Used part of the tablespace

Question

Hi
I appreciate if anyone can clear my doubts.
create tablespace test datafile
'C:\test.dbf' size 50M
extent management local uniform size 10M
When I check the used space of this tablespace:
I notice that
1-)Even the tablespace is empty, it shows 10M as a used part ?
2-)When I create an empty table in this tablespace, the used part becomes 20M ? Since the table is empty why used part increase? It should increase after the rows inserted into the table? I know 10M of extent allocated for the table, but it should be free for inserts, why does it occupy space in used part?
Thanks

Answer 1

so the below script doesnt show the free blocks inside the extents of segments.
Even it shows there is not available space in the tablespace, there might be space available inside the extents of the segments....
Am I right??
select (select decode(extent_management,'LOCAL','*',' ')
          from dba_tablespaces where tablespace_name = b.tablespace_name) ||
nvl(b.tablespace_name,
             nvl(a.tablespace_name,'UNKOWN')) name,
       kbytes_alloc kbytes,
       kbytes_alloc-nvl(kbytes_free,0) used,
       nvl(kbytes_free,0) free,
       ((kbytes_alloc-nvl(kbytes_free,0))/
                          kbytes_alloc)*100 pct_used,
       nvl(largest,0) largest,
       nvl(kbytes_max,kbytes_alloc) Max_Size,
       decode( kbytes_max, 0, 0, (kbytes_alloc/kbytes_max)*100) pct_max_used
from ( select sum(bytes)/1024 Kbytes_free,
              max(bytes)/1024 largest,
              tablespace_name
       from  sys.dba_free_space
       group by tablespace_name ) a,
     ( select sum(bytes)/1024 Kbytes_alloc,
              sum(maxbytes)/1024 Kbytes_max,
              tablespace_name
       from sys.dba_data_files
       group by tablespace_name
       union all
      select sum(bytes)/1024 Kbytes_alloc,
              sum(maxbytes)/1024 Kbytes_max,
              tablespace_name
       from sys.dba_temp_files
       group by tablespace_name )b
where a.tablespace_name (+) = b.tablespace_name
order by &1