Space really used on TBS

Question

Hi,
executing the following query
SELECT b.tablespace_name, a.*,
TRUNC (a.segment_size / tbs_size * 100, 2) segment_perc_used,
b.tbs_freespace,
TRUNC (b.tbs_freespace / c.tbs_size * 100, 2) freespace_perc,
c.tbs_size
FROM (SELECT SUM (BYTES) / 1024 / 1024 segment_size
FROM dba_extents
WHERE tablespace_name = 'USER_CDC_DATA') a,
(SELECT tablespace_name, SUM (BYTES) / 1024 / 1024 tbs_freespace
FROM dba_free_space
WHERE tablespace_name = 'USER_CDC_DATA'
GROUP BY tablespace_name) b,
(SELECT tablespace_name, SUM (BYTES) / 1024 / 1024 tbs_size
FROM dba_data_files
WHERE tablespace_name = 'USER_CDC_DATA'
GROUP BY tablespace_name) c
I got this result
USER_CDC_DATA,112,0.72,5076.8125,32.75,15500
where 112Mb are used (0.72% of tbs total available space)
5076.8125 are free (32.75% of tbs total available space)
15500 is the tbs size
Why I have less then 1% used and only 32.75% free?
Where I'm wasting space?
Please note that shrink objects on tbs doesn't provide any benefit.
Regards
Mauro

Answer 1

Hi Mauro,
Where I'm wasting space?Perhaps it's space reserved by PCTFREE?
You can run scripts to "map your tablespace" and see space usage by block:
http://www.dba-oracle.com/data_warehouse/tablespace_reorganization.html
set linesize 132;
set pages 999;
rem set feedback off;
rem set verify off;
rem set heading off;
rem set termout off;
break on file_id skip page;
break on free skip 1;
compute sum of KB on free;
spool tsfrag;
column owner format a10;
column segment_name format a10;
column tablespace_name format a14;
column file_id format 99 heading ID;
column end format 999999;
column KB format 9999999;
column begin format 999999;
column blocks format 999999;
select
tablespace_name,
file_id,
owner,
segment_name,
block_id begin,
blocks,
block_id+blocks-1 end,
bytes/1024 KB,
'' free
from sys.dba_extents
where tablespace_name not in ('RBS','SYSTEM','TEMP','TOOLS','USER')
union
select
tablespace_name,
file_id,
'' owner,
'' segment_name,
block_id begin,
blocks,
block_id+blocks+1 end,
bytes/1023 KB,
'F' free
from sys.dba_free_space
where tablespace_name not in ('RBS','SYSTEM','TEMP','TOOLS','USER')
order by 1, 2, 5
Hope this helps. . .
Donald K. Burleson
Oracle Press author
Author of "Oracle Tuning: The Definitive Reference":
http://www.dba-oracle.com/bp/s_oracle_tuning_book.htm