Re: MTTR and Optimal Logfile Size

How many logfile switches per hour occur at the heaviest switching hour? Here is a query that can help you find that information:

select trunc(first_time,'hh24'), count(*) from v$archived_log
where first_time >= sysdate - 30
group by trunc(first_time,'hh24')
order by 2;

Ideally you want a logfile switch about every 20 minutes (Oracle's documented best practice) and have your redo log files multiplexed. With current numbers provided this would be closer to 50GB.

Brent

On Thu, Jan 15, 2015 at 11:06 AM, Jeff C <backseatdba_at_gmail.com> wrote:

> I set my fast_start_mttr_target to 3600 to get a baseline but I noticed
> that it suggest the optimal logfile size to 8561mb which seems very high.
> Currently my logfile size is 50mb and I have been getting a some more
> frequent log switch than in the past so I was going to increase it. And I
> never had mttr set so I set it to see what it suggest. But why would it
> suggest an 8gb log file? If I have 3 groups that is 24 gigs of a logs for a
> 30gb database.
>
> Thanks,
> Jeff
>

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