create table T1
(
  ID   NUMBER,
  NAME VARCHAR2(10)
)
tablespace USERS

blocks       bytes                     extent
   8              65536                   1          

////////////////////////////////////////////////////////
DECLARE
                 x number :=0;
                BEGIN
                               for i in 1..50000 LOOP
                                        insert into t1 values  (i,i+1);
                                        x :=x  +1;  

                                        if x > 50 then

                                        commit;
                                        x :=0;
                              end if; 
                   End Loop; 
                   commit; 
                   END;
////////////////////////////////////////////////////////////    50000  是个变的值  80000 时候做比较
select owner,segment_name,segment_type,header_file,bytes,blocks,extents from dba_segments where segment_name='T1';          (50000)

         owner      segment_name        segment_type    header_file              bytes                blocks           extents     
 
         scott         T1                                table                       4                            983040              120                 15             120=15*8

select     *     from   dba_extents     where segment_name='T1'      查看各个extent 信息 

select owner,segment_name,segment_type,header_file,bytes,blocks,extents from dba_segments where segment_name='T1';         (80000)

         owner      segment_name        segment_type    header_file              bytes                blocks           extents      

         scott         T1                                table                       4                           2097152                256              17             256<>17*8


select owner,segment_name,segment_type, extent_id, file_id,block_id, bytes,blocks    from dba_extents where segment_name='T1'    查看各个extent 信息 

1                                          segment_name                        extentd_id                                                     bytes                      blocks
.......
14                         SCOTT                 T1             TABLE                   13          4            2145                        65536                   8
15                        SCOTT                  T1             TABLE                    14         4            2153                         65536                   8
16                        SCOTT                  T1             TABLE                    15         4             2161                        65536                   8
17                        SCOTT                  T1             TABLE                    16         4             3209                        1048576              128              (说明第17个extent 128个block大)