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Until Oracle 8i DBAs have been using a text file called the pfile (parameter file) to store the database initialization parameters. ---8i之前使用文本参数文件
The pfile is read at instance startup time to get specific instance characteristics. Any changes made the pfile would only take effect when the database is restarted.
However, parameters that were dynamically alterable could be changed using the appropriate ALTER SYSTEM or ALTER SESSION statement, which would take effect immediately.
As of Oracle9i, new feature called the spfile (server parameter file). The spfile is a binary file that contains the same information as the old pfile. --9i开始引入和服务参数文件，二进制类型
The spfile is a server-side initialization parameter file; parameters stored in this file are persistent across database startups.
This makes all the changes made to the instance using the ALTER SYSTEM statement persistent. Oracle requires that you start an instance for the first time using the pfile and then create the spfile.
The server parameter file (also called SPFILE) is in a single location where all the necessary parameters are defined and stored. The defined parameter values are applicable for all the instances in the cluster.
The SPFILE permits dynamic changes without requiring you to bring down the instance.
You can still use the client side parameter file to manage parameter settings in Real Application Clusters; however, administrative convenience is sacrificed and the advantage of dynamic change is lost.
By default, if you do not specify PFILE in your STARTUP command, Oracle will use a server parameter file. ---数据库启动的时候默认使用spfile
SERVER PARAMETER FILE ( SPFILE ) ---服务参数文件
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A server parameter file is basically a repository for initialization parameters.
Initialization parameters stored in a SPFILE are persistent, meaning any parameter changes made while an instance is running can persist across instance shutdown and startup.
In this way, all the initialization parameters manually updated by ALTER SYSTEM SET commands become persistent.
It also provides a basis for the Oracle database server to self-tune.
Another advantage, particularly for multi-instance RAC systems, is that a single copy of the parameter file can be used by all instances. Even though a single file is used to specify parameters, it has different format styles to support both the common values for all instances, as well as the specific values for an individual instance.
A server parameter file is initially built from the traditional text initialization parameter file, using the create SPFILE statement. It is a binary file that cannot be browsed or edited with a text editor.
Oracle provides other interfaces for viewing and modifying parameter settings. At system startup, the default behavior of the STARTUP command is to read a SPFILE to obtain initialization parameter settings. If the STARTUP command doesn't have a PFILE clause, it reads the SPFILE from a location
specified by the operating system.
If you choose to use the traditional text initialization parameter file, you must specify the PFILE clause when issuing the STARTUP command.
SETTING THE SERVER PARAMETER FILE VALUES ---设置参数文件的values
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Use the SID designator to set instance-specific parameter values in the server parameter file.
For settings across the database, use a '*', and for a specific instance, set the prefix with SID a