How to shrink Datafiles and Reclaim unused Space in Oracle

In this article we will discuss about shrinking datafiles to reclaim unused space in an Oracle database. Below are the scripts to release free space from the datafiles residing on ASM as well as disk. It will work for Oracle 11g, 12c 19c etc.

ORA-1652: unable to extend temp segment by 128 in tablespace TEMP

There are below of the some reasons due to which tablespace can grown excessively :

1. Lack of maintenance activity:   If you haven’t scheduled the purging script based on the retention period then table size can grow excessively and this will cause tablespace to grow unexpectedly and once the data is purged, datafile contain unused space that needs to be reclaimed.
2. Backup tables or other tables moved to different tablespace and left behind free unused space into the previous tablespace. 

How to Reclaim unused space from the Datafiles?

Below are two scripts using which you can reclaim unused space from the datafiles. You can use any of the below scripts but personally i like the 1st one.

SCRIPT 1: 

--NOTE: Run the below three select statement one by one --
set verify off
set pages 1000
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

--To Check Database block size:--
column value new_val blksize
select value from v$parameter where name = 'db_block_size'
/

-- To check how much space can be reclaimed --
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(+)
/

--Script to reclaim unused space from the datafiles of respective tablespace--
set pages 0
set lines 300
column cmd format a300 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
/

SCRIPT 2: 

REM Script is meant for Oracle version 9 and higher
REM -----------------------------------------------
 
set serveroutput on
exec dbms_output.enable(1000000);
 
declare
 
cursor c_dbfile is
select f.tablespace_name,f.file_name,f.file_id,f.blocks,t.block_size
,decode(t.allocation_type,'UNIFORM',t.initial_extent/t.block_size,0) uni_extent
,decode(t.allocation_type,'UNIFORM',(128+(t.initial_extent/t.block_size)),128) file_min_size
from dba_data_files f,
dba_tablespaces t
where f.tablespace_name = t.tablespace_name
and t.status = 'ONLINE'
order by f.tablespace_name,f.file_id;
 
cursor c_freespace(v_file_id in number) is
select block_id, block_id+blocks max_block
from dba_free_space
where file_id = v_file_id
order by block_id desc;
 
/* variables to check settings/values */
dummy number;
checkval varchar2(10);
block_correction number;
 
/* running variable to show (possible) end-of-file */
file_min_block number;
 
/* variables to check if recycle_bin is on and if extent as checked is in ... */
recycle_bin boolean:=false;
extent_in_recycle_bin boolean;
 
/* exception handler needed for non-existing tables note:344940.1 */
sqlstr varchar2(100);
table_does_not_exist exception;
pragma exception_init(table_does_not_exist,-942);
 
/* variable to spot space wastage in datafile of uniform tablespace */
space_wastage number;
 
begin
 
/* recyclebin is present in Oracle 10.2 and higher and might contain extent as checked */
begin
select value into checkval from v$parameter where name = 'recyclebin';
if checkval = 'on'
then
recycle_bin := true;
end if;
exception
when no_data_found
then
recycle_bin := false;
end;
 
/* main loop */
for c_file in c_dbfile
loop
/* initialization of loop variables */
dummy :=0;
extent_in_recycle_bin := false;
file_min_block := c_file.blocks;
 
begin
 
space_wastage:=0; /* reset for every file check */
 
<>
 
for c_free in c_freespace(c_file.file_id)
loop
/* if blocks is an uneven value there is a need to correct
with -1 to compare with end-of-file which is even */
block_correction := (0-mod(c_free.max_block,2));
if file_min_block = c_free.max_block+block_correction
then
 
/* free extent is at end so file can be resized */
file_min_block := c_free.block_id;
 
/* Uniform sized tablespace check if space at end of file
is less then uniform extent size */
elsif (c_file.uni_extent !=0) and ((c_file.blocks - c_free.max_block) < c_file.uni_extent)
then
 
/* uniform tablespace which has a wastage of space in datafile
due to fact that space at end of file is smaller than uniform extent size */
 
space_wastage:=c_file.blocks - c_free.max_block;
file_min_block := c_free.block_id;
 
else
/* no more free extent at end of file, file cannot be further resized */
exit check_free;
end if;
end loop;
end;
 
/* check if file can be resized, minimal size of file 128 {+ initial_extent} blocks */
if (file_min_block = c_file.blocks) or (c_file.blocks <= c_file.file_min_size)
then
 
dbms_output.put_line('Tablespace: '||c_file.tablespace_name||' Datafile: '||c_file.file_name);
dbms_output.put_line('cannot be resized no free extents found');
dbms_output.put_line('.');
 
else
 
/* file needs minimal no of blocks which does vary over versions,
using safe value of 128 {+ initial_extent} */
if file_min_block < c_file.file_min_size
then
file_min_block := c_file.file_min_size;
end if;
 
 
dbms_output.put_line('Tablespace: '||c_file.tablespace_name||' Datafile: '||c_file.file_name);
dbms_output.put_line('current size: '||(c_file.blocks*c_file.block_size)/1024||'K'||' can be resized to: '||round((file_min_block*c_file.block_size)/1024)||'K (reduction of: '||round(((c_file.blocks-file_min_block)/c_file.blocks)*100,2)||' %)');
 
 
/* below is only true if recyclebin is on */
if recycle_bin
then
begin
sqlstr:='select distinct 1 from recyclebin$ where file#='||c_file.file_id;
execute immediate sqlstr into dummy;
 
if dummy > 0
then
 
dbms_output.put_line('Extents found in recyclebin for above file/tablespace');
dbms_output.put_line('Implying that purge of recyclebin might be needed in order to resize');
dbms_output.put_line('SQL> purge tablespace '||c_file.tablespace_name||';');
end if;
exception
when no_data_found
then null;
when table_does_not_exist
then null;
end;
end if;
dbms_output.put_line('SQL> alter database datafile '''||c_file.file_name||''' resize '||round((file_min_block*c_file.block_size)/1024)||'K;');
 
if space_wastage!=0
then
dbms_output.put_line('Datafile belongs to uniform sized tablespace and is not optimally sized.');
dbms_output.put_line('Size of datafile is not a multiple of NN*uniform_extent_size + overhead');
dbms_output.put_line('Space that cannot be used (space wastage): '||round((space_wastage*c_file.block_size)/1024)||'K');
dbms_output.put_line('For optimal usage of space in file either resize OR increase to: '||round(((c_file.blocks+(c_file.uni_extent-space_wastage))*c_file.block_size)/1024)||'K');
end if;
 
dbms_output.put_line('.');
 
end if;
 
end loop;
 
end;
/