Alex:
This is a fallacy that's been around since Oracle 6. In actuality, one
wants to set the initial and next extents of a temporary tablespace to
the same size as the size of the average sort in memory to ensure that
most disk sorts can be accommodated within a single temporary tablespace
extent. This avoids the unnecessary overhead of extent allocation. You
can determine the size of the average disk sort with the following
query:
SELECT DECODE(disk_sorts, NULL, 0, 0, 0, ROUND((blocks_written *
block_size) / disk_sorts, 0)) AS avg_sort_size
FROM (SELECT VALUE AS disk_sorts
FROM sys.v_$sysstat
WHERE name = 'sorts (disk)')
, (SELECT NVL(SUM(fs.phyblkwrt), 0) AS blocks_written
FROM dba_data_files df
, sys.v_$filestat fs
, dba_tablespaces ts
WHERE df.file_id = fs.file#
AND df.tablespace_name = ts.tablespace_name
AND ts.contents = 'TEMPORARY')
, (SELECT TO_NUMBER(VALUE) AS block_size
FROM sys.v_$parameter
WHERE name LIKE 'db_block_size');
For example, I just ran this query against one of our production systems
and it said the average disk sort was 61,349,888 bytes. Now, if I set
sort_area_size to just 1M (1,048,576), then Oracle would have to do an
additional 58 extent allocations, if the extents are not already present
in a temporary tablespace, and would possibly increase the number of
multiblock reads necessary to fetch the data in merging together the
sorted result set.
For more information on this topic, take a look at Steve Adams' website
http://www.ixora.com.au.
Jon Walthour
-----Original Message-----
Alex
Sent: Friday, August 17, 2001 11:52 AM
To: Multiple recipients of list ORACLE-L
Are you sure enough to post an answer?
Alex Hillman
-----Original Message-----
Sent: Friday, August 17, 2001 2:45 AM
To: Multiple recipients of list ORACLE-L
Hi
In case of Temporary Tablespace the Initital segemnt and next segment
should be equal to the sort_area_size parameter.
bye
G.Subrahmanyam
-----Original Message-----
Sent: Thursday, August 16, 2001 8:28 PM
To: Multiple recipients of list ORACLE-L
Hello all,
I have a strage error.
'ORA-01658: unable to create INITIAL extent for segment in tablespace
TEMP'. The clients TEMP tablespace is 200M. The sql is:-
SELECT a.username, length(sql_text),
substr(sql_text,1,100) as "SQL TEXT",
substr(sql_text,101,250) as "Second TEXT",
substr(sql_text,351,250) as "Third TEXT",
substr(sql_text,601,250) as "Fourth TEXT",
substr(sql_text,851,250) as "Fifth TEXT",
substr(sql_text,1101,250) as "Sixth TEXT"
FROM sys.dba_users a, v$session, v$sqlarea
WHERE parsing_user_id=user_id AND address=sql_address(+)
ORDER BY executions desc
/
Can you please explain why I am getting this error and cannot run the
simple SQL statement?
Rgds,
raja
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