Determing the optimal UNDO tablespace size

###############Determing the optimal UNDO tablespace size############################################3


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#
) 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'
/



set feedback off
set heading off
set lines 132
declare
cursor get_undo_stat is
select d.undo_size/(1024*1024) "C1",
substr(e.value,1,25) "C2",
(to_number(e.value) * to_number(f.value) *
g.undo_block_per_sec) / (1024*1024) "C3",
round((d.undo_size / (to_number(f.value) *
g.undo_block_per_sec))) "C4"
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';
begin
dbms_output.put_line(chr(10)||chr(10)||chr(10)||chr(10) ||
'To optimize UNDO you have two choices :');
dbms_output.put_line('==================================================
==' || chr(10));
for rec1 in get_undo_stat loop
dbms_output.put_line('A)
Adjust UNDO tablespace size according to UNDO_RETENTION :'
|| chr(10));
dbms_output.put_line(rpad('ACTUAL UNDO SIZE ',65,'.')|| ' : ' ||
TO_CHAR(rec1.c1,'999999') || ' MEGS');
dbms_output.put_line(rpad('OPTIMAL UNDO SIZE WITH ACTUAL UNDO_RETENTION
(' || ltrim(TO_CHAR(rec1.c2/60,'999999'))
|| ' MINUTES)
',65,'.') || ' : ' || TO_CHAR(rec1.c3,'999999') || ' MEGS');
dbms_output.put_line(chr(10));
dbms_output.put_line('B) Adjust UNDO_RETENTION according to UNDO tablespace size :'
|| chr(10));
dbms_output.put_line(rpad('ACTUAL UNDO RETENTION ',65,'.') ||
' : ' || TO_CHAR(rec1.c2/60,'999999') || ' MINUTES');
dbms_output.put_line(rpad('OPTIMAL UNDO RETENTION WITH ACTUAL UNDO SIZE
(' || ltrim(TO_CHAR(rec1.c1,'999999')) || ' MEGS) ',65,'.') || ' : ' ||
TO_CHAR(rec1.c4/60,'999999') || ' MINUTES');
end loop;
dbms_output.put_line(chr(10)||chr(10));
end;
/


select 'Number of "ORA-01555 (Snapshot too old)" encountered since
the last startup of the instance : ' || sum(ssolderrcnt)
from v$undostat;