Re: Question on NEXT_CHANGE#

From: Riyaj Shamsudeen <riyaj.shamsudeen_at_gmail.com>
Date: Mon, 30 Dec 2013 11:56:02 -0800
Message-ID: <CAA2DszxtXO5CF9860V8JVpNe-OSCchoz=-=OJ2zLZ96xJG73fA_at_mail.gmail.com>

AFAIK, there are numerous actions that can allocate new SCNs, SCNs can be allocated with no redo records as well, and multiple redo records can be created at an SCN. Majority of those actions (that do not have redo associated) centered around control file accesses (as Jonathan pointed out). As a test, watch 'calls to kcmgas' statistics of a session and execute 'select * from v$database' from that watched session. You will see that every execution will increase that statistics.

BTW, kcmgas is the internal function to allocate new SCN. Another test would be compare the increase in the 'calls to kcmgas' statistic and number of unique SCNs in the archivelog file. In RAC, SCN allocation rate is higher to maintain cluster coherency.

SCN allocation rate increases sharply during hot backup too.

Cheers

Riyaj Shamsudeen
Principal DBA,
Ora!nternals - http://www.orainternals.com - Specialists in Performance, RAC and EBS
Blog: http://orainternals.wordpress.com/ Oracle ACE Director and OakTable member <http://www.oaktable.com/>

Co-author of the books: Expert Oracle
Practices<http://tinyurl.com/book-expert-oracle-practices/> , Pro Oracle SQL, <http://tinyurl.com/ahpvms8> <http://tinyurl.com/ahpvms8>Expert
RAC Practices 12c. <http://tinyurl.com/expert-rac-12c> Expert PL/SQL practices <http://tinyurl.com/book-expert-plsql-practices>

<http://tinyurl.com/book-expert-plsql-practices>

On Mon, Dec 30, 2013 at 9:00 AM, Phil Jones <phil_at_phillip.im> wrote:

> All,
>
> I think this all boils down to the usual question we're all asked when
> designing software/DB schemas.
>
> Do you want the numbers to be unique (with possible gaps) or truly
> sequential?
>
> The database is working correctly, probably using the missing scn numbers
> internally - it doesn't matter, but it would be interesting to know why.
>
> Cheers,
>
> Phil
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

--
http://www.freelists.org/webpage/oracle-l

Received on Mon Dec 30 2013 - 20:56:02 CET