Database Reference
In-Depth Information
msg_id='dbkrlCheckSuppressAlert:332:7003611' type='NOTIFICATION' group='startup'
level='16' host_id='localhost.localdomain' host_addr='::1'
pid='32628' version='1'>
<txt>Adjusting the default value of parameter parallel_max_servers
</txt>
</msg>
<msg time='2013-06-28T16:04:25.378-04:00' org_id='oracle' comp_id='rdbms'
msg_id='dbkrlCheckSuppressAlert:332:2000778772' type='NOTIFICATION' group='startup'
level='16' host_id='localhost.localdomain' host_addr='::1'
If you have utilities or tools to generate reports from XML (such as an Oracle database using XDB—XML DB—for
example), you may query/report on that format as well.
Of course, Enterprise Manager also displays the important alert log information as well.
Data Files
Data files, along with redo log files, are the most important type of files in the database. This is where all of your data
will ultimately be stored. Every database has at least one data file associated with it, and typically has many more
than one. Only the most simple “test” databases have one file. In fact, in Chapter 2 we saw that the simplest CREATE
DATABASE command by default created a database with three data files, listed here for reference:
NAME
-----------------------------------------------------------------------
/home/ora12cr1/app/ora12cr1/product/12.1.0/dbhome_1/dbs/dbs1ora12c.dbf
/home/ora12cr1/app/ora12cr1/product/12.1.0/dbhome_1/dbs/dbx1ora12c.dbf
/home/ora12cr1/app/ora12cr1/product/12.1.0/dbhome_1/dbs/dbu1ora12c.dbf
one for the SYSTEM tablespace (which houses the true Oracle data dictionary), and one for the SYSAUX tablespace
(where other non-dictionary objects are stored in version 10 g and above) one for the USER tablespace (tablespaces will
be explained shortly in the “Tablespaces” section). Any real database will have at least these three data files.
After a brief review of file system types, we'll discuss how Oracle organizes these files and how data is organized
within them. To understand this, you need to know what tablespaces, segments, extents, and blocks are. These are the
units of allocation that Oracle uses to hold objects in the database, and I describe them in detail shortly.
A Brief Review of File System Mechanisms
There are four file system mechanisms (only three in Oracle 12c) in which to store your data in Oracle. By your data,
I mean your data dictionary, redo, undo, tables, indexes, LOBs, and so on—the data you personally care about at the
end of the day. Briefly, they are
“Cooked” operating system (OS) file systems : These are files that appear in the file system just
like your word processing documents do. You can see them in Windows Explorer; you can
see them in UNIX/Linux as the result of an ls command. You can use simple OS utilities
such as xcopy on Windows or cp on UNIX/Linux to move them around. Cooked OS files
are historically the most popular method for storing data in Oracle, but I see that changing
with the introduction of ASM (more on that in a moment). Cooked file systems are typically
buffered as well, meaning that the OS will cache information for you as you read and, in some
cases, write to disk.
 
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