Re: Perf Issue - Wait IO is High
From: Bill (bverzal_at_komatsuna.com)
Date: 02/04/04
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Date: 4 Feb 2004 06:31:49 -0800
robogrande@yahoo.com (robogrande) wrote in message news:<e6f7eb76.0402031048.288115b0@posting.google.com>...
> Looking for opinions on this performance issue, sorry it is a long
> one:
>
> BACKGROUND: I have an AIX 5.1 Regatta LPAR with 4 processors and 16
> GB of memory. We run Oracle 8.1.7, the database just less than 1 TB
> in size, on an HDS SAN, which is performing well. The database is
> for OLAP (essentially batch) applications.
>
> THE PROBLEM: Too many processes are on the wait queue (Typical stats:
> Runqueue= 1, Waitqueue=5, WIO at 40%).
>
> OTHER DETAILS: no physical paging, but high page-in rates. Free
> memory pages stays down around the low threshhold of 120 pages, scan
> rate typically 7000 with free rate about half that. Vmtune setings
> are at the defaults, and NUMPERM stays right about at the default 80%
> threshhold. Number of AIO servers are 20,40... seems OK but I am
> going to increase those numbers just to be safe.
>
> MY THOUGHTS: 16GB is a lot of memory, but it looks to me as if the
> application has an insatiable demand for file pages (most likely
> Oracle datafile pages), and it is constantly reading new ones in.
> Because it is such a large database, I am not sure I can satisfy those
> demands short of buying a truckload of memory. Most tuning
> recommendations that I read for Oracle are to reduce the Perm (file)
> memory pages with vmtune, but since that is what the app needs most
> that makes no sense to me here. Thinking of increasing maxpgahead...
>
> TIA...
Traditionally, Oracle recommends setting minperm to 5 and maxperm to
10. If you say that the vmtune settings are default, then these
values are probably 20/80.
I suggest you change the minperm and maxperm. This will keep the FS
cache from taking all the memory. As well, you should set
hard-limit=1. This will make the settings a hard limit and nest
utilize the settings.
BV
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