Finding watermark: problem in linking dba_free_space and dba_data_files

Question

Hi all,
I'm trying to write a very simple (maybe too much simple...) query to find out how much space I can save doing a resize of my datafiles.
For this purpose, for every datafile, I look for the last free segment in the dba_free_space: if I find a row in dba_free_space such that the value (block_id+blocks-1) matches the one in dba_data_files.blocks, I can find the watermark.
The problem is that I have an (almost) empty tablespace with the last blocks unused: if I look in the dba_segments or in the dba_extents I can see that the last 5 or 4 blocks are not used, and they are not included in the dba_free_space.
So, here is my query:
select t.tablespace_name,
d.bytes / 1024 / 1024 as file_size_mb,
(f.block_id - 1) / d.blocks * d.bytes / 1024 / 1024 as space_before_watermark_mb,
f.bytes / 1024 / 1024 as space_after_watermark_mb,
d.file_name
from dba_tablespaces t, dba_data_files d, dba_free_space f
where t.tablespace_name = d.tablespace_name
and d.file_id = f.file_id
and d.blocks = (f.block_id + f.blocks - 1)
order by tablespace_name;
There are two problems right now:
- I have to use a different query to find out if there are datafiles whose last blocks are used
- I'm not able to find out informations about datafile whose last blocks are not used and are not in the dba_free_space.
How can I solve that?
thansk in advance for every comment

Answer 1

hi,
try the following to look for the HWM.
set serveroutput on
execute dbms_output.enable(2000000);
declare
cursor c_dbfile is
select tablespace_name
,file_name
,file_id
,bytes
from sys.dba_data_files
where status !='INVALID'
order by tablespace_name,file_id;
cursor c_space(v_file_id in number) is
select block_id,blocks
from sys.dba_free_space
where file_id=v_file_id
order by block_id desc;
blocksize binary_integer;
filesize binary_integer;
extsize binary_integer;
begin
/* get the blocksize of the database, needed to calculate the startaddress */
select value
into blocksize
from v$parameter
where name = 'db_block_size';
/* retrieve all datafiles */
for c_rec1 in c_dbfile
loop
filesize := c_rec1.bytes;
<<outer>>
for c_rec2 in c_space(c_rec1.file_id)
loop
extsize := ((c_rec2.block_id - 1)*blocksize + c_rec2.blocks*blocksize);
if extsize = filesize
then
filesize := (c_rec2.block_id - 1)*blocksize;
else
/* in order to shrink the free space must be uptil end of file */
exit outer;
end if;
end loop outer;
if filesize = c_rec1.bytes
then
dbms_output.put_line('Tablespace: '
||' '||c_rec1.tablespace_name||' Datafile: '||c_rec1.file_name);
dbms_output.put_line('Can not be resized, no free space at end of file.')
dbms_output.put_line('.');
else
if filesize < 2*blocksize
then
dbms_output.put_line('Tablespace: '
||' '||c_rec1.tablespace_name||' Datafile: '||c_rec1.file_name);
dbms_output.put_line('Has a highwater mark of: '||2*blocksize
||' Bytes, actual size: '||c_rec1.bytes||' Bytes');
dbms_output.put_line('.');
else
dbms_output.put_line('Tablespace: '
||' '||c_rec1.tablespace_name||' Datafile: '||c_rec1.file_name);
dbms_output.put_line('Has a highwater mark of: '||filesize
||' Bytes, actual size: '||c_rec1.bytes);
dbms_output.put_line('.');
end if;
end if;
end loop;
end;
regards
Alan