| undo_retention [message #352924] |
Fri, 10 October 2008 04:44  |
vinniora
Messages: 56
Registered: October 2008
Location: Mumbai
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HI all....i m asking a question abt undo_retention
by default undo_retention is 900s and my database too have this value.this means that the undo segment will flushes out the data after 900s but when i fired a query
select begin_time,end_time,undoblks from v$undostat;
it is still showing the undoblks (having some value)of previous date..
so why it is showing these value..as retention time is only 900secs...plz help me out
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| Re: undo_retention [message #352932 is a reply to message #352927] |
Fri, 10 October 2008 05:01  |
vinniora
Messages: 56
Registered: October 2008
Location: Mumbai
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version is oracle 10g
thank you for the reply..this means tht it will not be flushed until some of the transaction may take up tht space...if not then it will remain there forever
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| Re: undo_retention [message #352945 is a reply to message #352924] |
Fri, 10 October 2008 05:28 |
vinniora
Messages: 56
Registered: October 2008
Location: Mumbai
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and could u please answer that...if it flushes only when it needed the space then why we are using undo_retention....
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| Re: undo_retention [message #352953 is a reply to message #352945] |
Fri, 10 October 2008 05:43 |
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Michel Cadot
Messages: 68666
Registered: March 2007
Location: Nanterre, France, http://...
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Senior Member
Account Moderator |
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1/ Yes data are not flushed after commit, this is the purpose of undo retention: to retain after commit
2/ undo retention, depending on RETENTION parameter of tablespace:
* when GUARANTEE, guarantees that the undo data earlier than retention time are not flushed
* when NOGUARANTEE, keep undo data earlier than retention time unless there is no more space for new transactions.
Regards
Michel
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