Re: Fast roll-back


"astalavista" <nobody@xxxxxxxxxxx> wrote in message
news:4978dca3$0$15296$426a74cc@xxxxxxxxxxxxxxx
Hi,

Why, where a roll back occurred, it is faster
to reboot the database instead of waiting the end
of the roll-back ?

Thanks for your lights




You may be thinking of something like the following:

If a process issues a rollback; then all the rows it had
locked will stay locked until the entire rollback is complete.

If the session is killed or the database is restarted (before
the process commits its transaction) then smon handles the
rollback. But if some other user process needs to update
some of the inconsistent data, it can detect that it's looking
at blocks that are in need of rollback and perform a "localised"
rollback against just those blocks.

This means that killing a session (or in your extreme case bouncing
the database) can allow other work to resume faster than it could
if you waited for a process rollback to complete.

It's possible that in earlier versions of Oracle, this "localised" rollback
could take place only at database restart. In modern versions it can
happen after a "kill session". Of course, it won't necessarily be the
case that killing a session will help.


--
Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com

Author: Cost Based Oracle: Fundamentals
http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html

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


.

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