a basic installation of the Oracle server and review
some of the key features of the OEM console.
Oracle Enterprise Manager (OEM)
A GUI-based tool used to manage one or
more Oracle database instances.
Using the Oracle Universal Installer
One of the key concepts to understand when Oracle is installed on a server is the
Oracle Home
. An Oracle Home is simply a single directory location in the file-
system that contains all of the installed Oracle products and options for a specific
version of the Oracle software. Each Oracle Home has a name assigned to it, and
the value of this name is stored in the Windows Registry.
Oracle Enterprise Manager
Database Control
An Internet browser-based tool used to
manage one or more Oracle database
instances.
