By default,
Oracle 11g is configured for Automatic Memory Management. If you configure
Automatic Shared MemoryManagement and make no other changes, you will
implicitly enable Automatic PGA Memory Management. Setting SGA_TARGET to a
nonzero value doesn‘t immediately enable Automatic Shared Memory Management
because you may still have Automatic Memory Management enabled. Setting the
parameter SGA_MAX_SIZE to nonzero puts a cap on manual SGA configuration, but
again it does not implement Manual Shared Memory Management. The value of
PGA_AGGREGATE_TARGET is relevant only if Automatic Memory Management is not
configured, so you must also set MEMORY_TARGET to zero for it to take effect.