参考官方说明

IMMEDIATE or DEFERRED

Indicates whether or not the buffer pool will be created immediately.

IMMEDIATE

The buffer pool will be created immediately. If there is not enough reserved space in the database shared memory to allocate the new buffer pool (SQLSTATE 01657) the statement is executed as DEFERRED.

DEFERRED

The buffer pool will be created when the database is deactivated (all applications need to be disconnected from the database). Reserved memory space is not needed; required memory will be allocated from the system.