What are Fixed Size and Variable Size in SGA?

                            

SQL> show sga

Total System Global Area  431038464 bytes

Fixed Size                  1333676 bytes

Variable Size             306185812 bytes

Database Buffers          117440512 bytes

Redo Buffers                6078464 bytes

In the above result Database Buffers is belongs to component “db_block_size”

and Redo Buffers to “log buffer” but what about  Fixed Size  and  Variable Size                                          

Let’s find out them:

The fixed SGA is a component of the SGA that varies in size from platform to platform and release to release.The fixed SGA contains a set of variables that point to the other components of the SGA and variables that contain the values of various parameters.The size of the fixed SGA is something over which we have no control and it is generally very small.Think of this area as a bootstrap section of the SGA, something Oracle uses internally to find the other bits and pieces of the SGA.

The variable SGA is the sum of the "named" pools -- large pool, java pool and shared pool.

The variable size is MOST affected by java_pool_size + large_pool_size + shared_pool_size but other parameters will contribute to it (eg: every

control_file will consume 256 bytes of variable size memory.  If you have 4 controlfiles, the SGA will have 1024 bytes set aside for them) in a small way.

:-) 

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