ممكن حد يشرحلي المعادلة دي undo_tablespace_size = UR * UPS
عشان موش فاهمها خالص
ولكم مني جزيل الشكر والامتنان

UR is UNDO_RETENTION in seconds--------> take it as 500 secs

(UPS) is Number of undo data blocks generated per second Which can be calculated by following query


SELECT end_time,begin_time,undoblks FROM v$undostat;


(DBS) is Overhead varies based on extent and file size (db_block_size)






Sizing an UNDO Tablespace
Sizing an UNDO tablespace requires three pieces of data. 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
second can be acquired from V$UNDOSTAT. The following formula calculates the total
number of blocks generated and divides it by the amount of time monitored, in seconds:
SELECT (SUM(undoblks) / SUM( ((end_time - begin_time) * 86400)
FROM v$undostat;
Column END_TIME and BEGIN_TIME are DATE data types. When DATE data types
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
multiplied by the size of an undo block, which is the same size as the database block
in DB_BLOCK_SIZE. The following query calculates the number of bytes needed:


following quer calculates the undo segment size


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 value AS DBS
FROM v$parameter
WHERE name = 'db_block_size');
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