????AUM????? undo ?????Automatic Undo Management??????????????á????????????????彫???????????????????????????? UNDO_RETENTION ?????????????λ???塣????? 900 ??? 15 ?????
?????????????????? undo ?????д???????????????????????????????????????
???????????1???????????? undo ?????С??
?????? Oracle 10g ????????????????? GUARANTEE ?????????????? undo_retention ???????undo ????????????
????UNDO?????С????????????
????(UR)UNDO_RETENTION ??λ??
????(UPS)????????undo ?????????
????(DBS)????????????????СDB_BLOCK_SIZE
?????????
????UndoSpace=UR*(UPS*DBS)
????????UNDO_RETENTION ?? DB_BLOCK_SIZE??????????????????????ò???????л????
??????????????UPS???????????????????V$UNDOSTAT?л??
????????????(UPS)????????undo ?????????.
????SQL> SELECT undoblks/((end_time-begin_time)*86400) "Peak Undo Block Generation"
????FROM v$undostat WHERE undoblks=(SELECT MAX(undoblks) FROM v$undostat);
??????????END_TIME and BEGIN_TIME ?????????????????????(24 hours * 60 minutes * 60 seconds).
?????????SQL?????UNDO?????С
SQL> SELECT (UR * (UPS * DBS)) AS "Bytes"
FROM (SELECT value AS UR FROM v$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$parameter WHERE name = 'undo_tablespace'));
????10g ??10g ?????汾????????????????:
SQL>SELECT (UR * (UPS * DBS)) AS "Bytes"
FROM (select max(tuned_undoretention) AS UR from v$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'));