Tài liệu Sybex OCA Oracle 10g Administration I Study Guide phần 2

Oracle uses a least recently used (LRU) algorithm to manage the contents of the Shared Pool
and Database Buffer Cache. When a user’s Server Process needs to put a SQL statement into the
Shared Pool or copy a database block into the Buffer Cache, Oracle uses the space in memory
that is occupied by the least recently accessed SQL statement or buffer to hold the requested
SQL or block copy. Using this technique, Oracle keeps frequently accessed SQL statements and
database buffers in memory longer, improving the overall performance of the server by minimizing
parsing and physical disk I/O.
The sizes of these SGA components can be managed in two ways: manually and automatically.
If you choose to manage these components manually, you must specify the size of each
SGA component and then increase or decrease the size of each component according to the
needs of the application. If these components are managed automatically, the instance itself will
monitor the utilization of each SGA component and adjust their sizes accordingly, relative to a
predefined maximum allowable aggregate SGA size.