You best be careful, Jared. You KNOW how uptight and evil Tim can be! :)
-----Original Message-----
Sent: Wednesday, November 27, 2002 9:56 AM
To: Multiple recipients of list ORACLE-L
Oh boy, is my face red!
I remembered that of course, as soon as I saw this.
I need to keep better track of who I'm plagierizing. :)
Jared
"Cary Millsap" <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
11/26/2002 03:05 PM
Please respond to ORACLE-L
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
cc:
Subject: RE: LGWR using lots of CPU time, low CPU usage
The ultimate sincerest form of flattery is for someone to attribute
something smart to you that you wish you had done but, alas, did not
actually do.
(It was Tim Gorman who posted the excellent analogy.)
Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
Upcoming events:
- Hotsos Clinic, Dec 9-11 Honolulu
- Hotsos Clinic 101, Jan 7-9 Knoxville
- Steve Adams's Miracle Master Class, Jan 13-15 Copenhagen
- 2003 Hotsos Symposium, Feb 9-12 Dallas
-----Original Message-----
[EMAIL PROTECTED]
Sent: Tuesday, November 26, 2002 4:07 PM
To: Multiple recipients of list ORACLE-L
> >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.
Debi,
That is true, up to a point.
Think of the cache as a water tank. You have a garden hose
filling up the tank. You can keep increasing the water
pressure for a while.
But the outlet at the other end of the tank has a fixed
capacity. It flows 10 GPM, and no more.
What happens when you increase the flow at the intake to
20 GPM?
The tank fills up.
When the tank fills up, your intake flow will need to decrease,
because you can only flow 10 GPM at the outlet.
Now, think of the outlet as writing to disk, the RAID5 cache
is the water tank, and your database is the inlet that wants
to run at 20 GPM.
If your database activity will never be intensive enough to
stress the cache like this, no problem. But 'never' is a
very long time.
If any of this sound familiar, Cary Millsap posted a very similar
explanation a few weeks ago.
Plagierism is the sincerest form of flattery. :)
Jared
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