I doubt this is a MySQL problem. We are using MySQL in several environments, including vpopmail. My guess is I don't have as many users as you, since I set my pop3 concurency at 30 with no problems.
Are you running qmail-scanner or spamassassin? These added quite a bit of load to my mail server (dual 2.8 Xeons, 2GB RAM) but it still averages at around 0.3 for the 5min average. It will spike if Razor is slow to respond or one of our customers does a blast e-mail to thier client base.
You can try and put MySQL on a seperate server and just have vpopmail connect to the external database and see if that solves any load problems.
BTW, What versions are you running?
I cannot add more RAM to the server.. :(
I am running qmail-scanner 1.21, spamassassin 2.63(spamd), clamav 0.70, File::Scan 1.15, also I have patched tcpserver to deny connections if the load average is greater than 12 or more than 5 connections from the same IP address. This alleviated the problem temporarily.
I have gathered the following average daily stats: 438 IMAP connections 0 Rejects due to load/maxip 28708 POP3 connections 308 Rejects due to load/maxip 7355 SMTP connections 128 Rejects due to load/maxip
Bloquing: 10 Emails due to policy reasons 2923 Emails due to Virus 595 Emails due to Spam > 15.0 pts.
39.4% spam/ham ratio
Each instance of mysql Ver 11.18 Distrib 3.23.58, for pc-linux (i686) uses
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME COMMAND 1055 mysql 9 0 14500 9376 1152 S 0.0 1.8 4:28 mysqld
So when there are several concurrent POP3 connections, another instance of mysql is spawned to query the DB. I think this is whats bringing the server to its knees...
In any case, has anyone done a MySQL to CDB migration?
Intercom El Salvador