Oracle DBA_EXTENTS view and DBA_SEGMENTS View

Oracle DBA_EXTENTS view and DBA_SEGMENTS View
DBA_EXTENTS describes the extents comprising the segments in all tablespaces in the database. note that if a datafile (or entire tablespace) is offline in a locally managed tablespace, you will not see any extent information. if an object has extents in an online file of the tablespace, you will see extent information about the offline datafile. however, if the object is entirely in the offline fil E, a query of this view will not 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. that is to say, DBA_EXTENDS describes the extended information of all tablespace segments in the database. When using DBA_EXTENDS, you must ensure that the corresponding data file is in the online State; otherwise, no records can be returned. For the USER_EXTENTS view, which is usually used, there are several fewer fields than the DBA_EXTENDS view.Slave --------------------------------------------------------------------------------------------------------------------------------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 of all segments in the database. The segment contains multiple expansion zones. The expansion zone is the bottom-layer view visible to data-related users. Through these two views, we can know the tablespace where a record is located, data File number and partition. You can also know the size and extended area information of each storage segment.