一、oracle commonly table
1、dba_extents #describes the extents comprising the segments in all tablespaces in the database.

commonly column
owner
segment_name
partition_name
tablespace_name
blocks
bytes

2、dba_segments#describes the storage allocated for all segments in the database.

owner
segment_name
partition_name
segment_type *
segment_subtype # subtype of lob segment :sourcefile assm mssm and null
tablespace_name
bytes

NOTE：The next Blog describe the principles of  Oracle 12C RAC .