april 15, 2009 : steve kong : 2 comment(s)
I was archiving off my 2008 email last night (I know, running a bit late). I figured that it would be a lot faster doing it via Squirrelmail for some reason -- most likely just my tired brain making irrationale decisions.
I started to archive and it was running fine, then it got slower. Then it got a lot slower. Then it came to a grinding halt, when I looked on my VPS, I saw that my swap space was all used up and I had exhausted all the memory (360MB is quite limiting, now I know).
So, what did I discover?
- Squirrelmail, because it can't keep a state, opens one IMAP authentication session per thing you do. Since I was doing lots of stuff at once, it kept opening authentication sessions with dovecot. Dovecot, set to take lots of sessions kept opening them up at 5MB a pop.
- SpamAssassin + mysql backend for Bayes is quite heavy. When a cron'd task to learn spam from users' folders kicked off at the same time I was sorting through mail, this sucked up lots of RAM.
- Apache is setup for gobbling RAM. Lots of modules loaded and lots of children fired up by default.
I ended up having to reboot the VPS and start tweaking for lower memory requirements. I lowered the number of children that Apache starts up with and also the max number that it can have running. I turned on Apache's keep-alive function and change the time-out period to two seconds. I also went through and disabled a bunch of modules (webdav? Not using it, don't need it. Etc.)
SpamAssassin is running as a daemon, so I cut down the number of children for SpamAssassin from five to one (in CentOS edit /etc/sysconfig/spamassassin). I set the max-spare to one also. Checks coming from exim are queued for SpamAssassin if things get busy -- but, using zen.spamhaus.org in exim as an RBL to deny known spammers helps cut down the need for SpamAssassin to scan mail.
I tweaked some settings in /etc/my.cnf to lessen memory usage.
And, for dovecot, I setup caching for logins. I set the login_processes_count to two and login_max_processes_count to six since this is only a small mail server. I also set login_process_per_connection to "no". This makes things a tidbit less secure, but allows dovecot to not create processes for each login.
I guess I could work on switching to lighttpd and move away from apache. We will see about that.
Comments
Get rid of apache altogether. It's an absolute memory hog, and for most setups, overkill. Try Cherokee instead - its lightweight and damn fast (and a damn side easier to configure and maintain than Lighttpd).
@rowlc
April 15, 2009 @ 01:21 PM
I moved from apache to lighty a couple months ago, and I did indeed see an appreciable increase in performance and drop in memory use. However, Lighty's mod_rewrite isn't as capable as Apache's, so I've found that I've had to drop niceties like clean urls for my web apps. My big problem is that Lighty's reverse proxy support can't map e.g. server1/foo to server2/bar the way Apache can. I'm starting to look at nginx, because its rewriting and reverse proxying looks to be a bit more advanced than Lighty's.
pratfall
April 15, 2009 @ 02:24 PM