difference sga

may i know the difference between sga_max_size and sga_target
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johanntagleConnect With a Mentor Commented:

Can't explain it better than that.
sga_max_size is the maximum amount of memory the SGA can consume. It will be allocated in shared memory. It is OS dependant, and also dependant on other settings. Oracle will try to pre-allocate all of that memory on startup, which will be virtual so may not physically allocate them until needed, but depending on OS and other Oracle (pre_page_sga and lock_sga) settings, Oracle may also try to pin the memory (causing a hard allocation) at startup. You monitor it somewhat on UNIX platforms with the "ipcs" command.

sga_target is for automatic memory management, telling Oracle how much ideal memory it needs. The sga_target can be much less than the sga_max_size, however it can grow up to sga_max_size.
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