Difference for BYTES between dba_segments and dba_extents

Hi everybody,

I know there are some more questions depending my headline here in the community portal, but the difference of my data is, i think, very special and I've already tries the points regarding from these docs without a solution for the difference:

• Doc ID 463101.1
• Doc ID 352330.1

For monitoring purposes I want to monitor the usage of datafiles. For that I've this statement:

select

ROWNUM AS ID,

SYSDATE AS COLLECTOR_TIMESTAMP,

df.file_name AS DATAFILE_NAME,

  df.tablespace_name as TABLESPACE_NAME,

  decode(df.MAXBYTES/1024/1024/1024,0,df.bytes/1024/1024/1024,df.MAXBYTES/1024/1024/1024) as MAXSIZE_IN_GB,

  (df.bytes/1024/1024/1024) as ACTUAL_SIZE_IN_GB,