APPLIES TO:
Oracle Database - Enterprise Edition - Version 9.0.1.0 and laterInformation in this document applies to any platform.
***Checked for relevance on 06-Aug-2016***
GOAL
We need to reduce Disk usage at OS level . The first step for that will be to identify the HWM of datafile . The HWM specifies the limit to which you can resize a datafile.
SOLUTION
Script for MAX-Shrink:-
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
column value new_val blksize
select value from v$parameter where name = 'db_block_size';
/
select file_name,
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 ) smallest,
ceil( blocks*&&blksize/1024/1024) currsize,
ceil( blocks*&&blksize/1024/1024) -
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 ) savings
from dba_data_files a,
( select file_id, max(block_id+blocks-1) hwm
from dba_extents
group by file_id ) b
where a.file_id = b.file_id(+) order by savings desc
/
In lower versions you can use below query to find out possible savings from each data files of Database.
set linesize 400
col tablespace_name format a15
col file_size format 99999
col file_name format a50
col hwm format 99999
col can_save format 99999
SELECT tablespace_name, file_name, file_size, hwm, file_size-hwm can_save
FROM (SELECT /*+ RULE */ ddf.tablespace_name, ddf.file_name file_name,
ddf.bytes/1048576 file_size,(ebf.maximum + de.blocks-1)*dbs.db_block_size/1048576 hwm
FROM dba_data_files ddf,(SELECT file_id, MAX(block_id) maximum FROM dba_extents GROUP BY file_id) ebf,dba_extents de,
(SELECT value db_block_size FROM v$parameter WHERE name='db_block_size') dbs
WHERE ddf.file_id = ebf.file_id
AND de.file_id = ebf.file_id
AND de.block_id = ebf.maximum
ORDER BY 1,2);
Example: Sample Output of above query:-
Size Current Poss.
FILE_NAME Poss. Size Savings
-------------------------------------------------- -------- -------- --------
/u01/oradata/cp_jrnl_idx3.dbf 13,697 32,708 19,011
/u01/oradata/cp_jrnl_idx2.dbf 13,761 32,748 18,987
/u01/oradata/cp_jrnl_idx1_01.dbf 13,953 32,748 18,795
/u01/oradata/cp_jrnl_idx1.dbf 13,953 32,728 18,775
/u01/oradata/cp_jrnl_idx3_02.dbf 15,681 32,738 17,057
/u01/oradata/cp_jrnl_idx3_03.dbf 15,681 32,718 17,037
/u01/oradata/psindex_01.dbf 11,285 26,718 15,433
/u01/oradata/cp_jrnl_idx4.dbf 22,913 32,728 9,815
/u01/oradata/cpled_2010_1.dbf 7,721 10,858 3,137
/u01/oradata/cpled_2009_1.dbf 4,745 6,828 2,083
/u01/oradata/cpled_2008_1.dbf 4,873 6,948 2,075
/u01/oradata/cpled_2009_2.dbf 4,825 6,728 1,903
/u01/oradata/cpled_idx_1.dbf 19,905 21,000 1,095
--------
sum 145,203
By the output we can reclaim space around 141gb of space, without reorganizing any objects
Resize Datafiles:-
We can resize datafile up to “Smallest Size Poss” value (or) we can assign any fixed size (or) On top of that we can enable autoextend up to maximum size of datafile.
alter database datafile '/u01/oradata/cp_jrnl_idx3.dbf' autoextend on next 10m maxsize 32767m;
After resizing datafile, Possible savings recorded is around 19GB.
Execute above Script to check changes after resizing of datafiles:-
Size Current Poss.
FILE_NAME Poss. Size Savings
-------------------------------------------------- -------- -------- --------
/u01/oradata/cp_jrnl_idx3.dbf 13,697 13,700 3
/u01/oradata/cp_jrnl_idx2.dbf 13,761 13,770 9
/u01/oradata/cp_jrnl_idx1_01.dbf 13,953 13,970 17
/u01/oradata/cp_jrnl_idx1.dbf 13,953 13,970 17
/u01/oradata/cp_jrnl_idx3_02.dbf 15,681 15,690 9
/u01/oradata/cp_jrnl_idx3_03.dbf 15,681 15,690 9
/u01/oradata/psindex_01.dbf 11,285 11,300 15
/u01/oradata/cp_jrnl_idx4.dbf 22,913 22,920 7
/u01/oradata/cpled_2010_1.dbf 7,721 7,730 9
/u01/oradata/cpled_2009_1.dbf 4,745 4,750 5
/u01/oradata/cpled_2008_1.dbf 4,873 4,900 27
/u01/oradata/cpdevdb/cpled_2009_2.dbf 4,825 4,850 25
/u01/oradata/cpdevdb/cpled_idx_1.dbf 19,905 19,910 5
--------
sum 157
In earlier output possible savings is 141gb, Now possible savings is 157mb, So we reclaimed ~141gb of space at OS level.