CentOS - Feb 2007 - CentOS 3 vs. CentOS 4 Memory Utilization

I'm helping some folks who have a CentOS 3 i386 server with 512MB of
RAM.  The output of 'free' looks like:

$ free
             total       used       free     shared    buffers     cached
Mem:        511428     497956      13472          0      29868     178280
-/+ buffers/cache:     289808     221620
Swap:      2040244     120644    1919600

The box does not even have X installed... it's basically a web
application and email server.  They would like to upgrade to CentOS 4,
but are concerned that it could be considerably more "memory hungry"
and lead to memory starvation (they don't want to add more RAM to the
box at this time, although that could be an option down the road).

I ran some tests under VMWare with fresh installations of CentOS 3 and
CentOS 4 (both using a "minimal install", the same as the server in
question) and CentOS 4 seemed to only use 10-25MB more memory.
However, it's hard to know how this will translate into real-world
performance over time and with the application installed.

Does anyone have any experience that would suggest how much more
memory a non-X server like this might require?  If the application(s)
on the server stay the same, do you think we would run into issues
where memory would be depleted to a level that would cause concern?

Many thanks,
KC

On Thu, 2007-02-08 at 22:33 -0500, hkclark at gmail.com
wrote:
> I'm helping some folks who have a CentOS 3 i386 server with 512MB of
> RAM.  The output of 'free' looks like:
> 
> $ free
>              total       used       free     shared    buffers     cached
> Mem:        511428     497956      13472          0      29868     178280
> -/+ buffers/cache:     289808     221620
> Swap:      2040244     120644    1919600
> 
> The box does not even have X installed... it's basically a web
> application and email server.  They would like to upgrade to CentOS 4,
> but are concerned that it could be considerably more "memory
hungry"
> and lead to memory starvation (they don't want to add more RAM to the
> box at this time, although that could be an option down the road).
> 
> I ran some tests under VMWare with fresh installations of CentOS 3 and
> CentOS 4 (both using a "minimal install", the same as the server
in
> question) and CentOS 4 seemed to only use 10-25MB more memory.
> However, it's hard to know how this will translate into real-world
> performance over time and with the application installed.
> 
> Does anyone have any experience that would suggest how much more
> memory a non-X server like this might require?  If the application(s)
> on the server stay the same, do you think we would run into issues
> where memory would be depleted to a level that would cause concern?
> 
It should not be a problem as lots of your memory used is buffers and
cache.

CentOS-3 is going to be supported for a while yet (EOL is scheduled for
Oct 31, 2010), so if it is working perfectly and doing what they want,
they may want to keep it though.

If they upgrade or don't, the memory should be OK either way .
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On Thu, 2007-02-08 at 22:33 -0500, hkclark at gmail.com
wrote:
> I'm helping some folks who have a CentOS 3 i386 server with 512MB of
> RAM.  The output of 'free' looks like:
> 
> $ free
>              total       used       free     shared    buffers     cached
> Mem:        511428     497956      13472          0      29868     178280
> -/+ buffers/cache:     289808     221620
> Swap:      2040244     120644    1919600
> 
> The box does not even have X installed... it's basically a web
> application and email server.  They would like to upgrade to CentOS 4,
> but are concerned that it could be considerably more "memory
hungry"
> and lead to memory starvation (they don't want to add more RAM to the
> box at this time, although that could be an option down the road).
> 
> I ran some tests under VMWare with fresh installations of CentOS 3 and
> CentOS 4 (both using a "minimal install", the same as the server
in
> question) and CentOS 4 seemed to only use 10-25MB more memory.
> However, it's hard to know how this will translate into real-world
> performance over time and with the application installed.
> 
> Does anyone have any experience that would suggest how much more
> memory a non-X server like this might require?  If the application(s)
> on the server stay the same, do you think we would run into issues
> where memory would be depleted to a level that would cause concern?
---
I wouldn't think so, this system actually does have some x-stuff
installed.

# cat /etc/redhat-release
CentOS release 4.4 (Final)

# free
             total       used       free     shared    buffers
cached
Mem:        515604     509760       5844          0      37832
117296
-/+ buffers/cache:     354632     160972
Swap:      1048568     268324     780244

It's running
httpd/php5/mysql-4/postfix/amavisd-new/ejabberd/ntp/cupsd/apcupsd
(slave)

Craig

On 2/8/07, Johnny Hughes <mailing-lists at hughesjr.com>
wrote:
>
> It should not be a problem as lots of your memory used is buffers and
> cache.
>
> CentOS-3 is going to be supported for a while yet (EOL is scheduled for
> Oct 31, 2010), so if it is working perfectly and doing what they want,
> they may want to keep it though.
>
> If they upgrade or don't, the memory should be OK either way .
>
Hi Johnny,

Good info -- thanks.  They have a small app they want to add that
requires a newer version of Perl than 5.8.0 that comes with CentOS 3.
Rather than getting into a non-RPM version of Perl, we were thinking
going to CentOS 4 would be easier and cleaner.

In your experience, would you say that my "quick & dirty"
measurement
of CentOS 4 needing 10-25 MB more memory than CentOS 3 (again, for a
non-X box with a minimal install) is accurate (at least in approximate
terms)?  Or is there something I'm not taking into account -- e.g,
some of the libraries and/or other "basic server apps" such as apache
with PHP or MySQL will make that number much higher?  Although this
box is doing OK on memory now, I would hate to kill their possible
expansion plans just because we did an upgrade and it sucked up way
more memory than we though.

Again, thanks for all the great things you and the CentOS team are doing!

Regards,
KC