Re: archivelog performance issues

From: Andrew Kerber <andrew.kerber_at_gmail.com>
Date: Tue, 7 Jul 2009 12:42:32 -0500
Message-ID: <ad3aa4c90907071042g16b78eabiea8f55ce48ea7e1d_at_mail.gmail.com>



Uh, Yes. If you are not in archive log mode, the redo log is not copied to the archivelog, so there is no overhead on the switch. When you are not in archive log mode, you just switch to the next redo log and keep going, overwriting what was in the log previously.

On Tue, Jul 7, 2009 at 12:23 PM, Richard Croasmun <rac_oracledba_at_msn.com>wrote:

>
> On Tue, 7 Jul 2009 12:31:43 -0400 Mark.Bobak_at_proquest.com wrote:
>
>
> Some things to check before you switch to archive log mode:
>
>
>
> - How frequently are you seeing log switches, at peak
> load time?
>
>
>
> Size your online redo so that you get a switch about every
> 15-30 minutes, at peak.
>
> If your load variaes greatly from peak to non-peak, you
> may want to use
>
> archive_lag_target to get more frequent switches during
> off-peak times.
>
>
>
> - Make sure you have at least three redo log groups.
>
>
>
> I agree 100% with those that state log archive mode should be based on
> recoverability, not performance. In addition, from a performance point of
> view, it seems to me that the only additional overhead is a copy of the
> online redo log to an archive log for each log switch. I would say that all
> the points about log size, frequency of log switches, number of online logs
> etc would apply even when the DB is NOT in archive log mode. The only
> exception would be having enough online logs (or large enough logs) such
> that the copy of a particular log finishes before the database wants to use
> that online redo log again. Obviously, if the DB is in archive log mode,
> the overhead of the copy on the DB could be reduced by placing the archive
> logs on separate disks from the database and online logs to minimize I/O
> contention. An last, but not least, don't let the archive log area fill
> up!! ;-) Am I missing anything here?
>
>
>
> Rick
>
>
>
>

-- 
Andrew W. Kerber

'If at first you dont succeed, dont take up skydiving.'

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Received on Tue Jul 07 2009 - 12:42:32 CDT

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