I really would prefer to have my own server but sticking a box in colo is expensive. Where I live, getting access to the physical colo space would be nearly impossible too. As a result I run on a VPS. Unfortunately VPS has some horrible limitations depending on who is on the box with you.
Recently I decided to move my personal blog off of b2evolution and stick it on Drupal. Too bad drupal is such a resource hog. Most CMS and blog software is though and it is really hard to find a minimalized, optimized blog software that uses any form of caching. Today, it hit the skids and my patience hit the wall. Argh!
I was converting my personal blog by hand because I only have about 30 entries so it didn’t pay to write a conversion script. Everytime I hit the ‘post’ button in Drupal I wound up with a blank screen, could not connect or worse, the results of any command in SSH terminal window showed a “could not allocate memory”. As a result, I had to do some fast tuning of something because I had to reboot the server after every blog post!
I chose to tackle Apache first because they have an Apache Performance Tuning Guide that helps a bunch. Postgres, well I’m running an old version that I really need to upgrade before I tackle configuration and optimization of it. That’s not a 30 minute job.
VPS, Apache and Low Memory
VPS has a low memory for sure. Even though you can sometimes burst more, in general it is pretty low. The very first thing in the Apache performance tuning guide is tackling memory.
You can, and should, control the MaxClients setting so that your server does not spawn so many children it starts swapping. This procedure for doing this is simple: determine the size of your average Apache process, by looking at your process list via a tool such as top, and divide this into your total available memory, leaving some room for other processes.
Using top and sorting by thread using ‘h’ I am able to see that the average Apache processes is using WAY TOO MUCH memory at 25M a piece – and 10 processes running. I don’t have time to tune the size now so I’ll tune the number of servers using very simple configuration parameters. Since we are using MPM Prefork, the directives can be found in extra/httpd-mpm.conf file under mpm_prefork_module.
Since I am supposed to be guaranteed 256M memory burstable to 1G I’ll optimize to the lower number. 256M / 25M is 10. Not including room for other processes. The current setting is 150!
I also changed it to only start 2 servers, only keep 2 spare servers instead of 5, and only allow 10 clients instead of 150. This will essentially create a queue if anyone is waiting but it shouldn’t dip into swap space and it will save a bunch of memory usage. This will of course be monitored. Once time permits and I am able to minimize the size of each Apache2 process (the other factor) then I will revisit this and likely increase the MaxClients accordingly.