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Tom Kyte

Thanks for the question, bsva@mailcity.com.

Asked: September 14, 2000 - 10:04 am UTC

Last updated: July 25, 2003 - 6:41 am UTC

Version: 8.0.4

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You Asked

Hi Tom

Would like to know if there is any standard formula for calculating the size of RBS, Tables and Log files. If so can you please let me know the usage of that.

Is there any recommended size for RBS, Log Files for small, medium and large db.

Thanks
Bala

and Tom said...

No, not really.

For RBS, we all have rules of thumb. Its an empirical thing.

See
</code> http://asktom.oracle.com/pls/asktom/f?p=100:11:::::P11_QUESTION_ID:233214228495
for the details.  I myself like to start with about 15 or so (depending on the number of concurrent transactions) rollback segments -- each with initial=next=1m and minextents=25, maxextents=100.  So I have 15 to 25 25meg rollback segments that can grow to 100meg each.  I'll shrink them before backups back down to 25meg.

For tables, then only real way to do this is to load some sample data. See
http://asktom.oracle.com/pls/asktom/f?p=100:11:::::P11_QUESTION_ID:302216525000 <code>
it also points to some doc that has formula's, but since everything is a varying string pretty much -- they are usually pretty far off from reality.


Log files - you size and resize (not really resize but create new and drop old) as part of tuning. the size of your redo affects performance more then anything else (eg: having too small redo will not prevent you from doing anything like having too small rollback would).

I like to start with (depending on the system) 3 25meg log files. This is for "moderate" systems. The goal (some people will say) is to have sufficient online redo log to get you through your busy period without wrapping around for about 15-20 minutes. Their size depends on how frequently you want to checkpoint and how large you want them. I've used 25meg, 100meg and 255meg. You can go larger but I've not done so.


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Comments

A reader, July 24, 2003 - 5:17 pm UTC

Hi Tom,

I have the following situation:
60Meg redo per day during 16 hours of busy activity in the database.

My idea is to set the online redo log like this:
4 groups, 2 members each, 2Meg for each member size.

This is the first time I have to set a very small database and this number sounds too small to me.
I know that online redos have a great impact in the performance and I would like to have your advice in this case.
Do you think 2Meg is too small even when (according with my calculations) it is going to let switch the log files every 30 minutes if the log file is not full before that time?
Or Should I set the size to 25M as you suggested in this posting even when I will generate 60 Meg of redo in the entire day?

Thanks in advance for any suggestion.

Tom Kyte
July 25, 2003 - 6:41 am UTC


60meg is tiny, your logic is sound.