Re: LGWR using lots of CPU time, low CPU usage

At 10:50 AM 11/26/2002 -0800, you wrote:
>Second, if what you are telling ("logs are about 100 MB in 2 groups of 20
>members each") is accurate, then this is your main problem. If you have
>your log switches on avg 2.5 per day, change your RedoLog configuration <snip>
>You will have more log switches
>per day, but it's perfectly fine as long, as don't have them every 5 min.

Oracle tells me to set redo logs according to the busiest period of log switching, even if they happen once a week. At least 20 times in the last month I had log switches with 1-3 minutes between switches. Accordingly to Oracle, I should increase their size again!

>And "old school" is still right about not putting RedoLogs onto RAID5.

 From what I'm being told, this is not your father's RAID5. This is what they tell me:

The CPU hands the IO to the disk controller and rather than do the physical disk IO while the process waits, the disk controller caches it to local memory and says done. Therefore, effectively there is no wait for IO and it doesn't matter if we are RAID 5 or RAID 0+1, the system is NOT waiting for the IO. He said the only time there might be a delay is during the cache's battery refresh times. I checked your dates and it was not occurring during those times. Also, if you look at the iostat statistics under the 'wait' and '%w' headers you will see all zeros.

I did run iostat while this logwriter process was clunking away and they were all zeros. I have a bottleneck, but there is no indication it is in disk.

Debi

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Author: Deborah Lorraine
  INET: debil_at_ucdavis.edu

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