Re: DBWR - How Many is Too Many?
- From: Nuno Souto <dbvision@xxxxxxxxxxxx>
- Date: Fri, 29 Feb 2008 00:38:04 +1100
David Barbour wrote,on my timestamp of 28/02/2008 5:53 AM:
We recently moved our database to a new SAN. Performance has just
tanked. Here's the environment:
AIX5.3L
Oracle 9.2.0.7 <http://9.2.0.7>
SAN - IBM DS4800
Aye...
sar is scary (just a small portion)
AIX r3prdci1 3 5 00CE0B8A4C00 02/27/08
System configuration: lcpu=8
00:00:00 %usr %sys %wio %idle physc
02:15:01 19 19 42 19 4.00
02:20:00 21 25 40 14 4.00
02:25:00 19 18 43 20 4.00
02:30:00 18 18 43 21 4.00
02:35:00 20 24 40 16 4.00
wio is w-a-a-a-a-a-y too high with sys time low,
might well be a I/O misconfiguration.
1. One db writer for each database disk - in our case that would be 8
2. CPUs/8 adjusted for multiples of CPU groups - in our case that would
be 4
Any thoughts?
Large datablock waits in db, plus lots of wio
in the OS.
I'm thinking possible misconfiguration
of the AIX Disk I/O pacing parameters.
From memory, it's:
smitty chgsys
and check all file systems for minpout and maxpout
values. Unless you know in detail the I/O balance
of your system, you're much better off with these
two set at 0 (zero).
There are papers at IBM on this subject, gogle
for "IBM AIX disk I/O Pacing".
Had a similar situation a while ago: a new SAN's
file systems for some reason ended up with 30/30
for both pout pars. When we set them to 0, the
wio dropped very significantly.
At least worth checking.
--
Cheers
Nuno Souto
in rainy Sydney, Australia
dbvision@xxxxxxxxxxxx
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