Friday, November 16, 2007

Sizing the UNDO TABLESPACE for Automatic Undo management

Sizing an UNDO tablespace requires three pieces of data.

- (UR) UNDO_RETENTION in seconds
- (UPS) Number of undo data blocks generated per second
- (DBS) Overhead varies based on extent and file size (db_block_size)

UndoSpace = [UR * (UPS * DBS)] + (DBS * 24)

Two can be obtained from the initialization file: UNDO_RETENTION and DB_BLOCK_SIZE.
The third piece of the formula requires a query against the database. The number of undo blocks generated per second can be acquired from V$UNDOSTAT.

The following formula calculates the total number of blocks generated and divides it by the amount of time monitored, in seconds:

SQL>SELECT (SUM(undoblks))/ SUM ((end_time - begin_time) * 86400) FROM v$undostat;

Column END_TIME and BEGIN_TIME are DATE data types. When DATE data types are subtracted, the result is in days. To convert days to seconds, you multiply by 86400, the number of seconds in a day.

The result of the query returns the number of undo blocks per second. This value needs to be multiplied by the size of an undo block, which is the same size as the database block defined in DB_BLOCK_SIZE.

The following query calculates the number of bytes needed:

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 value from v$parameter where name
= 'undo_tablespace'));


Anonymous said...

what does the value 24 represents

Microsoft Office 2007 said...

NEVERTHELESS, THE CIVIL LAW is and must be neutral about who has a more noble or rewarding faith. The breakaway parishes ought to win every Office 2010facet of the lawsuit not becauseMicrosoft Office 2010 their beliefs or their politics are better, Microsoft wordbut because both lawOffice 2007and equity, along with common sense, are on Microsoft Officetheir side.Microsoft Office 2007 Not only does Virginia state law (the Division Statute)Office 2007 keyexplicitly apply to just such a Office 2007 downloadsituation as now exists, but the history Office 2007 Professionalespecially of The Falls Church argues against the claims of Outlook 2010the Virginia Diocese with which theyMicrosoft outlookhave disassociated.Microsoft outlook 2010First, The Falls Church wasWindows 7 founded, formed, and developed long before the diocese, or the national Episcopal Church, even existed.