Re: [gentoo-user] Web Server Memory Issues

[kashani]

On 1/12/2011 10:59 AM, Kaddeh wrote:
> So, I have run into an interesting problem while building out a web
> server for a client which I haven't come across before and I was hoping
> that the list would be a good way for me to find the answer.
> A little beckground on the systems:
> P4 @ 3.0Ghz
> 2GB PC2 4200
> 2x 250GB drives in RAID1
> The system configurations are default for the most part with the server
> running MySQL and Apache.
> The problem that I am running into at this point, however is that the
> machine seems to run out of memory and will segfault either apache or
> mysql when does so, when apache segfaults, it is a recoverable error,
> when mysql does it, mysql can't recover short of restarting it.
> At this point, I have found a soft fix by running a cron job every 6
> hours or so to clear the cached memory, which seems to be the problem,
> however, I would like to find a more permanent fix to this issue.
> Anything that would help at this point would be much appreciated.
> Cheers
> Kad

	Overall I'd expect your Mysql is running slow, which causes Apache to 
back up, which create more Apache children while your code blocks on the 
db, which then uses all the RAM.

1. Assuming you're running prefork, Turn KeepAlives Off if you haven't 
already. That'll reduce the number of Apache threads sitting around 
doing nothing but using your RAM.

2. The default my.conf in Gentoo (and nearly all distros) is configured 
to use 64MB. You should bump this up to 512MB total. The two settings I 
would touch are the following and THEY ARE SEPARATE POOLS that do not 
share configured memory with each other. Configure accordingly.
innodb_buffer_pool_size = 16M
key_buffer = 16M

Both variables are dynamic and can be set from with Mysql use set 
variables key_buffer='10240000'; syntax.

Assuming you use Innodb tables I'd try 256MB for that setting and 128MB 
for the key_buffer and see how it goes.

3. Mysql slow query log. Turn it on and look at it. Your db design 
sounds sketchy at best and I'd be surprised if your weren't seeing a ton 
of slow queries especially with no db tuning.

4. /tmp is how big? Make sure it's a couple of gigs so that Mysql can 
build tmp tables in it. Again your db design is strange enough that you 
might be generating large tmp tables that file /tmp (and / if you 
haven't separated them) and causes Mysql problems. This is a fairly 
common problem in my experience. The simplest solution is:
sudo mkdid -p /home/mysql
sudo chown -R mysql: /home/mysql
vi /etc/mysql/my.cnf and change to tmpdir = /home/mysql/
sudo /etc/init.d/mysql restart

Yes, tmpdir is *not* a dynamic variable so you will have to restart 
Mysql to make this change.

kashani