Shrink Datafile Size!

Question

Dear All,
My database server 11gR1 is running on Linux operating system. The disk where my database exists is almost 80% used. I need to shrink datafile, is there any such option available.
When i take dump of my database it is like 3.5 GB but the database size shown in the space summary of oracle enterprise manager is like 22 GB while the tablespace shows only 20% free space in it.
What is the best possible way to perform this function? Kindly help me. If there is anything else you need to know kindly ask.
Regards, Imran Baig

Answer 1

Identify which tablespace has grown big.
It could be the tablespace which hold application tables or undo datafiles or temp datafiles.
If it is the tablespace which hold the application data, find which object is big (from dba_segments).
It could be like some table is created with 15Gb storage space and contain only 1Gb of data.
SQL> set serveroutput on
SQL> set pages 1000
SQL> set lines 160
SQL> DECLARE
  2      alc_bks     NUMBER;
  3      alc_bts     NUMBER;
  4      unsd_bks    NUMBER;
  5      unsd_bts    NUMBER;
  6      luefi       NUMBER;
  7      luebi       NUMBER;
  8      lub         NUMBER;
  9  BEGIN
10          DBMS_SPACE.UNUSED_SPACE (
11              segment_owner               => 'RNCRY'
12          ,   segment_name                => 'COMS'
13          ,   segment_type                => 'TABLE'
14          ,   total_blocks                => alc_bks
15          ,   total_bytes                 => alc_bts
16          ,   unused_blocks               => unsd_bks
17          ,   unused_bytes                => unsd_bts
18          ,   last_used_extent_file_id    => luefi
19          ,   last_used_extent_block_id   => luebi
20          ,   last_used_block             => lub
21          );
22
23  DBMS_OUTPUT.PUT_LINE('Allocated space = '|| alc_bts );
24  DBMS_OUTPUT.PUT_LINE('Actual used space = '|| unsd_bts );
25  EXCEPTION
26      WHEN OTHERS THEN
27          DBMS_OUTPUT.PUT_LINE(SUBSTR(SQLERRM,1,250));
28  END;
29  /
Allocated space = 8534360064
Actual used space = 46874624
PL/SQL procedure successfully completed.The COMS table was allocated around 8Gb but it has only 44Mb of data.
So in this case the space is wasted and you cannot resize the datafile as the space is already allocated to a table.
Identify these kind of objects and then either you can use the SHRINK SPACE command or re create the object with
only required storage space.
If all the the objects are small, then you should be able to resize the datafiles using the RESIZE command.
HTH