Am I understanding SGA_TARGET and SGA_MAX_SIZE correctly?

Question

Let's say I set SGA_MAX_SIZE to 1024MB and SGA_TARGET to 512MB.
As I understand it, this means that the total SGA size will never exceed 1024MB (that's the "hard cap"). Oracle will try to keep things around 512MB, but may burst up to 1024MB as needed.
Is that correct? Otherwise, I don't see the point of SGA_MAX_SIZE vs. SGA_TARGET.
BTW...I know MEMORY_TARGET and MEMORY_MAX_TARGET are the new 11g params, but Oracle ships XE with those turned off and the 10g SGA_* params and PGA_AGGREGATE_TARGET set...?

Answer 1

Hi,
In Oracle 11g MEMORY_TARGET is for automatic SGA and PGA management.MEMORY_MAX_SIZE is the maximum size to which your MEMORY_TARGET can be allocated.As shown below:
SQL> show parameter %MEMORY%
NAME TYPE VALUE
hi_shared_memory_address integer 0
memory_max_target big integer 1G
memory_target big integer 1G
But,When it comes to managing various other memory component like shared_pool,large_pool,Db_buffer_cache,log_buffer_cache,java_pool we still have to manage SGA_TARGET.
SQL> show parameter %SGA%
NAME TYPE VALUE
lock_sga boolean FALSE
pre_page_sga boolean FALSE
sga_max_size big integer 1G
sga_target big integer 0
Best regards,
Rafi.
http://rafioracledba.blogspot.com/
Edited by: Rafi (Oracle DBA) on Jun 22, 2011 11:54 PM