Server Update, Too Many Apache Processes But Low Load

I have 2 almost similar webservers:

debian 3.2, P4 3GHZ, 1 Gb ram, kernel 2.6, apache2, php4

Initial apache2.conf:

Code:
Timeout 4
KeepAlive Off
KeepAliveTimeout 2
ServerLimit 1500

<IfModule prefork.c>
StartServers 10
MinSpareServers 10
MaxSpareServers 15
MaxClients 1500
MaxRequestsPerChild 3000
</IfModule>

I update the sources.list on server 1 to mirrors of the new debian 4 etc . I run apt-get update and apt-get dist-upgrade . A whole bunch of things get updated (it was long time ago that I did this anyway). After some troubles with /boot/grub/menu.lst the server boots ok, and everything is well. This server used to have loads of 15-25 at peak times, but after the update its running very smooth with loads of 2-3 at the same peak times. I dont know why exactly, as I noticed updates in OS , kernel version (from 2.6.8x to 2.6.18) , apache2 , php (4.4.4-8+etch1) , and I also needed to update eaccelerator from 0.94 to 0.95 .

A few days later I update server 2. Everything seems to go the same, although the kernel version stays at 2.6.8-3-686. I dont think kernel version at start was exactly same at server 1. But the new php version is the same as server 1, and everything else looks the same too.

But when peak times are coming up, this server starts to have troubles. It is quickly rising to total of 200-300 processes , while server 1 always stays stable at 60-70.

Server 2 also reacts slow if I click somewhere on the site. It takes 5-10 seconds to show a new page. However the load stays pretty low at 1-2 . I see no big cpu usage and also no big memory usage. I have the impression that this server 2 is somehow wasting a lot of apache processes and is making things hard for itself without a real reason.

When I check the seperate mysql database server, I also notice a lot of processes.

Around 200-250 whereas it used to be 40-60. Sometimes this adds up so hard, that all webservers are blocked because mysql has too much processes. When I check the mysql connections, I see a few dozen things like 'unauthen ip:port Connect login' just hanging. All of them have the ip of webserver 2. Those extra apache processes are somehow hanging on to the mysql server without really doing something.

I dont know what is happening, but this server is underperforming very badly now. I managed to limit the problem by drastically lowering ServerLimit and MaxClients on webserver 2 , but this is no real solution. The server is still slow, at least now its not bringing down the others.

My question : what should I check for now ? I noticed a different structure in the conf files in debian etch, maybe something new has a bad influence on my old conf files? Is there something wrong with the combination of kernel+php version? I have no idea, please point me in the right direction so I can learn from this.