Re: Shrinking datafiles

From: Thomas Kyte <tkyte_at_us.oracle.com>
Date: Tue, 03 Aug 1999 14:45:08 GMT
Message-ID: <37a7feed.5369130@newshost.us.oracle.com>

A copy of this was sent to "as" <joe_at_isp.com> (if that email address didn't require changing) On Tue, 3 Aug 1999 13:09:00 +0200, you wrote:

>Is it possible to shrink a datafile? The scenario is as such - after a few
>months we have seen that our live tables are not going to grow anymore as we
>archive data to an archive database. We initially set the tables to a large
>initial extent but have dropped and imported them to new smaller tables. We
>have a lot more free space available in the tablespace but this is not
>needed.
>Is it possible to reclaim this space in the physical file system by
>shrinking the .dbf datafile???
>
>Thanking you in advance
>Andre
>

If you have 7.2 or up you can resize datafiles and shrink them. They cannot be shrunk past the last extent allocate in them -- it is possible therefore to have a 100meg datafile with 1meg of data in it and NOT be able to shrink it at all (the 1meg of data is at the 'end' of the file).

This script helps you find out what files are candidates for resizing, how small they can become and generates the needed DDL to shrink them:

set verify off
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(+)
/

column cmd format a75 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 /

it is written for use with sqlplus.

--
See http://govt.us.oracle.com/~tkyte/ for my columns 'Digging-in to Oracle8i'... Current article is "Part I of V, Autonomous Transactions" updated June 21'st

Thomas Kyte                   tkyte_at_us.oracle.com
Oracle Service Industries     Reston, VA   USA

Opinions are mine and do not necessarily reflect those of Oracle Corporation Received on Tue Aug 03 1999 - 09:45:08 CDT