Oracle : Query to find how much space can be reclaimed from each datafile

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set linesize 1000 pagesize 0 feedback off trimspool on
hwm as (
— get highest block id from each datafiles ( from x$ktfbue as we don’t need all joins from dba_extents )
select /*+ materialize */ ktfbuesegtsn ts#,ktfbuefno relative_fno,max(ktfbuebno+ktfbueblks-1) hwm_blocks
from sys.x$ktfbue group by ktfbuefno,ktfbuesegtsn
hwmts as (
— join ts# with tablespace_name
select name tablespace_name,relative_fno,hwm_blocks
from hwm join v$tablespace using(ts#)
hwmdf as (
— join with datafiles, put 5M minimum for datafiles with no extents
select file_name,nvl(hwm_blocks*(bytes/blocks),5*1024*1024) hwm_bytes,bytes,autoextensible,maxbytes
from hwmts right join dba_data_files using(tablespace_name,relative_fno)
case when autoextensible=’YES’ and maxbytes>=bytes
then — we generate resize statements only if autoextensible can grow back to current size
‘/* reclaim ‘||to_char(ceil((bytes-hwm_bytes)/1024/1024),999999)
||’M from ‘||to_char(ceil(bytes/1024/1024),999999)||’M */ ‘
||’alter database datafile ”’||file_name||”’ resize ‘||ceil(hwm_bytes/1024/1024)||’M;’
else — generate only a comment when autoextensible is off
‘/* reclaim ‘||to_char(ceil((bytes-hwm_bytes)/1024/1024),999999)
||’M from ‘||to_char(ceil(bytes/1024/1024),999999)
||’M after setting autoextensible maxsize higher than current size for file ‘
|| file_name||’ */’
end SQL
from hwmdf
bytes-hwm_bytes>1024*1024 — resize only if at least 1MB can be reclaimed
order by bytes-hwm_bytes desc;

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Note: Please test scripts in Non Prod before trying in Production.
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