RE: redo log timing

The reason I proposed the question is the rule seems to deal with databases which have a constant transaction rate. Ours are highly variable. I've gone with keeping the median within 15 and 30 minutes. Our logs are 200MB and can switch as often as a once per minute to as seldom as once every 3 hours. I am familiar with all the benefits and drawbacks of small and large redo logs. I also assume that a catastrophic lost of the online acrtive redo log which is taking three hours to fill is no worse that losing one which takes less than a minute to fill.

I don't compress the archives, I back them up and then delete them via cron; not necessarily the best approach.

Ian MacGregor
Stanford Linear Acclerator Center
ian_at_slac.stanford.edu

-----Original Message-----
Sent: Tuesday, March 20, 2001 10:32 AM
To: Multiple recipients of list ORACLE-L

Ian,
This is one of those where you can get the old "it depends" answer. What type of database is this? What level of transaction activity do you have? How big are your redo logs if you switch every 15 min, 20 min, 30 min? How critical is recovery to the current time to you?

If you don't want the overhead of lots of log switches and you can stand to have a possible loss of 30 minutes of data on a recovery then 2/hr would work. (Possiblity of data loss based on losing all logs and mirror logs in a recovery scenario).

Others may have differing opinions on this, but I normally keep mine running in the 15-20 minute range. The overhead difference between 2 switches/hour and 3 or 4 per/hour is generally not noticeable. It makes for smaller archives which makes the gzip of the log run faster and take up less cpu time. (I run a cron job that compresses the archived logs to save disk space).

On Tuesday 20 March 2001 11:36, you wrote:
>
> Now for an Oracle question. It is often touted that redo logs should
> switch every 15 minutes to 30 minutes. Are these the lower and upper
> limits, should the average time to switch logs be within that range, or
> should the median be between that range?
>
> Ian MacGregor
> Stanford Linear Accelerator
> ian_at_slac.stanford.edu
>
>

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