Oracle 参数 UNDO_TABLESPACE 官方解释，作用，如何配置最优化建议
本站中文解释
undo_tablespace参数指定undo表空间，当数据库操作需要发生变更时，undo表空间会临时记录这些变更，提供高可用和回滚等功能。
正确设置方法：
1. 首先确保undo表空间处于自动模式，即设置参数 undo_management=auto。
2. 设置undo_tablespace参数，它指定undo表空间的名称。推荐在该参数指定undo表空间时采用对象名，即undo_tablespace=undo_ts。
3. 确保undo表空间处于可用状态，可以通过select status from dba_tablespaces where tablespace_name=’UNDO_TS’；查询。
4. 如果undo表空间不可用，可以执行alter tablespace undo_ts read write; 把undo表空间改为可用状态。
5. 把当前正在使用的实例修改成正常状态，可以执行shutdown immediate; startup; 或alter system set undo_tablespace=undo_ts scope=both; 语句。
6. 重新启动数据库实例，undo表空间就被正确设置了。
官方英文解释
UNDO_TABLESPACE specifies the undo tablespace to be used when an instance starts. If this parameter is specified when the instance is in manual undo management mode, then an error will occur and startup will fail.
| Property | Description |
|---|---|
|
Parameter type |
String |
|
Syntax |
|
|
Default value |
The first available undo tablespace in the database. |
|
Modifiable |
|
|
Modifiable in a PDB |
Yes |
|
Range of values |
Legal name of an existing undo tablespace |
|
Basic |
Yes |
|
Oracle RAC |
Each instance must have a unique value for this parameter, when it is set. |
If the UNDO_TABLESPACE parameter is omitted, the first available undo tablespace in the database is chosen. If no undo tablespace is available, the instance will start without an undo tablespace. In such cases, user transactions will be executed using the SYSTEM rollback segment. You should avoid running in this mode under normal circumstances.
You can replace an undo tablespace with another undo tablespace while the instance is running.
Note:
When you update this parameter on the primary database in an Oracle Data Guard configuration, you must also update it on all the physical standby databases in the configuration. This ensures that the standby databases can find the undo tablespace when they become the primary database.
See Also:
Oracle Database SQL
Language Reference for information about creating undo tablespaces
