Dba_extents describes the extents comprising the segments in all tablespaces in the database. Note that if a datafile (or entire tablespace) are offline in a locally managed tablespace, you'll not see any extent inf Ormation. If an object have extents in a online file of the tablespace, you'll see extent information about the offline datafile. However, if the object is entirely in the offline file, a query of this view won't return any records. Related View User_extents describes the extents comprising the segments owned by the current USER ' s objects. This view does not display the OWNER, file_id, block_id, or relative_fno columns. This means that Dba_extends describes the extended information in the middle of all the table spaces in the database. You must use Dba_extends to ensure that the corresponding data file is in the online state, otherwise you cannot return any records. For one, the user_extents view is often used, with fewer fields than the Dba_extends view.
----------------------------------------------------------------------------------------------------------- ---------------------Dba_segments describes the storage allocated for all segments in the database. Related View user_segments describes the storage allocated for the segments owned by the current USER ' s objects. This view does not display the OWNER, Header_file, Header_block, or relative_fno columns. The dba_segments view describes the storage and allocation information for all segments in the database. The segment contains multiple extents, which are the lowest-level view visible to the data-related user, and through these two views, we can know the tablespace, data file number, and partition where a record resides. You can also know the size of each storage segment and the expansion area information. Reprint Please specify source: http://www.cnblogs.com/pengineer/p/4385312.html
Oracle dba_extents views and dba_segments views
