Re: Flashback queries

Answers in-line

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

  The educated person is not the person
  who can answer the questions, but the
  person who can question the answers -- T. Schick Jr

One-day tutorials:
http://www.jlcomp.demon.co.uk/tutorial.html

Three-day seminar:
see http://www.jlcomp.demon.co.uk/seminar.html ____UK___November

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Wednesday, December 24, 2003 9:44 PM

> It's been awhile since I've looked at flashback queries, and
> I have a couple questions:
>
> * Given an SCN, is there any way to know for certain whether
> a flashback query to that SCN is possible? Can a non-DBA
> user determine this?
>

    No, not without doing it.
    As a general principle, you can always be in a position where     one querycan flash back to SCN = t1, but another query can't     because the two queries require undo from different segments.

> * Is there an easy way to determine how much undo data my
> database is (hopefully) retaining? In other words, can I
> easily determine how far back in the past I *can* go?
>

    No.

You could mess about with dumping segment header blocks and looking at the 'retention' table, which has a timestamp per extent of the most recent commit recorded against that extent. The highest (most recent) timestamp would be a valid bound for the earliest point in time that you could reach - but depending on luck, size of extents, etc. you might get some queries going a lot further back.

> Yes, here it is Christmas eve, and I'm working away...
>

> Best regards,
>
> Jonathan Gennick --- Brighten the corner where you are
> http://Gennick.com * 906.387.1698 * mailto:jonathan@gennick.com
>
> Join the Oracle-article list and receive one
> article on Oracle technologies per month by
> email. To join, visit

http://four.pairlist.net/mailman/listinfo/oracle-article,
> or send email to Oracle-article-request_at_gennick.com and
> include the word "subscribe" in either the subject or body.
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Jonathan Gennick
> INET: jonathan_at_gennick.com
>
> Fat City Network Services -- 858-538-5051 http://www.fatcity.com
> San Diego, California -- Mailing list and web hosting services
> ---------------------------------------------------------------------
> To REMOVE yourself from this mailing list, send an E-Mail message
> to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
> the message BODY, include a line containing: UNSUB ORACLE-L
> (or the name of mailing list you want to be removed from). You may
> also send the HELP command for other information (like subscribing).

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Jonathan Lewis
  INET: jonathan_at_jlcomp.demon.co.uk

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).