Oracle教程 2023-02-25

Oracle 视图 DBA_ROLLBACK_SEGS 官方解释，作用，如何使用详细说明

Oracle视图DBA_ROLLBACK_SEGS用来显示可回滚段（Rollback Segments）的定义。

DBA_ROLLBACK_SEGS视图只适用于Oracle 7.3及以上版本，每条DBA_ROLLBACK_SEGS视图记录表示一个定义有效的回滚段（rollback segment）。

使用DBA_ROLLBACK_SEGS视图：
1.查看当前数据库中所有回滚段的详细信息：
SELECT * FROM dba_rollback_segs;

2.查询出某一具体回滚段的状态：
SELECT STATUS, SEGMENT_ID FROM dba_rollback_segs WHERE SEGMENT_NAME= ‘ROLLBACK_TEST’;

3.查看回滚段的创建细节：
SELECT * FROM dba_rollback_segs WHERE SEGMENT_NAME= ‘ROLLBACK_TEST’;

DBA_ROLLBACK_SEGS describes rollback segments.

Column	Datatype	NULL	Description
`SEGMENT_NAME`	`VARCHAR2(30)`	`NOT NULL`	Name of the rollback segment
`OWNER`	`VARCHAR2(6)`		Owner of the rollback segment: `PUBLIC` `SYS`
`TABLESPACE_NAME`	`VARCHAR2(30)`	`NOT NULL`	Name of the tablespace containing the rollback segment
`SEGMENT_ID`	`NUMBER`	`NOT NULL`	ID number of the rollback segment
`FILE_ID`	`NUMBER`	`NOT NULL`	Absolute file number of the data file containing the segment header
`BLOCK_ID`	`NUMBER`	`NOT NULL`	ID number of the block containing the segment header
`INITIAL_EXTENT`	`NUMBER`		Initial extent size in bytes
`NEXT_EXTENT`	`NUMBER`		Secondary extent size in bytes
`MIN_EXTENTS`	`NUMBER`	`NOT NULL`	Minimum number of extents
`MAX_EXTENTS`	`NUMBER`	`NOT NULL`	Maximum number of extent
`PCT_INCREASE`	`NUMBER`		Percent increase for extent size
`STATUS`	`VARCHAR2(16)`		Rollback segment status: `OFFLINE` `ONLINE` `NEEDS RECOVERY` `PARTLY AVAILABLE` `UNDEFINED`
`INSTANCE_NUM`	`VARCHAR2(40)`		Rollback segment owning Oracle Real Application Clusters instance number
`RELATIVE_FNO`	`NUMBER`	`NOT NULL`	Relative file number of the segment header

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