Re: Frequency of log switches

Kurt-Erich Finger wrote:

>
> Howard,
>
> yesterday evening I stopped archiving for my test database.
> The log switches were back to 'normal' frequency. Which means one log
> switch per
> 12hrs. Since nobody is using this instance that's what I would
> exspect.
> I used log miner as described in the Administarator Guide and found
> 7000 records in $logmnr_contents when archiving was on, but
> 22000 records when archiving was off.
> In both cases I only found entries for user SYS (SYS.SNAP,SYS.JOB
> etc.) and INTERNAL operations.
>
> What could be the reason for this strange behavior?
> (I also searched metalink but couldn't find anything)
>
> Cheers
> Kurt-Erich

Well, that's good we've got some hard information. What's this SYS.SNAP and SYS.JOB? Are you running jobs? If so, then you have *something* generating redo, even though you say 'nobody' is using the instance... a job counts as somebody!

But it makes no sense for the *amount* of redo to be generated by a job to suddenly increase X-fold, just because you are in archivelog mode. Unless, as another poster mentioned, you happen to also have tablespaces in hot backup mode (because then, the first change that's made to a block causes the entire block to be written to redo, and not just the normal record-based before- and after-images. I've seen the quantity of redo increase by a factor of 30 under certain circumstances when hot backup is enabled).

So, to check that: what does a select * from v$backup; say??

Regards
HJR

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