Home » RDBMS Server » Server Administration » undo_retention (linux)
undo_retention [message #352924] Fri, 10 October 2008 04:44 Go to next message
vinniora
Messages: 56
Registered: October 2008
Location: Mumbai
Member
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
Re: undo_retention [message #352927 is a reply to message #352924] Fri, 10 October 2008 04:53 Go to previous messageGo to next message
Michel Cadot
Messages: 64140
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
Quote:
this means that the undo segment will flushes out the data after 900s

No, it means Oracle will flush if it needs space.
In addition, there were bugs in 9i (you didn't post your version when it is requested) that leads Oracle to not do it.

Regards
Michel
Re: undo_retention [message #352932 is a reply to message #352927] Fri, 10 October 2008 05:01 Go to previous messageGo to next message
vinniora
Messages: 56
Registered: October 2008
Location: Mumbai
Member
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
Re: undo_retention [message #352934 is a reply to message #352932] Fri, 10 October 2008 05:05 Go to previous messageGo to next message
Michel Cadot
Messages: 64140
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
Yes, this is the case.
Query the %BLKS columns of v$undostat.

Regards
Michel

[Updated on: Fri, 10 October 2008 05:05]

Report message to a moderator

Re: undo_retention [message #352938 is a reply to message #352924] Fri, 10 October 2008 05:15 Go to previous messageGo to next message
vinniora
Messages: 56
Registered: October 2008
Location: Mumbai
Member
ok...but will undodata still remain after commit???
Re: undo_retention [message #352945 is a reply to message #352924] Fri, 10 October 2008 05:28 Go to previous messageGo to next message
vinniora
Messages: 56
Registered: October 2008
Location: Mumbai
Member
and could u please answer that...if it flushes only when it needed the space then why we are using undo_retention....
Re: undo_retention [message #352953 is a reply to message #352945] Fri, 10 October 2008 05:43 Go to previous message
Michel Cadot
Messages: 64140
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
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
Previous Topic: How the HWM move?
Next Topic: what is the unit time in oracle??
Goto Forum:
  


Current Time: Fri Dec 09 04:25:03 CST 2016

Total time taken to generate the page: 0.07091 seconds