说明：生产环境中，很多时候需要查询数据库SGA和PGA实际占用大小以了解内存使用情况.
以下为测试结果：
SELECT ROUND((a.SGA_MEM + b.PGA_MEM), 2) "TOTAL_MEMORY",
       ROUND(a.SGA_MEM, 2) sga,
       ROUND(b.PGA_MEM, 2) pga
  FROM (SELECT SUM(current_size) / 1024 / 1024 "SGA_MEM"
          FROM v$sga_dynamic_components,
               (SELECT SUM(pga_alloc_mem) / 1024 / 1024 "PGA_MEM"
                  FROM v$process) a
         WHERE component IN ('shared pool',
                             'large pool',
                             'java pool',
                             'streams pool',
                             'DEFAULT buffer cache')) a,
       (SELECT SUM(pga_alloc_mem) / 1024 / 1024 "PGA_MEM" FROM v$process) b;

TOTAL_MEMORY        SGA        PGA
------------ ---------- ----------
      2991.3       2848      143.3