Re: UNDO: 10g-style behaviour in

From: Jonathan Lewis <>
Date: Sat, 18 Apr 2009 07:14:43 +0100
Message-ID: <>

"Randolf Geist" <> wrote in message On Apr 13, 10:16 am, "Jonathan Lewis" <> wrote:
> Randolf,
> i.e. the case when AutoExtend is ON - and my point was that I had seen
> the tuned_undoretention value in v$undostat drop BELOW the setting
> for parameter undo_retention with autoextend ON.


apologies, I got that wrong and thought it was about the "autoextend OFF" case. Your case seems to be odd, yes, and I would tend more to the "implementation bug" or "implementation limitation" explanation (given the "all available space tied to one large undo segment" information).



Confession time - I've just checked the notes I made at that client, and the comment I made above was wrong. I had two clients with undo problems in one week and mixed their configurations up when describing the anomaly.

I have NOT seen the tuned_undoretention drop below the parameter setting. The client with autoextensible files had (hence auto undo tuning) had simply let his undo_retention default to 900 seconds.

Querying his v$undostat, his tuned_undoretention had regularly climbed to 50,000 seconds then plunged to 1,500 seconds. (The other client had set his undo_retention to 14,400 seconds, and that's where I had muddled things up in my memory).

Client 1 has a problem because of side effects of the enormous automatic redistribution of undo extents that took place from time to time.


Jonathan Lewis

Author: Cost Based Oracle: Fundamentals

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Received on Sat Apr 18 2009 - 01:14:43 CDT

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