Reducing unused tablespace size

Question

Hi,
i have oracle database 10g on linux.
when i initially created tablespaces i allocated a huge amount of space, but when i checked the actual data size in eac tablespace, they are very small.
and now i want to backup my tablespaces in a tape drive. but the size of all the tablespace is bigger then my tape.
is there a way where i can reduce the size of my tablespaces. for example my "USERS" tablespace has only data occupying only 3 GB but i allocated about 10GB as the size for USERS tablespace.
so how can i bring the size down to 5GB so i do need to backup unnecessary space on my tape.
Thanks,
Philip.

Answer 1

Hi,
First run below query and according query output you can reduce you tablespace size.
ORA-03297: file contains used data beyond requested RESIZE value
SQL> select bytes/1024 from dba_data_files where file_id = 6;
BYTES/1024
7168
SQL> select sum(bytes/1024) from dba_segments where tablespace_name = 'EXAMPLE';
SUM(BYTES/1024)
5440
SQL> alter database
2 datafile 'c:\oracle\product\10.1.0\oradata\db02\example01.dbf' resize 5500k
alter database
ERROR at line 1:
ORA-03297: file contains used data beyond requested RESIZE value
According below query output you can reduce your tablespace size up to HWM.
if you want to reset HWM you can use 1.export + import OR alter table + rebuild index.
SQL> ed
Wrote file afiedt.buf
1 select
2 a.file_name,
3 a.bytes file_size_in_bytes,
4 (c.block_id+(c.blocks-1)) * &_BLOCK_SIZE HWM_BYTES,
5 a.bytes - ((c.block_id+(c.blocks-1)) * &_BLOCK_SIZE) SAVING
6 from dba_data_files a,
7 (select file_id,max(block_id) maximum
8 from dba_extents
9 group by file_id) b,
10 dba_extents c
11 where a.file_id = b.file_id
12 and c.file_id = b.file_id
13 and c.block_id = b.maximum
14* and c.tablespace_name = 'EXAMPLE'
SQL> /
Enter value for blocksize: 8192
old 4: (c.block_id+(c.blocks-1)) * &_BLOCK_SIZE HWM_BYTES,
new 4: (c.block_id+(c.blocks-1)) * 8192 HWM_BYTES,
Enter value for blocksize: 8192
old 5: a.bytes - ((c.block_id+(c.blocks-1)) * &_BLOCK_SIZE) SAVING
new 5: a.bytes - ((c.block_id+(c.blocks-1)) * 8192) SAVING
FILE_NAME
FILE_SIZE_IN_BYTES HWM_BYTES SAVING
C:\ORACLE\PRODUCT\10.1.0\ORADATA\DB02\EXAMPLE01.DBF
7340032 6356992 983040
SQL> alter database
2 datafile 'c:\oracle\product\10.1.0\oradata\db02\example01.dbf' resize 63569
92;
Database altered.regards
Taj