sga_max_size discrepancy

From: Keith Moore <kmoore_at_zephyrus.com>
Date: Wed, 30 Jul 2008 17:15:52 -0500 (CDT)
Message-ID: <28610.206.227.160.10.1217456152.squirrel@lady.zephyrus.com>

Oracle EE 10.2.0.3
Solaris 10, running in a zone

These are development databases so SGA is very small. I am not setting sga_max_size or sga_target. I set the sga sizes as follows:

db_cache_size=128M
shared_pool_size=100M
log_buffer=10485760
java_pool_size=0

According to the Reference manual, if sga_max_size is not set is should be the sum of the individual components (buffer pool, shared pool, etc).

That is now what happens. The buffer cache is increased to 256M and sga_max_size is set to 372M.

SQL> show sga

Total System Global Area 390070272 bytes

Fixed Size                  2030264 bytes
Variable Size             104858952 bytes
Database Buffers          268435456 bytes
Redo Buffers               14745600 bytes

SQL> show parameter sga_max_size

NAME                                 TYPE        VALUE


------------------------------------ ----------- ------------------------------

sga_max_size                         big integer 372M

SQL> show parameter db_cache_size

NAME                                 TYPE        VALUE


------------------------------------ ----------- ------------------------------

db_cache_size                        big integer 256M

SQL> show parameter shared_pool_size

NAME                                 TYPE        VALUE


------------------------------------ ----------- ------------------------------

shared_pool_size                     big integer 100M

I can set sga_max_size and that should solve it but I'm wondering why this is working this way.

Keith

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Received on Wed Jul 30 2008 - 17:15:52 CDT