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

Posted 2021-03-13 yaoyangding

 

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

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In this Document   Goal   Solution   References   APPLIES TO: Oracle Database - Enterprise Edition - Version 9.2.0.1 to 11.2.0.4 [Release 9.2 to 11.2] Oracle Database Cloud Schema Service - Version N/A and later Oracle Database Exadata Cloud Machine - Version N/A and later Oracle Cloud Infrastructure - Database Service - Version N/A and later Oracle Database Backup Service - Version N/A and later Information in this document applies to any platform. Oracle Server Enterprise Edition - Version: 9.2.0.1 to current release ***Checked for relevance on 04-Feb-2016*** GOAL To assist Database Administrators in sizing an UNDO Tablespace for automatic undo management. SOLUTION 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) The undo space needed is calculated as: UndoSpace = UR * (UPS * DBS) Two of the pieces of information can be obtained from the instance configuration: UNDO_RETENTION and DB_BLOCK_SIZE. The third piece of the formula requires a query being run against the database. The maximum number of undo blocks generated per second can be acquired from V$UNDOSTAT. Note: Overall consideration for peak/heavy vs. normal system activity should be taken into account when peforming the calculations. Autoextend OFF vs. ON will change the behavior for UNDO_RETENTION growth and use of UNEXPIRED extents. See Note 461480.1 for more information. The following formula calculates the peak undo blocks generated per second: SQL> SELECT undoblks/((end_time-begin_time)*86400) "Peak Undo Block Generation" FROM v$undostat WHERE undoblks=(SELECT MAX(undoblks) FROM v$undostat); Column END_TIME and BEGIN_TIME are DATE data types. When DATE data types are subtracted, the resulting value is the # of days between both dates. To convert days to seconds, you multiply by 86400, the number of seconds in a day (24 hours * 60 minutes * 60 seconds). The following query calculates the number of bytes needed to handle a peak undo activity: SQL> SELECT (UR * (UPS * DBS)) AS "Bytes"      FROM (SELECT value AS UR FROM v$parameter WHERE name = ‘undo_retention‘),           (SELECT undoblks/((end_time-begin_time)*86400) AS UPS            FROM v$undostat            WHERE undoblks = (SELECT MAX(undoblks) FROM v$undostat)),           (SELECT block_size AS DBS            FROM dba_tablespaces            WHERE tablespace_name = (SELECT UPPER(value) FROM v$parameter WHERE name = ‘undo_tablespace‘)); For 10g and Higher Versions where Tuned undo retention is being used,please use below query: SQL>SELECT (UR * (UPS * DBS)) AS "Bytes" FROM (select max(tuned_undoretention) AS UR from v$undostat), (SELECT undoblks/((end_time-begin_time)*86400) AS UPS FROM v$undostat WHERE undoblks = (SELECT MAX(undoblks) FROM v$undostat)), (SELECT block_size AS DBS FROM dba_tablespaces WHERE tablespace_name = (SELECT UPPER(value) FROM v$parameter WHERE name = ‘undo_tablespace‘));