Files - Expert Oracle Database Architecture - page 74

We'll also take a look at other types of files commonly associated with the database, such as

• Dump (DMP) files : These files are generated by the Export database utility and consumed by
the Import database utility. It should be noted that the Export utility is deprecated in current
releases of Oracle—only Import is fully supported. Import is supported to facilitate the moving
of data from older releases of Oracle (where Export was fully supported) into newer releases
of the database.

• Data Pump files : These files are generated by the Oracle Data Pump Export process and
consumed by the Data Pump Import process. This file format may also be created and
consumed by external tables.

• Flat files : These are plain old files you can view in a text editor. You normally use these for
loading data into the database.

The most important files in these lists are the data files and the redo log files, because they contain the data you
worked so hard to accumulate. I can lose any and all of the remaining files and still get to my data. If I lose my redo log
files, I may start to lose some data. If I lose my data files and all of their backups, I've definitely lost that data forever.
We will now take a look at the types of files, where they are usually located, how they are named, and what we
might expect to find in them.

Parameter Files
There are many different parameter files associated with an Oracle database, from a tnsnames.ora file on a client
workstation (used to “find” a server on the network), to a listener.ora file on the server (for the network listener
startup), to the sqlnet.ora , cman.ora , and ldap.ora files, to name a few. The most important parameter file, however,
is the database's parameter file—without this, we can't even get an instance started, as demonstrated in Chapter 2.
The remaining files are important; they are all related to networking and getting connected to the database. However,
they are beyond the scope of our discussion. For information on their configuration and setup, I refer you to the Net
Services Administrator's Guide . Since you're a developer, typically these files would be set up for you, not by you.
The parameter file for a database is commonly known as an init file, or an init.ora file. This is due to its historic
default name, which is init<ORACLE_SID>.ora . I call it “historic” because starting with Oracle9 i Release 1, a vastly
improved method of storing parameter settings for the database was introduced: the server parameter file, or simply
SPFILE . This file has the default name of spfile<ORACLE_SID>.ora . We'll take a look at both kinds of parameter files.

■ For those who are unfamiliar with the term SID or ORACLE_SID , a full definition is called for. the SID is a site
identifier . it and ORACLE_HOME (where the Oracle software is installed) are hashed together in UNiX/linux to create a
unique key name for creating or attaching a shared Global area (sGa) memory region. if your ORACLE_SID or ORACLE_
HOME is not set correctly and you are using a local (not network based) connection (see Chapter 2 for details on local/
remote connections), you'll get the ORACLE NOT AVAILABLE error, since you can't attach to a shared memory segment
that is identified by this unique key. On Windows, shared memory isn't used in the same fashion as on UNiX/linux, but the
SID is still important. You can have more than one database under the same ORACLE_HOME , so you need a way to uniquely
identify the instance associated with each one, along with their configuration files.

Note

Without a parameter file, you can't start an Oracle database. This makes the parameter file fairly important,
and as of Oracle9 i Release 2 (versions 9.2 and above), the backup and recovery tool Recovery Manager (RMAN)
recognizes this file's importance and will allow you to include the server parameter file (but not the legacy init.ora
parameter file type) in your backup set. However, since the init.ora file is simply a plain text file that you can create