reclaim disk space from oracle tablespace;

select 'alter database datafile ' || a.file_id || ' resize ' || round((a.bytes - b.free_space + 1024*1024)/1024/1024)|| 'm ;'
from dba_data_files a,
(select sum(bytes) free_space , file_id from dba_free_space group by file_id) b
where a.file_id = b.file_id
;

----------
----------

set verify off
column file_name format a50 word_wrapped
column smallest format 999,990 heading "Smallest|Size|Poss."
column currsize format 999,990 heading "Current|Size"
column savings format 999,990 heading "Poss.|Savings"
break on report
compute sum of savings on report

column value new_val blksize
select value from v$parameter where name = 'db_block_size'
/

select file_name,
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 ) smallest,
ceil( blocks*&&blksize/1024/1024) currsize,
ceil( blocks*&&blksize/1024/1024) -
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 ) savings
from dba_data_files a,
( select file_id, max(block_id+blocks-1) hwm
from dba_extents
group by file_id ) b
where a.file_id = b.file_id(+)
/

column cmd format a75 word_wrapped

select 'alter database datafile '''||file_name||''' resize ' ||
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 ) || 'm;' cmd
from dba_data_files a,
( select file_id, max(block_id+blocks-1) hwm
from dba_extents
group by file_id ) b
where a.file_id = b.file_id(+)
and ceil( blocks*&&blksize/1024/1024) -
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 ) > 0
/


references:
http://dbaforums.org/oracle/index.php?showtopic=4444
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:54178027703899
http://asktom.oracle.com/pls/asktom/f?p=100:11:3259860865329305::::P11_QUESTION_ID:153612348067