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Re: Increase frequency of log switches

From: Joel Garry <joel-garry_at_home.com>
Date: 8 Jul 2004 15:06:19 -0700
Message-ID: <91884734.0407081406.78a76cec@posting.google.com>


"Tom" <tomNOSPAM_at_teameazyriders.com> wrote in message news:<1089302964.20354.0_at_spandrell.news.uk.clara.net>...
> > First, if you are properly set up in archive log mode, have duplexed
> > redo log groups, and are taking regular backups, the amount of data
> > lost in the event of "a major machine failure" is already near zero,
> > and has nothing to do with the frequency of log switches.
> >
> > Second, the reason you don't find a parameter to control the maxsize
> > of a redo log before a switch is because there is none. You're redo
> > log files are a fixed size. A switch occurs when one fills up or you
> > manually issue ALTER SYSTEM SWITCH LOGFILE.
>
> Thanks - Yes i already have everything running as you state and can recover the whole instance onto a test machine.
>
> My query though is that if online redo has not been archived then this is not included in the backup. Therefore the time from last
> RMAN backup to failure could, in my case, be around a day. If i could have the online redo archived more often i would reduce this
> potential data loss.
>
> Seems i need to run ALTER SYSTEM SWITCH LOGFILE every couple of hours to make sure i minimise this loss. This is as i don't backup
> online redo as per the information i have found.
>
> FYI - when i say 'major machine failure' i mean the building burns down or all disks eat themselves at the same time. As i have
> archived logs, backup control files and RMAN backups being duplicated offsite then i can maintain minimal data loss providing i can
> reduce the time between log switches. Unless i have completely got the wrong end of the stick.
>
> thanks for all your help

You seem to understand it a bit better than Ed here (sorry Ed!). Pre-9, it is common on unix systems to run periodic logfile switches in cron to achieve a given time granularity. 'Bout time they added that lag parameter.

jg

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Received on Thu Jul 08 2004 - 17:06:19 CDT

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