Database Reference
In-Depth Information
Redo Log Files & Archived Redo Log Files:
Redo Log files are the files that maintain the changes happening
in data. To visualize this keep Microsoft Word in mind, it also
keeps the changes you make in data so that you can revert back
as required. Every Oracle Database has set of two or more redo
log files. Each set is called redo log file group.
Redo log files
gets utilized in a circular fashion
i.e. when Oracle Instance
finishes writing the last redo log file then it starts overwriting the
first one unless you archived that redo log file or in other words
unless you order Oracle Instance (Giene) to make sure redo log
files gets archived before they get over written. We will study
this topic in great detail in the last article of this chapter.
The way we can protect overwriting of Redo Log files is to run
the Oracle Instance in Archive Log Mode. If Oracle is running in
this mode than redo log files will get archived to the destination
you specify in the parameter file before getting overwritten.
Parameter File (PFILE):
Parameter file contains the name of the database, location of
control file, memory structure of Oracle Instance and certain
other necessary Oracle system configuration parameters. PFILE
is read by Oracle Instance while starting up the database or even
before that i.e. when the Instance creates itself.
We will talk about instance in the next chapter but let me give
you a brief image what instance is.
The background processes
and memory architecture constitute an instance.
You may find it
difficult to understand it at this spot. Do not stop. Keep reading
and everything will be fine. Since Instance is the combination of
“Memory Architecture” and “Background Processes” so when
you double click oracle icon or runs oracle system, the first thing
that gets erected is Oracle Instance. How the memory structure
would be for that instance, that's what we define in parameter
file.
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