Re: IO waits in SAP/Oracle

I think that this is simple:

1. If you have idle cpu and you do I/Os, the wait time (or idle time) for the I/O is counted as waiting for I/O.
2. So having WIO is not a bad thing, it means that you have plenty of CPU to spare.
3. buffer cache hitratios are useless. In your case you should ask your self the question if you are happy with the overall performance of your systems (from an response time point of view). What counts is the speed of the I/O.
4. What you can do is to upload an report.txt file (from bstat/estat) with timed_statistics = true to this site http://www.oraperf.com. It will show you the overall response time and wait time for your system.

Anjo.

thuge wrote:

> Hello,
>
> I have a "philosophical" problem about my SAP/Oracle/AIX database :
> I'm quite sure i have some IO waits problem :
> - sar + vmstat give me about 50% of the time is spent in IO wait
> - iostat : mainly the most accessed disks are those which contains the
> Oracle data files.
> - Precise/SQL, SQL tuning tool, tells me that 95% of the SQL statements
> spent their time in IO wait
>
> BUT the Oracle Buffer Cache Hit Ratio is always between 95% and 98%,
> that is to say Oracle finds more than 95% of the data in its buffer then
> there's no disk access. Am i wrong ?
>
> The system is only for SAP/Oracle, the paging is low.
> Could someone explain this ???
> Could these IO waits come from another thing than SAP/Oracle ?
>
> Thanks for your help,
>
> --
> Thierry HUGE
> AIX/Oracle/SAP Administrator
> STEELCASE STRAFOR (FRANCE)
>
> Sent via Deja.com http://www.deja.com/
> Share what you know. Learn what you don't.
Received on Fri Jul 09 1999 - 08:43:40 CDT