Oracle Architecture - Oracle Essentials - page 57

Prior to Oracle9 i , the size of the SGA was set when the Oracle instance was started. The
only way to change the size of the SGA or any of its components was to change the
initialization parameter and then stop and restart the instance. Since Oracle9 i , you can
also change the size of the SGA or its components while the Oracle instance is running.
Oracle9 i also introduced the concept of the granule , which is the smallest amount of
memory that you can add to or subtract from the SGA.
Oracle Database 10 g introduced Automatic Shared Memory Management, while Oracle
Database 11 g added Automatic Memory Management for the SGA and PGA instance
components. Whenever the MEMORY_TARGET (new to Oracle Database 11 g ) or
SGA_TARGET initialization parameter is set, the database automatically distributes the
memory among various SGA components providing optimal memory management.
The shared memory components automatically sized include the shared pool (manually
set using SHARED_POOL_SIZE), the large pool (LARGE_POOL_SIZE), the Java pool
(JAVA_POOL_SIZE), the buffer cache (DB_CACHE_SIZE), and the streams pool
(STREAMS_POOL_SIZE). Automatic memory management initialization parameters
can be set through Oracle Enterprise Manager.
The background processes interact with the operating system and each other to manage
the memory structures for the instance. These processes also manage the actual database
on disk and perform general housekeeping for the instance.
Figure 2-8 illustrates the memory structures and background processes discussed in the
following section.
Figure 2-8. An Oracle instance