Re: How Many CPUS??

From: koert54 <nospam_at_nospam.com>
Date: Fri, 16 May 2003 14:39:57 GMT
Message-ID: <1L6xa.4751$1u5.397@afrodite.telenet-ops.be>

you need to check your runqueue

if your runqueue is consistently higher than the number of CPU's you'll benifit from extra CPU's
if your runqueue is consistently lower than the number of CPU's -> adding CPU will not make things go faster, you could even do with less

how to get the runqueue
1. uptime - gives you the load which is on most unix flavours the 1min, 5min, 15min average of your runqueue
2. top, topas, nmon whatever, will give you the runqueue 3. sar : this is the most interesting way - log on as adm
- check the crontab - most unix flavours have already an example setup in which
they use sa1 and sa2 gather stats and report on them. Increase the default frequency from 20min
to 5min for *real* stats

- check /var/adm/sarXX for daily reports
- look for runqueue size & runqueue occ%
- load the columns rq sze & rq occ% in excel
- runqueue stats = rq sze * occ%/100  ->>>>> make a graph and voila you've

plotted a wicked graph of your runqueue

ATTN - check your unix flavour for the exact meaning of runqueue as this can differ from
platform to platform. On Tru64 it's completely different than on AIX/Solaris/HPUX

One can say that if your runqueue is higher than 2 to 3 times the number of CPU's, there's
severe CPU starvation and things will come to creeping halt - typically you'll have 99%usr time
1%sys, 0%idle 0%wio. Typically - you'll see this is on boxes with DBA's using PQ !!! :-)
While I'm at it - don't use parallel degree 'default' at table level in combination with CBO and
the default max_parallel_servers=5 - it'll kill your performance. Use a degree of one (alter table x noparallel) or set max_parallel_server=0 if you're not doing warehousing or if you don't have a big smp box

This is what I do and use as rule of thumb - if someone else has a better sugestion it's much
appreciated.
Might I sugest reading optimizing unix for performance (old but good book) which clearly explains
runqueue, waitqueues etc
http://www.amazon.co.uk/exec/obidos/ASIN/0131115510/qid%3D988550994/026-0642 492-7664436

regards !

"Rahul" <rahul_ocp8i_at_hotmail.com> wrote in message news:f8af2f95.0305150601.2acd169d_at_posting.google.com...
> Hi everybody,
>
> One simple question. Lets say, if i have 8 cpus on my server, how can
> i check if i am utilizing all the cpus and how will i benefit if I add
> more cpus on the server.
>
>
> Thanks.
Received on Fri May 16 2003 - 09:39:57 CDT