useful when resizing datafile

this script i got from asktom.com is a usefull script to determine what object/s are in the end of the datafile which will cause for you to not to shrink it the way you want it to shrink :) (I mean if there is a big free space between that object and the other object)

column tablespace_name format a20
column "Name" format a45
break on file_id skip 1
ttitle &1
select file_id, block_id, blocks,
owner||'.'||segment_name "Name"
from sys.dba_extents
where tablespace_name = upper('&1')
UNION
select file_id, block_id, blocks,
'Free'
from sys.dba_free_space
where tablespace_name = upper('&1')
order by 1,2,3
/

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"
set pages 3000
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
/