1. Anar Godjaev
Undo Management
optimal undo_retention parameter = actual undo size /
(db_block_size/undo_block_per_sec)
-- **********************
-- manual undo management
-- **********************
create rollback segment r01 tablespacerbs;
create public rollback_segment r01 tablespacerbs;
alter rollback segment r01 offline;
drop rollback segment r01;
-- *************************
-- automatic undo management
-- *************************
alter system set undo_management = auto;
alter system set undo_tablespace = <ts_name>;
alter system set undo_suppress_errors = true|false ;
alter system set undo_retention = 900; --seconds
select name, value from v$parameter where name like
'undo_management'
select name, value from v$parameter where name like
'undo_tablespace'
select name, value from v$parameter where name like
'undo_retention'
-- creating undo tablespace
create undo tablespacets_undodatafile 'C:ts_undo_01.dbf' size
20m;
alter tablespacets_undo add datafile 'C:ts_undo_02.dbf' size
40m;
alter system set undo_tablespace = ts_undo;
drop tablespacets_undo;
alter tablespacets_undo retention guarantee;
select retention, tablespace_name from dba_tablespaces;

2. Anar Godjaev
select begin_time, end_time, tuned_undoretention from
v$undostat;
-- calculating undo space
select
ceil(((UR * (UPS * DBS)) + (DBS * 24))/1024/1024) as MB
from
(select value as UR from v$parameter where
name='undo_retention'),
(select (sum(undoblks)/sum(((end_time - begin_time) * 84600)))
as UPS
from v$undostat),
(select value as DBS from v$parameter where name =
'db_block_size');
set transaction read only;
set transaction isolation level serializable; -- possible
negative impact on performance
-- Actual Undo Size
SELECT SUM(a.bytes) "UNDO_SIZE"
FROM v$datafile a,
v$tablespace b,
dba_tablespaces c
WHERE c.contents = 'UNDO'
AND c.status = 'ONLINE'
AND b.name = c.tablespace_name
AND a.ts# = b.ts#;
-- Undo Blocks per Second
SELECT MAX(undoblks/((end_time-begin_time)*3600*24))
"UNDO_BLOCK_PER_SEC"
FROM v$undostat;
-- DB Block Size
SELECT TO_NUMBER(value) "DB_BLOCK_SIZE [KByte]"
FROM v$parameter
WHERE name = 'db_block_size';

3. Anar Godjaev
-- optimal undo retention
SELECT d.undo_size/(1024*1024) "ACTUAL UNDO SIZE [MByte]",
SUBSTR(e.value,1,25) "UNDO RETENTION [Sec]",
ROUND((d.undo_size / (to_number(f.value) *
g.undo_block_per_sec)))
"OPTIMAL UNDO RETENTION [Sec]"
FROM (
SELECT SUM(a.bytes) undo_size
FROM v$datafile a,
v$tablespace b,
dba_tablespaces c
WHERE c.contents = 'UNDO'
AND c.status = 'ONLINE'
AND b.name = c.tablespace_name
AND a.ts# = b.ts#
) d,
v$parameter e,
v$parameter f,
( SELECT MAX(undoblks/((end_time-begin_time)*3600*24))
undo_block_per_sec FROM v$undostat ) g
WHERE e.name = 'undo_retention'
AND f.name = 'db_block_size';
-- optimal undo size
SELECT d.undo_size/(1024*1024) "ACTUAL UNDO SIZE [MByte]",
SUBSTR(e.value,1,25) "UNDO RETENTION [Sec]",
(TO_NUMBER(e.value) * TO_NUMBER(f.value) *
g.undo_block_per_sec) / (1024*1024)
"NEEDED UNDO SIZE [MByte]"
FROM (
SELECT SUM(a.bytes) undo_size
FROM v$datafile a,
v$tablespace b,
dba_tablespaces c
WHERE c.contents = 'UNDO'
AND c.status = 'ONLINE'
AND b.name = c.tablespace_name
AND a.ts# = b.ts#

4. Anar Godjaev
) d,
v$parameter e,
v$parameter f,
(
SELECT MAX(undoblks/((end_time-begin_time)*3600*24))
undo_block_per_sec
FROM v$undostat
) g
WHERE e.name = 'undo_retention'
AND f.name = 'db_block_size';
-- undo consumer sessions
SELECT
TO_CHAR (s.SID) || ',' || TO_CHAR (s.serial#) sid_serial,
NVL (s.username, 'None') orauser,
s.program,
r.NAME undoseg,
t.used_ublk * TO_NUMBER (x.VALUE) / 1024 || 'K' "Undo",
t1.tablespace_name
FROM
SYS.v_$rollname r,
SYS.v_$session s,
SYS.v_$transaction t,
SYS.v_$parameter x,
dba_rollback_segs t1
WHERE
s.taddr = t.addr
AND r.usn = t.xidusn(+)
AND x.NAME = 'db_block_size'
AND t1.segment_id = r.usn
AND t1.tablespace_name = 'UNDOTBS1';