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Memory Parameter usage in Oracle 11gR2

MEMORY_TARGET specifies the Oracle system-wide usable memory.

MEMORY_TARGET specifies the Oracle system-wide usable memory.
MEMORY_MAX_TARGET (…) decide on a maximum amount of memory that you would want to allocate to the database for the foreseeable future.
The database tunes memory to the MEMORY_TARGET value, reducing or enlarging the SGA and PGA as needed.

In a text initialization parameter file, if you omit the line for MEMORY_MAX_TARGET and include a value for MEMORY_TARGET, the database automatically sets MEMORY_MAX_TARGET to the value of MEMORY_TARGET.

If you omit the line for MEMORY_TARGET and include a value for MEMORY_MAX_TARGET, the MEMORY_TARGET parameter defaults to zero.

Prior to Oracle 11g, the DBA used to set the sga_target and sga_max_size parameters, allowing Oracle to reallocate RAM within the SGA.  The PGA was independent, as governed by the pga_aggregate_target parameter.

Now in Oracle 11g we see the memory_max_target parameter which governs the total maximum RAM for both the PGA and SGA regions and the new memory_target parameter which governs the existing sizes.  This allows RAM to be de-allocated from the SGA and transferred to the PGA.

With this version, oracle has become smart as in exchanging memory between SGA and PGAs. This is a huge achievement.
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