SGA size at Oracle 10G startup

The SGA size for Oracle 10g library startup is determined by Sga_target and Sga_max_size and is discussed in the following three scenarios

Sga_target=sga_max_size

Parameter file specified value

*.sga_target=599785472

Start

SQL> startupORACLE instance started.Global Area  599785472bytesFixed Size          2022632bytesVariable Size         171967256bytesDatabase Buffers      423624704bytesRedo Buffers            2170880bytesDatabase mounted.Database opened.

Sga_target < Sga_max_size
Parameter file specified value

*.sga_max_size=800m*.sga_target=700m

Start the database

sql>  startuporacle Instance Started Total System global  area 838860800  bytes  Fixed Size 2024496  bytes< /span>variable  Size 297798608  bytes  Database buffers 536870912   Bytes  Redo buffers 2166784  bytes  datab ASE Mounted Database opened  

SQL> select 838860800/1024/1024 from dual;838860800/1024/1024-------------------        800SQL> show parameter sga_NAME                   TYPE      VALUE------------------- ----------- -----------------------sga_max_size         big integer 800Msga_target           big integer 700M

Sga_target>sga_max_size

Parameter file specified value

*.sga_max_size=600m*.sga_target=700m

And the size of the database actually started

sql>  startuporacle Instance Started Total System global  area 734003200  bytes  Fixed Size 2023656  bytes< /span>variable  Size 192941848  bytes  Database buffers 536870912   Bytes  Redo buffers 2166784  bytes  datab ASE Mounted Database opened  

SQL> select 734003200/1024/1024 from dual;734003200/1024/1024-------------------        700SQL> show parameter sga_   NAME                     TYPE    VALUE------------------------------------ ----------- ------------------------------sga_max_size                 big integer 700Msga_target               big integer 700M

Experimental Conclusion
As can be seen from the above three experiments, the size of the SGA at database startup is determined by the larger values in Sga_target and sga_max_size

When Sga_target <= sga_max_size, the sga_max_size shall prevail.
When Sga_target > Sga_max_size, the value of Sga_target is given to sga_max_size and then to Sga_max_size

SGA size at Oracle 10G startup