[WBEL-users] Re: [CentOS] real used RAM!

[Nick Bright]

On 5/30/05, Bryan J. Smith <b.j.smith at ieee.org> wrote:
> On Mon, 2005-05-30 at 10:10 -0500, israel.garcia at cimex.com.cu wrote:
> > List, I've installed my CentOS Server running progress 9.1D database
> > system, with only 15 users working every day, this server has 2GB RAM,
> > so, my question is:
> > Why the 2GB of RAM is always used? Even with only one user connected...
> > How can I messuare the real RAM MEM used by my system split in proccess?
> > Is there another tools which I use to compare the results from top. Or
> > vmstat?
> 
> There is vmstat, iostat, etc... all sorts of things for tracking memory,
> I/O and other usage.
> 
> The Linux kernel is very dynamic when it comes to how it manages user,
> buffer and cache.  It's a very efficient approach that works well.  In
> dealing with databases, you're going to have very large reads/commits
> that will be cached/buffered, as well as the binaries involved (which
> can be very extensive).  So the kernel will typically be using all of
> your memory at any time, although it will drop cached as soon as it
> needs it for user or buffers.
> 
> BTW, on anything but an AMD64 platform, 2GB can be a "weak spot" in
> memory size.  You typically either want to be 1GB (actually, 960MB), or
> 4GB+, because of the performance hit that occurs when you use the 4/4GB
> model versus the 1/3GB model for anything but AMD64 (even Intel EM64T
> has some issues with its 32-bit AGTL+ physical platform).

I'm curious for more information regarding this topic. I'm getting
ready to deploy a new server (WBEL3 of coruse) with postfix, cyrus,
and LDAP for a non-trivial installation (25,000 to 35,000 mailboxes).
I've got 2Gb of physical memory, because I know that 1Gb will not be
enough for everything the machine has to do.

If it's really that big of a deal, I can force the issue with
management and get myself 4Gb of memory for the box. But before
spending that kind of money, I'd really need to know what exactly the
differences are :)

My platform is a dual Xeon (HT enabled) system, I'm not sure on the
chipset E71xx I think? Anyways, If you could I would appreciate more
details on this subject.

> 
> Just something to be wary of.  It will depend on your application if
> 2GB is better than 1GB on a 32-bit physical Intel/AMD platform, instead
> of AMD64 (which is a 40-bit physical platform).
> 
> 
> --
> Bryan J. Smith                   mailto:b.j.smith at ieee.org
> ----------------------------------------------------------
> Beware of those who define their preferences in terms of
> hate of another option, than on the merits of their choice
> 
> 
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