adding datafile to a LOCAL managed TS - 64k overhead

                 Adding datafile to a LOCAL managed TS - 64k overhead

PROBLEM:
----------
After adding 327680K datafile to a tablespace the free space of that datafile 
shows as 163840K although there are no EXTENTS have been allocated/reported in 
the DBA_EXTENTS view.


                                                       *** DATAFILE USAGE ***
                                                                                                         %
Tablespace Name File Name                                   Size KB    Free KB   Size MB   Free MB    Used
--------------- ---------------------------------------- ---------- ---------- --------- --------- -------
XDW_LRGD01      /u06/oradata/XYLADW/xdw_lrgd01_03.dbf       1966144     163840  1,920.06    160.00   91.67
XDW_LRGD01      /u06/oradata/XYLADW/xdw_lrgd01_04.dbf        327680     163840    320.00    160.00   50.00
XDW_LRGD01      /u06/oradata/XYLADW/xdw_lrgd01_01.dbf       1966144          0  1,920.06       .00  100.00
XDW_LRGD01      /u06/oradata/XYLADW/xdw_lrgd01_02.dbf       1966144          0  1,920.06       .00  100.00


12:26:24 SYSTEM@XYLADW:olympia> select RELATIVE_FNO
12:26:37   2  from dba_data_files
12:26:41   3  where file_name='/u06/oradata/XYLADW/xdw_lrgd01_04.dbf';

RELATIVE_FNO
------------
          11

1 row selected.

12:27:02 SYSTEM@XYLADW:olympia> select bytes/1024 kbytes
12:27:27   2  from dba_data_Files
12:27:33   3  where RELATIVE_FNO=11;

    KBYTES
----------
    327680

1 row selected.

12:27:36 SYSTEM@XYLADW:olympia> ttit off
12:27:44 SYSTEM@XYLADW:olympia> select bytes/1024 free_kbytes
12:27:56   2  from dba_free_Space
12:28:00   3  where RELATIVE_FNO=11;

FREE_KBYTES
-----------
     163840

1 row selected.

12:28:04 SYSTEM@XYLADW:olympia> select segment_name
12:28:14   2  from dba_extents
12:28:18   3  where RELATIVE_FNO=11;

no rows selected

12:28:22 SYSTEM@XYLADW:olympia>

12:29:06 SYSTEM@XYLADW:olympia> select file_name, tablespace_name
12:29:20   2  from dba_data_Files
12:29:22   3  where RELATIVE_FNO=11;

Data File Name                           Tablespace Name
---------------------------------------- ---------------
/u06/oradata/XYLADW/xdw_lrgd01_04.dbf    XDW_LRGD01

1 row selected.

12:29:28 SYSTEM@XYLADW:olympia> select * from dba_tablespaces
12:29:35   2  where tablespace_name='XDW_LRGD01';

Tablespace Name INITIAL_EXTENT NEXT_EXTENT MIN_EXTENTS MAX_EXTENTS PCT_INCREASE MIN_EXTLEN STATUS    CONTENTS  LOGGING   EXTENT_MAN ALLOCATIO PLU
--------------- -------------- ----------- ----------- ----------- ------------ ---------- --------- --------- --------- ---------- --------- ---
XDW_LRGD01           167772160   167772160           1  2147483645            0  167772160 ONLINE    PERMANENT LOGGING   LOCAL      UNIFORM   NO

1 row selected.

12:29:44 SYSTEM@XYLADW:olympia>


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SOLUTION:
----------
You must add 64K for the DBF header in a LOCAL managed TS the extent map is 
stored in the 64K header of the datafile apparently if you don't accommodate for 
that overhead ORACLE will use the UNIFORM extent size to store it's bitmap of 
the extents and since this TS has 160MB UNIFORM extents it's a HUGE waste of 
space.


-- adding 64K for the dbf header
--  [327680+64=327744]
12:29:44 SYSTEM@XYLADW:olympia> alter database datafile '/u06/oradata/XYLADW/xdw_lrgd01_04.dbf'
12:32:01   2  resize 327744k;

Database altered.

12:32:19 SYSTEM@XYLADW:olympia> select bytes/1024 free_kbytes
12:33:23   2  from dba_free_Space
12:33:28   3  where RELATIVE_FNO=11;

FREE_KBYTES
-----------
     327680

1 row selected.

.