what is meant by the minimum SGA is three granules

The minimum SGA is three granules is:



1- One Granule for Fixed SGA (includes redo buffers)

2- One Granule for Buffer Cache

3- One Granule for Shared Pool











for More :

http://download.oracle.com/docs/cd/B19306_....102/b14231.pdf

Components and Granules in the SGA

The SGA comprises a number of memory components, which are pools of memory
used to satisfy a particular class of memory allocation requests. Examples of memory
components include the shared pool (used to allocate memory for SQL and PL/SQL
execution), the java pool (used for java objects and other java execution memory), and
the buffer cache (used for caching disk blocks). All SGA components allocate and
deallocate space in units of granules. Oracle Database tracks SGA memory use in
internal numbers of granules for each SGA component.

The memory for dynamic components in the SGA is allocated in the unit of granules.
Granule size is determined by total SGA size. Generally speaking, on most platforms,
if the total SGA size is equal to or less than 1 GB, then granule size is 4 MB. For SGAs
larger than 1 GB, granule size is 16 MB. Some platform dependencies may arise. For
example, on 32-bit Windows NT, the granule size is 8 MB for SGAs larger than 1 GB.
Consult your operating system specific documentation for more details.
You can query the V$SGAINFO view to see the granule size that is being used by an
instance. The same granule size is used for all dynamic components in the SGA.
If you specify a size for a component that is not a multiple of granule size, Oracle
Database rounds the specified size up to the nearest multiple. For example, if the
granule size is 4 MB and you specify DB_CACHE_SIZE as 10 MB, the database actually
allocates 12 MB.


Reference : Administrator's Guide 10g Release 2

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