前面已经对Oracle的基本参数做了介绍,接下来会不定期写其他的参数
Undo_Retention
自动undo段管理
以下针对自动undo段管理(手动不做说明)
Retention Guarantee
如果开启Retention Guarantee的话,oracle会保证未过期的数据不会被覆盖,但是如果这样的话可能会引起DML操作失败
查询当前undo retention大小
select to_char(begin_time, 'DD-MON-RR HH24:MI') begin_time,
to_char(end_time, 'DD-MON-RR HH24:MI') end_time,
tuned_undoretention
from v$undostat
order by end_time;
查询当前undo 空间的使用率
SELECT round(((SELECT (NVL(SUM(bytes), 0))FROM dba_undo_extents
WHERE tablespace_name =
(select value from v$parameter
where lower(name) = 'undo_tablespace')
AND status IN ('ACTIVE', 'UNEXPIRED')) * 100) /
(SELECT SUM(bytes) FROM dba_data_files
WHERE tablespace_name =
(select value from v$parameter
where lower(name) = 'undo_tablespace')), 2) PCT_INUSE
FROM dual
实际环境截图
参考连接
https://docs.oracle.com/cd/B28359_01/server.111/b28320/initparams251.htm#REFRN10225