Oracle Database Discussions

Hello guys,
i am a little bit confused about setting sga_target and sizing log_buffer manually.

At first the documentation:
http://download-uk.oracle.com/docs/cd/B19306_01/server.102/b14237/initparams192.htm#sthref792

The following pools are manually sized components and are not affected by Automatic Shared Memory Management:
* Log buffer
* Other buffer caches, such as KEEP, RECYCLE, and other block sizes
* Fixed SGA and other internal allocations


Ok.. now my Oracle 10gR2 database:
- spfile:
-----------------------------------------------------------------
*.log_buffer=1048576
*.sga_target=3154116608
-----------------------------------------------------------------

Ok now in my opinion, the log_buffer should not be changed by oracle AMM.
So lets have a look:

SQL> show parameter log_buffer
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_buffer integer 14254080


SQL> show sga
Total System Global Area 3154116608 bytes
Fixed Size 2074600 bytes
Variable Size 603981848 bytes
Database Buffers 2533359616 bytes
Redo Buffers 14700544 bytes

Oh ok.... why does oracle change my manually sized value log_buffer from 1MB up to 14MB!!! (have a look at the output of show sga!)

Hmm and now?
What is right and what is wrong?

Maybe someone can clear the confusion...

Thanks and Regards
Stefan