> select name, bytes/1048576 mb, resizeable
from v$sgainfo t
where name in ('Granule Size', 'Redo Buffers', 'Maximum SGA Size', 'Fixed SGA Size')
model dimension by (name) measures(bytes, resizeable, 0 diff)
(bytes['fixed+log buffer']=bytes['Fixed SGA Size']+bytes['Redo Buffers'], 
 bytes['diff']=1048576*(
    ceil((bytes['Fixed SGA Size']+bytes['Redo Buffers'])/bytes['Granule Size'])*bytes['Granule Size']
        -(bytes['Fixed SGA Size']+bytes['Redo Buffers']))
);

NAME                              MB    RES
------------------------- ------.------ ---
Maximum SGA Size          393216        No 
Granule Size                 512        No 
Fixed SGA Size                25.127693 No 
Redo Buffers                 998.871094 No 
fixed+log buffer            1023.998787    
granule count                         2    
diff                               1272    

> select display_value, isdefault from v$parameter where name = 'log_buffer';

DISPLAY_VA ISDEFAULT 
---------- ----------
512M       FALSE