Can u please explain the difference between both the queries.

Question

col TABLESPACE_NAME format a15;
col MAXSPACE format 9999999;
col USEDSPACE format 999999;
col FREESPACE format 999999;
col "% Free Space" format a6;
select tablespace_name,
sum((((8192*maxextend)/1024)/1024)) maxspace,
((sum(bytes)/1024)/1024) usedspace,
(sum((((8192*maxextend)/1024)/1024)) - ((sum(bytes)/1024)/1024)) freespace,
round((((sum((((8192*maxextend)/1024)/1024)) - ((sum(bytes)/1024)/1024))*100)/sum((((8192*maxextend)/1024)/1024))))||
' %' "% Free Space"
from dba_data_files a,
sys.filext$ b
where a.file_id = b.file#(+)
group by tablespace_name;
AND
SELECT size_free_gb.tablespace_name,
SUM( size_free_gb.size_gb) SIZe_gb,
SUM( size_free_gb.free_gb) free_gb
FROM ( SELECT DFS.FREE_GB,
SUM(DDF.BYTES / 1024 / 1024 / 1024) SIZE_GB,
DDF.FILE_ID,
DDF.TABLESPACE_NAME
FROM (SELECT SUM(BYTES / 1024 / 1024 / 1024) FREE_GB, FILE_ID
FROM DBA_FREE_SPACE
GROUP BY FILE_ID) DFS,DBA_DATA_FILES DDF
WHERE DDF.FILE_ID = DFS.FILE_ID
GROUP BY DDF.FILE_ID, DDF.TABLESPACE_NAME, DFS.FREE_GB) size_free_gb
GROUP BY size_free_gb.tablespace_name;
Why maxextend in first query.... ?
Thanks in Advance..

Answer 1

Hi Vivek,
Please see if it explains.
Sample output of query1
===============
TABLESPACE_NAME MAXSPACE USEDSPACE FREESPACE % Free
CDCRPT_IDX                    4608            %   
LM_8M_IDX_01                  4096            %   
XDB                            256            %   
MDM_DAT                       1012            %   
SYSTEM                         800            %   
CPM_DAT            10240      5500      4740 46 % 
LM_128K_DAT_01     65536      6144     59392 91 %  Sample Output of query2
===============
TABLESPACE_NAME                   SIZE_GB    FREE_GB
LM_8M_IDX_01                            4     2.8125
CDCRPT_IDX                            4.5 4.22113037
MDM_DAT                         .98828125 .538330078
XDB                                   .25 .203491211
SYSTEM                             .78125 .243713379
LM_128K_DAT_01                          6 3.96582031
CPM_DAT                        5.37109375 .469665527
CPM_IDX                           6.59375 2.86303711Your 1st query will hold true only for datafiles which are AUTOEXTENSIBLE, because the table SYS.FILEXT$ holds entry for those file_ids (datafiles) which has AUTOEXTENSIBLE as YES in DBA_DATA_FILES. If all your datafiles of all tablespaces are AUTOEXTENSIBLE (YES), then you should get entry like
CPM_DAT 10240 5500 4740 46 %.
Now, maxspace is calculated as sum((((8192*maxextend)/1024)/1024)) from table SYS.FILEXT$. maxextend signifies the maximum number of blocks that a file_id (datafile) can extend upto. That is, as the datafile is AUTOEXTENSIBLE, it has been allocated a minimum extend initially and then it can INCREMENT BY some particular EXTENTs until it reach MAX EXTENTS. So, this maxentend denote the same. Now if your database is using 8K block size (show parameter DB_BLOCK_SIZE), then we can get the maximum size of the datafile it can grow upto by using 8192*maxextend, and converted to MB (/1024/1024).
USEDSPACE and SIZE_GB calculated sam way using SUM(BYTES) from dba_data_files, just one is in MB and another in GB.
FREESPACE in 1st query is calculated as MAXSPACE - USEDSPACE, that is, space available for the file_id(datafile) to grow until reached maxextend. That is, we can guarantee that the datafile will not throw error until this value is reached and can be used out of the operating system disk space. It doesn't signify the free space for the datafile available in DB. FREE_GB in 2nd query signifies that.
% FREE is usual.
Thanks,
Tapan
Edited by: TapanKumar Saha on Apr 2, 2013 1:13 AM