The SGA is read/write. All users connected to a multiple-process database instance
can read information contained within the instance’s SGA, and several processes write
to the SGA during execution of Oracle.
The SGA contains the following data structures:
■ Database buffer cache
■ Redo log buffer
■ Shared pool
■ Java pool
■ Large pool (optional)
■ Streams pool
■ Data dictionary cache
■ Other miscellaneous information
Part of the SGA contains general information about the state of the database and the
instance, which the background processes need to access; this is called the fixed SGA.
No user data is stored here. The SGA also includes information communicated
between processes, such as locking information.
If the system uses shared server architecture, then the request and response queues
and some contents of the PGA are in the SGA.?
sga中包含的数据库和实例状态的说明信息 , 供后台进程访问
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