1. db_block_size,db_block_buffers,db_cache_size
    db_block_size:oracle read/write unit,Do not alter it afterward,standard block.
    db_block_buffers:before 9i, db_buffer_chche=db_block_buffers*db_block_size, DB_BLOCK_BUFFERS to control the size of the buffer cache
    db_cache_size:specifies the size of the DEFAULT buffer pool for buffers with the primary block size .
    db_nk_cache_size::specifies the size of the buffer pool for non standard block.
2. sga_max_size : the maxsize of sga
                           specify the maxsize mem of os acllocate the oracle database.
                           static
    sga_target: the maxsize of sga.
                      enable Automatic Shared Memory Management(asmm),
                      sga_taget=0 disable asmm.
                      sga_taget<=sga_max_size.
                      dynamic