[Orca-users] Re: FW: Capacity Planning

[adrian1978b at yahoo.com]

I don't nessarly agree with this if you have priority paging turned on with < 2.8 AND the box is doing alot of file system IO. With 2.8 you don't need priority paging. We have a large 8 proc box that performs significant amounts of disk IO so there is alot of file system cache, it has a scan rate of around 300-400. With standard memory thesholds and priority paging a scan rate of < 4096 means you are only paging out file system cache(solaris internals page 184). Now a scan rate of 4096 is too high don't get me wrong but an average scan rate of 1000 or so on such a box is not far fetched. Once it reaches a 1000 consistantly I'll look into buying more ram. But when you are sholving gigabytes of data through the CPU consistantly you are going to be constantly hitting cachefree which will turn
your scan rate on no matter how much ram you put in the box.

Now with smaller boxes such as web servers, etc. I'll still side with the porsche book that a scan rate of more then 200 means problems, but with larger boxes you need to start rethinking that number.

Bob

--- In orca-discuss at y..., "Peter Viertel" <peter.viertel at i...> wrote:
> you need more RAM.
>
> A happy system never scans. In the real world you can put up with about 200 scans/s. (per Adrian Cockcroft - Red Porsche book).
>
> So first of all - audit you RAM usage, is the app leaking? or are the DBA's taking too much shared memory and not leaving enough for the kernel.
>
> If all else fails try more RAM in 2G steps until it goes away.
>
> -----Original Message-----
> From: Edwards, Mark [mailto:MarkE at p...]
> Sent: Thursday, November 09, 2000 00:38
> To: 'orca-discuss at egroups.com'
> Subject: [orca-discuss] FW: Capacity Planning
>
>
>
> > Hi,
> >
> > I have been asked to produce a capaity plan for one of the platforms that
> > our company runs, however the platform appears to be RAM bound at the
> > moment. (Page Scan rates high and residency times low at times of peak
> > demand). I am also noticing an potential issue with CPU usage. These
> > servers have 6 CPU's on board and 5Gb RAM, however looking at the
> > description you have given of the 'CPU usage' graph - particuarly where
> > you say:
> >
> > "If idle time is always low, check the number of processes in the run
> > queue. More, or faster, CPUs may be necessary. If user CPU time is
> > commonly less than system CPU there may be problems with the system set
> > up."
> >
> > I am noticing a consistent difference between the user and system CPU
> > usage where the user CPU usage indeed appears to be less than the system
> > CPU usage. Might this be additional evidence of a RAM bound state - high
> > amounts of VM swappage going on?
> >
> >  <<o___usr_pct,__sys_pct,__100_-_usr_pct_-_sys_pct-weekly.png>> 
> > <<o___scanrate-daily.png>>  <<o___page_rstim-daily.png>>
> >
> > Please forgive me for asking this of you, but I am a tad new to capacity
> > planning and graph interpretation, and looking for some assistance...
> >
> > Mark
> >
> > Mark P. Edwards
> > Pacific Access IT
> > MarkE at p...
> > +61 3 9281 3522
> > +61 407 322 033
> >