-- lets create some junk table and throw some data and check the size of table
-- when there are no records, the size is just initally allocated 
-- after throwing records, it will grow.
-- when deleted, space is not released. When truncated space is released.

mag@mutation_mutation > create table myTable (id number, name char(30))
  2  ;

Table created.

mag@mutation_mutation > truncate table mytable;

Table truncated.

mag@mutation_mutation > @/tmp/checksize

size_in_megs
------------
       .0625
mag@mutation_mutation > @/tmp/insert

PL/SQL procedure successfully completed.

mag@mutation_mutation > @/tmp/checksize

size_in_megs
------------
        .125

mag@mutation_mutation > @/tmp/insert

PL/SQL procedure successfully completed.

mag@mutation_mutation > @/tmp/checksize

size_in_megs
------------
       .1875

mag@mutation_mutation > delete from mytable;

2666 rows deleted.

mag@mutation_mutation > commit;

Commit complete.

mag@mutation_mutation > @/tmp/checksize

size_in_megs
------------
       .1875

mag@mutation_mutation > truncate table mytable;

Table truncated.

mag@mutation_mutation > @/tmp/checksize

size_in_megs
------------
       .0625

mag@mutation_mutation > get /tmp/insert
  1     begin
  2     for mag in ( select rownum,segment_name from dba_segments) loop
  3     insert into mytable values (mag.rownum,mag.segment_name);
  4     end loop;
  5     commit;
  6* end;
mag@mutation_mutation > get /tmp/checksize
  1*  select bytes / (1024*1024) as "size_in_megs" from user_segments where segment_name = 'MYTABLE'
mag@mutation_mutation >