Database Reference
In-Depth Information
Notice I used the term “documented” in the preceding paragraph. There are undocumented parameters as well.
You can identify these because their names begin with an underscore (_). There is a great deal of speculation about
these parameters. Since they are undocumented, some people believe they must be “magical,” and many people
assume that they are well known and used by Oracle insiders. In fact, I find the opposite to be true. They are not well
known and they are hardly ever used. Most of these undocumented parameters are rather boring, actually, as they
represent deprecated functionality and backward-compatibility flags. Others help in the recovery of data, not of the
database itself; for example, some of them enable the database to start up in certain extreme circumstances, but only
long enough to get data out. You have to rebuild after that.
Unless you are so directed by Oracle Support, there is no reason to have an undocumented parameter in your
configuration. Many have side effects that could be devastating. In my production database, I don't want to use any
undocumented settings.
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Use undocumented parameters only at the request of Oracle support. their use can be damaging to a
database, and their implementation can—and will—change from release to release.
Caution
You may set the various parameter values in one of two ways: either just for the current instance or persistently.
It is up to you to make sure that the parameter files contain the values you want them to. When using legacy
init.ora
parameter files, this is a manual process. To change a parameter value persistently, to have that new setting
be in place across server restarts, you must manually edit and modify the
init.ora
parameter file. With server
parameter files, you'll see that this has been more or less fully automated for you in a single command.
Legacy init.ora Parameter Files
The legacy
init.ora
file is a very simple file in terms of its construction. It is a series of variable key/value pairs. A
sample
init.ora
file might look like this:
control_files='/u01/dbfile/ORA12CR1/control01.ctl','/u02/dbfile/ORA12CR1/control02.ctl'
db_block_size=8192
db_name='ORA12CR1'
In fact, this is pretty close to the most basic
init.ora
file you could get away with in real life, though if the
block size I was using was the default on my platform (the default block size varies by platform), I could remove that
parameter. The parameter file is used at the very least to get the name of the database and the location of the
control files. The control files tell Oracle the location of every other file, so they are very important to the “bootstrap”
process that starts the instance.
Now that you know what these legacy database parameter files are and where to get more details about the valid
parameters you can set, you also need to know where to find them on disk. The naming convention for this file by
default is
init$ORACLE_SID.ora (UNIX/Linux environment variable)
init%ORACLE_SID%.ora (Windows environment variable)
and by default it will be found in
$ORACLE_HOME/dbs (UNIX/Linux)
%ORACLE_HOME%\DATABASE (Windows)
