Which statement describes the information returned by the DBMS_SPACE.SPACE_USAGE procedure for LOB space usage?
A. It returns space usage of only BasicFile LOB chunks.
B. It returns space usage of only SecureFile LOB chunks.
C. It returns both BasicFile and SecureFile LOB space usage for only nonpartitioned tables.
D. It returns both BasicFile and SecureFile LOB space usage for both partitioned and nonpartitioned tables.
开始是认为答案是D，依据官方文档的意思和题目选项含义应该是返回的 space usage of only SecureFile LOB是准确的，非space usage of only SecureFile LOB chunks是在高水位线以下的，并非实际的space usage。
高水位线 https://www.cnblogs.com/linjiqin/archive/2012/01/15/2323030.html
The first form of the procedure shows the space usage of data blocks under the segment High Water Mark. You can calculate usage for LOBs, LOBPARTITIONS and LOB SUBPARTITIONS. This procedure can only be used on tablespaces that are created with auto segment space management. The bitmap blocks, segment header, and extent map blocks are not accounted for by this procedure. Note that this overload cannot be used on SECUREFILE LOBs.
The second form of the procedure returns information about SECUREFILE LOB space usage. It will return the amount of space in blocks being used by all theSECUREFILE LOBs in the LOB segment. The procedure displays the space actively used by the LOB column, freed space that has retention expired, and freed space that has retention unexpired. Note that this overload can be used only on SECUREFILE LOBs.