RE: Please Help - ora error

From: Jon Walthour <jonw_at_fuse.net>
Date: Sat, 18 Aug 2001 09:22:32 -0700
Message-ID: <F001.00370298.20010818090549@fatcity.com>

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

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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Author: G, Subrahmanyam (CAP)
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Author: Hillman, Alex
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Author: Jon Walthour
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