Re: Sizing Undo tablespace

From: hrishy <>
Date: Wed, 8 Jul 2009 07:27:54 +0000 (GMT)
Message-ID: <>

Hi Karl

Thanks for the script.
According to the script i need a undo tablespace with a size of 34Mb. However past few days through my monitoring script i am getting a errro message saying my undo tablespace is above 90% full.

And i ran another script to find undo hoggers SELECT TO_CHAR(begin_time, 'DD-MON-RR HH24:MI'),
          TO_CHAR(end_time, 'DD-MON-RR HH24:MI'),
          maxquerylen, maxqueryid,UNDOBLKS
FROM v$undostat
ORDER BY end_time

and this gives me a sqlid (maxqueryid) where the undoblks value is 13841.

Should i start tuning the query in question ?

  • On Wed, 8/7/09, Karl Arao <> wrote:

From: Karl Arao <>
Subject: Re: Sizing Undo tablespace
Date: Wednesday, 8 July, 2009, 8:12 AM

Hi Hrishy,

You could check this Metalink Note...

How To Size UNDO Tablespace For Automatic Undo Management
      Doc ID:     262066.1

You'll get from the note the query below:

SQL> SELECT (UR * (UPS * DBS)) + (DBS * 24) AS "Bytes" FROM (SELECT value AS UR FROM v$parameter WHERE name = 'undo_retention'),

(SELECT (SUM(undoblks)/SUM(((end_time - begin_time)*86400))) AS UPS FROM v$undostat), 
(select block_size as DBS from dba_tablespaces where tablespace_name= 
(select upper(value) from v$parameter where name = 'undo_tablespace'));

On Wed, Jul 8, 2009 at 2:50 PM, hrishy <> wrote:


I am trying to size my undo tablepsace by looking at the undo rates.i.e the column UNDOBLKS in v$undostat.

Value for undoblks for particular sql is 13841 and my database size is 8kb.Does this mean that i need to have a undo tablespace size of

select 8192*13841/1024/1024 from dual
108Gb ?

Not the particular sql does a corelated update of mere  72762 rows and the figure of 108Gb doesnt make much sense .This is a JDBC app and i dont have much idea if this sql is in some for loop or something.



Received on Wed Jul 08 2009 - 02:27:54 CDT

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