DBA_UNDO_EXTENTS

DBA_UNDO_EXTENTS描述了undo的所有段信息

The status of the undo space distribution reported by DBA_UNDO_EXTENTS is correct for the undo tablespace that is active on the instance on which DBA_UNDO_EXTENTS is queried.However, due to the use of in-memory information that is different on each instance, there can be a discrepancy in the status of the undo spacedistribution of undo tablespaces active on other instances when queried fromone instance. This does not affect undo functionality and is only a reportingdiscrepancy for other instances' undo tablespace space distribution status. Asa best practice, query the space distribution for an undo tablespace from theinstance on which it is active.

Column              Datatype        NULL       DescriptionOWNER               CHAR(3)                    Owner of the undo tablespaceSEGMENT_NAME        VARCHAR2(30)    NOT NULL   Name of the undo segmentTABLESPACE_NAME     VARCHAR2(30)    NOT NULL   Name of the undo tablespaceEXTENT_ID           NUMBER                     ID of the extentFILE_ID             NUMBER          NOT NULL   File identifier number of the file containing the extentBLOCK_ID            NUMBER                     Start block number of the extentBYTES               NUMBER                     Size of the extent (in bytes)BLOCKS              NUMBER                     Size of the extent (in blocks)RELATIVE_FNO        NUMBER                     Relative number of the file containing the segment headerCOMMIT_JTIME        NUMBER                     Commit time of the undo in the extent expressed as Julian time. This                                                   column is deprecated, but retained for backward compatibility reasons.COMMIT_WTIME        VARCHAR2(20)               Commit time of the undo in the extent expressed as Wallclock time.Thi                                                  s column is deprecated, but retained for backward compatibility reasons.STATUS              VARCHAR2(9)                Transaction Status of the undo in the extent:                                                  ACTIVE                                                  EXPIRED                                                  UNEXPIRED