通过查看监控orabbix，看到一个sql语句，可以查看oracle数据库真实大小。
SELECT
to_char(
sum(
NVL( a.bytes / 1024 / 1024 / 10 - NVL( f.bytes / 1024 / 1024 / 10, 0 ), 0 )
),
'FM99999999999999990'
) retvalue
FROM
sys.dba_tablespaces d,
( SELECT tablespace_name, sum( bytes ) bytes FROM dba_data_files GROUP BY tablespace_name ) a,
( SELECT tablespace_name, sum( bytes ) bytes FROM dba_free_space GROUP BY tablespace_name ) f
WHERE
d.tablespace_name = a.tablespace_name ( + )
AND d.tablespace_name = f.tablespace_name ( + )
AND NOT ( d.extent_management LIKE 'LOCAL' AND d.contents LIKE 'TEMPORARY' )
