Re: Guaranteed Flashback Table

From: Charlotte Hammond <>
Date: Thu, 1 May 2008 04:10:33 -0700 (PDT)
Message-ID: <>

Sorry, you're absolutely right - I've commited the oracle-l sin of forgetting to mention the version - I'm on 10gR2.

The problem I have with RETENTION GUARANTEE is that I've absolutely no idea how long the data manipulation will need - there's not just processing time but time involved in getting results manually checked, waiting for people to do this (who tend to wander off out of town when you most need them etc.) so I'm scared of setting too small a value that we can't then flash back, or too large a value that we blow out of disk space capturing lots of un-needed undo for the rest of the database not involved in this operation.

Flashback Archive sounds like it could be just the ticket - but no plans for 11g just yet. Thanks, though, I'll keep it in mind for the future!

Thank you,

  • Original Message ---- From: Robert Freeman <> To:; Cc: oracle-l <> Sent: Wednesday, April 30, 2008 11:20:53 PM Subject: Re: Guaranteed Flashback Table

OF course, she could be on 9iR1 and then none of this makes a difference! :-)  

Robert G. Freeman
Oracle Database 11g New Features (Oracle Press) Portable DBA: Oracle (Oracle Press)
Oracle Database 10g New Features (Oracle Press) Oracle9i RMAN Backup and Recovery (Oracle Press) Oracle9i New Feature
Blog: (Oracle Press)

  • Original Message ---- From: Stefan Knecht <> To: Cc: oracle-l <> Sent: Wednesday, April 30, 2008 3:16:56 PM Subject: Re: Guaranteed Flashback Table

Hi Charlotte

No need to go to 11g -- you can do this in 10gR2 as well -- take a look at the retention guarantee clause, which you can specifiy at tablespace level:


RETENTION GUARANTEE specifies that Oracle Database should preserve unexpired undo data in all undo segments of tablespace even if doing so forces the failure of ongoing operations that need undo space in those segments. This setting is useful if you need to issue an Oracle Flashback Query or an Oracle Flashback Transaction Query to diagnose and correct a problem with the data.



On Wed, Apr 30, 2008 at 10:01 PM, Charlotte Hammond <> wrote:

Hi All,

I'd like to have the option to flashback a few large-ish tables (NOT the whole database) to the start of a complex data manipulation operation. However I have no idea how long this operation will take so I have to set UNDO_RETENTION to a big value just to be sure. I'd prefer to be able to define a point at the start of the operation, and say "keep enough undo to go back here". Is there any such mechanism? (Only thing I could think of was to keep dynamically cranking up UNDO_RETENTION as the operation proceeds but that seems really messy).

I'll probably just stick with the tried and trusted CTAS "backup" of the tables before I start but just wanted to check that I'm not missing out on something that could save me time and space.

Any suggestions welcome - thanks!

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-- Received on Thu May 01 2008 - 06:10:33 CDT

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