Re: Any performance issues for hot backups ??

Bas Ven wrote:
>
> I am looking into the possibilities Oracle can give me
> to do 'hot backups'. From a developers point of view I don't
> have to do anything, except require that the database is started
> in the ARCHIVELOG mode. (at least that is what I read so far,
> if I am wrong in this assumption, please let me know).
>
> I am pretty sure that when I write the above as a conclusion
> I will immediately be getting responses (from within my company)
> saying that this solution is not workable because of performance issues.
> Therefor I am asking this group for 'field' experiences. Are there
> any reports or does anyone have experience that indicates that the
> performance of the Oracle database degrades (significantly) or
> hardly affects it when running in archivelog mode ?
>
> Regards,
>
> Bas

Hi Bas,
we run all our databases in archivelog mode and I think most of others do so. The performance 'degration' may come from:

1. archivelog process must copy redologs to archivelog destination
2. bad redolog configuration
3. insufficient space on disk where archived logs reside

Some explanation:
1. I think Oracle uses OS copy-command to copy filled redolog and this is not CPU-intensive; a bit I/O is needed.
2. If all of your redologs fill up before arch-process copies them to arhived logs (and frees redolog up for reuse) then the writer-process (dbwr) will stop until space is available. To cure this simply add more redolog space (more files or make them bigger). In some cases you need to configure Oracle so that arch-process is more active. 3. You will need (disk)space to store archived redologs. If this space fills up, Oracle instance will hang up. To estimate the space needed you can look alert_<sid>.log file and see how often logswitch happens.

Summa summarum:
Use archivelog mode. If the basic configuration of db is OK (2 & 3 above) you will not see any difference in performance.

-- 

Timo Haatainen
Carelcomp Forest Oy