Most SQL statements affect the current instance. You can use SQL*Plus to start and stop instances in the Oracle RAC database. You do not need to run SQL*Plus commands as root on Linux and UNIX systems or as Administrator on Windows systems. You need only the proper database account with the privileges that you normally use for a noncluster Oracle database. Some examples of how SQL*Plus commands affect instances are:
ALTER SYSTEM CHECKPOINT LOCAL affects only the instance to which you are currently connected, rather than the default instance or all instances.
ALTER SYSTEM CHECKPOINT or ALTER SYSTEM CHECKPOINT GLOBAL affects all instances in the cluster database.
ALTER SYSTEM SWITCH LOGFILE affects only the current instance.
To force a global log switch, use the ALTER SYSTEM ARCHIVE LOG CURRENT statement.
The INSTANCE option of ALTER SYSTEM ARCHIVE LOG enables you to archive each online redo log file for a specific instance.
Table 3-1 describes how SQL*Plus commands affect instances.
Table 3-1 How SQL*Plus Commands Affect Instances
Always affects the current instance.
Affects the default instance if no instance is specified in the CONNECT command.
Affects the node running the SQL*Plus session, regardless of the location of the current and default instances.
Does not affect any particular instance, but rather the database.
Displays information about the current instance, which can be different from the default local instance if you have redirected your commands to a remote instance.
Displays parameter and SGA information from the current instance.
Always affects the current instance. These are privileged SQL*Plus commands.