Search notes:

Oracle System Global Area (SGA)

The SGA is the (shared) memory that an Oracle instance needs to operate. It consists of
A notable distinction between the Shared Pool and the buffer cache is that the shared pool primarily caches metadata while the buffer cache stores data.

SGA Granules

In 9i, the SGA architecture was reengineered with a concepts called granules. These allow to relocate memory between areas such as buffer cache and shared pool.
The size of the granules are dependent on OS, Oracle version and size of the SGA (MOS ID #947152.1).

Queries

select
   component,
   current_size/power(1024,2) size_mb,
   last_oper_type,
   last_oper_time,
   granule_size
from
   v$memory_dynamic_components
order by
   component;

See also

v$sga can be queried for the actual memory consumption of the SGA.
v$sga_dynamic_components, v$sga_dynamic_free_memory
memory management
oradebug dumpvar sga …
In order to run APEX, the SGA must be at least 300 MB.
init parameters:
x$ksmmem allows to read the value of every byte in the SGA.
The names of of SGA variables are listed in x$ksmfsv. 
oradebug dump global_area 2

Links

Kyle Hailey has written a C program to directly access the SGA.

Index