select * from dba_rollback_segs...不阻塞session

Column	Datatype	NULL	Description
`SEGMENT_NAME`	`VARCHAR2(30)`	`NOT NULL`	Name of the rollback segment
`OWNER`	`VARCHAR2(6)`		Owner of the rollback segment
`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`	File identifier number of the file containing the segment head
`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
`INSTANCE_NUM`	`VARCHAR2(40)`		Rollback segment owning Real Application Clusters instance number
`RELATIVE_FNO`	`NUMBER`	`NOT NULL`	Relative file number of the segment header

segment header 其中id多是记录彼此相连接的头信息地址 datafile_header等

[@more@]

1、oracle能够实现undo暂存机制，通过生成trc文件可以解析该过程；

2、

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rollback segment不阻塞session