SGA Components

The SGA has several components, as listed in the following table. Oracle Database XE automatically tunes the individual sizes of these components for optimal performance.

Component	Description
Buffer cache	The buffer cache is the component of the SGA that acts as the buffer to store any data being queried or modified. All clients connected to the database share access to the buffer cache. The buffer cache helps avoid repeated access from the physical disk, a time-consuming operation.
Shared pool	The shared pool caches operational information and code that can be shared among users. For example: SQL statements are cached so that they can be reused. Information from the data dictionary, such as user account data, table and index descriptions, and privileges, is cached for quick access and reusability. Stored procedures are cached for faster access.
Redo log buffer	The redo log buffer improves performance by caching redo information (used for instance recovery) until it can be written at once and at a more opportune time to the physical redo log files that are stored on disk. Redo information and redo log files are discussed in "Online Redo Log Files".
Large pool	The large pool is an optional area that is used for buffering large I/O requests for various server processes.