How can free + used space tbs size, can someone explain

Question

Hi Gurus
Can someone explain this, How can free + used space in a tablespace can be greater than size of a tablespace. What am I missing here . Thanks a lot .
I am on 10.2.0.1, HP-UX
14:38:52 SQL> select owner,sum(bytes), sum(BYTES) /1024/1024 "MB" from dba_segments where tablespace
name='USERDB1ADATA' group by owner;
OWNER SUM(BYTES) MB
USERDB1A 839680000 800.78125
1 row selected.
14:40:42 SQL> select bytes, BYTES /1024/1024 "MB" from dba_data_files where tablespace_name='USERDB1
A_DATA';
BYTES MB
3758096384 3584
1 row selected.
14:40:42 SQL> select sum(bytes) , sum(BYTES) /1024/1024 "MB"from dba_free_space where tablespace_nam
e='USERDB1A_DATA';
SUM(BYTES) MB
3067412480 2925.3125
1 row selected.
14:40:43 SQL> select 839680000 + 3067412480 "used + free space" from dual;
used + free space
3907092480
1 row selected.
New DBA

Answer 1

Good point, Howard, about the recycle bin. So I cleaned up, recreated the table, filled it, dropped it but did not purge it, and ...
SQL> create table test.x tablespace test as select * from dba_objects where 1=2;
Table created.
SQL> insert into test.x select * from dba_objects;
12617 rows created.
SQL> commit;
Commit complete.
SQL> drop table test.x;
Table dropped.
SQL> with
  2  dbf_size as (select sum(bytes) size_
  3                 from dba_data_files where tablespace_name='TEST'),
  4  dbf_free as (select sum(bytes) free_
  5                 from dba_free_space where tablespace_name='TEST'),
  6  dbf_used as (select sum(bytes) used_
  7                 from dba_segments where tablespace_name='TEST')
  8  select size_, free_, used_, (size_ - free_ - used_) left_
  9         from dbf_size, dbf_free, dbf_used
10  /
     SIZE_      FREE_      USED_      LEFT_
   5242880    5177344    2162688   -2097152
SQL>and then I played around with my SQL and came up with
WITH
dbf_size AS (SELECT SUM(bytes) size_
               FROM dba_data_files
              WHERE tablespace_name='TEST'),
dbf_free AS (SELECT SUM(bytes) free_
               FROM dba_free_space
              WHERE tablespace_name='TEST'),
dbf_used AS (SELECT SUM(bytes) used_
               FROM dba_segments
              WHERE tablespace_name='TEST'),
dbf_fbin AS (SELECT SUM(bytes) fbin_
               FROM dba_segments
              INNER JOIN
                    dba_recyclebin
                 ON (tablespace_name=ts_name
                     AND segment_name=object_name)
              WHERE tablespace_name='TEST')
SELECT      size_, -- tablespace size
     free_, -- free space reported
     used_, -- segment space used
     fbin_, -- segment space in recycle bin
     (size_ - free_ - used_ + fbin_) left_ -- 64K overhead per data file
  FROM      dbf_size, dbf_free, dbf_used, dbf_fbin
/which does
SQL> WITH
  2  dbf_size AS (SELECT SUM(bytes) size_
  3                 FROM dba_data_files
  4                WHERE tablespace_name='TEST'),
  5  dbf_free AS (SELECT SUM(bytes) free_
  6                 FROM dba_free_space
  7                WHERE tablespace_name='TEST'),
  8  dbf_used AS (SELECT SUM(bytes) used_
  9                 FROM dba_segments
10                WHERE tablespace_name='TEST'),
11  dbf_fbin AS (SELECT SUM(bytes) fbin_
12                 FROM dba_segments
13                INNER JOIN
14                      dba_recyclebin
15                   ON (tablespace_name=ts_name
16                       AND segment_name=object_name)
17                WHERE tablespace_name='TEST')
18  SELECT     size_,
19     free_,
20     used_,
21     fbin_,
22     (size_ - free_ - used_ + fbin_) left_
23    FROM     dbf_size, dbf_free, dbf_used, dbf_fbin
24  /
     SIZE_      FREE_      USED_      FBIN_      LEFT_
   5242880    5177344    2162688    2162688      65536
SQL> alter tablespace test add datafile 'C:\ORACLE\ORADATA\XE\TEST2.DBF' size 5m;
Tablespace altered.
SQL> WITH
  2  dbf_size AS (SELECT SUM(bytes) size_
  3                 FROM dba_data_files
  4                WHERE tablespace_name='TEST'),
  5  dbf_free AS (SELECT SUM(bytes) free_
  6                 FROM dba_free_space
  7                WHERE tablespace_name='TEST'),
  8  dbf_used AS (SELECT SUM(bytes) used_
  9                 FROM dba_segments
10                WHERE tablespace_name='TEST'),
11  dbf_fbin AS (SELECT SUM(bytes) fbin_
12                 FROM dba_segments
13                INNER JOIN
14                      dba_recyclebin
15                   ON (tablespace_name=ts_name
16                       AND segment_name=object_name)
17                WHERE tablespace_name='TEST')
18  SELECT     size_, -- tablespace size
19     free_, -- free space reported
20     used_, -- segment space used
21     fbin_, -- segment space used in recycle bin
22     (size_ - free_ - used_ + fbin_) left_
23    FROM     dbf_size, dbf_free, dbf_used, dbf_fbin
24  /
     SIZE_      FREE_      USED_      FBIN_      LEFT_
  10485760   10354688    2162688    2162688     131072Message was edited by:
Hans Forbrich
Cleaned up the script and tested with second data file added to verify LMT overhead.