Act performance hints

The following describes steps you can take to get the best performance out of your Act installation, in a production environment. Full explanations of the techniques used are outside of the scope of this document, so we only provide introductory comments.

pre-loading modules at Apache startup and persistent database connections

Insert the following configuration directive in httpd.conf:

PerlModule $ACTHOME/conf/startup.pl

This improves performance (modules are pre-loaded at server startup) and memory usage (modules are loaded in the parent server and thanks to copy-on-write their code is shared, at least for a while.)

startup.pl also uses Apache::DBI to enable persistent database connections, obviating the need to connect to the database for each request.

Dual Apache setup

mod_perl-enabled servers tend to have a large memory footprint, so you don't want too many of them. Server instances tend to spend most of their time serving responses to slow clients ("spoon-feeding" clients.)

This setup uses 2 instances of Apache: the front-end, or "light" server serves static content (images, CSS files), and reverse-proxies dynamic content to the back-end, or "heavy" server.

The light server uses mod_proxy but no mod_perl, therefore its memory footprint is much lower. The heavy server sends its output to the light server very fast, so it isn't tied up spoon-feeding the clients. With such a setup it is possible to serve a high request rate with relatively few back-end processes.

In the example below we choose to run both instances on the same machine. The heavy server runs on localhost on a high port, while the light server runs on our public IP on port 80. This also provides protection against direct access to the heavy server.

Here's the relevant configuration snippet for the heavy server:

  BindAddress     127.0.0.1
  KeepAlive       Off

You want to keep KeepAlive Off so as not to keep server processes tied up doing nothing.

  MinSpareServers     5
  MaxSpareServers     5
  StartServers        10
  MaxClients          20
  MaxRequestsPerChild 500

These numbers are only an indication, tailor them to your requirements and amount of available RAM. We keep MaxClients low because that's the whole point of this setup, and MaxRequestsPerChild low to improve sharing.

  PerlRequire /home/act/conf/startup.pl
  Listen 9000
  <VirtualHost 127.0.0.1:9000>
    ServerName    www.example.com
    DocumentRoot  /home/act/wwwdocs
    Port          80
    Include       /home/act/conf/httpd.conf
  </VirtualHost>

In this context, the Listen directive specifies which port this server listens to, and the Port directive specifies which port to use when issuing a redirect.

In the light server, enable mod_proxy and mod_rewrite. We'll use them to reverse-proxy requests for dynamic content to the back-end. Again, adjust the numbers to your requirements and hardware.

  MinSpareServers 10
  MaxSpareServers 15
  StartServers    100
  MaxClients      200

  <VirtualHost *:80>
    ServerName    www.example.com
    DocumentRoot  /home/act/wwwdocs

    RewriteEngine       on
    RewriteOptions      'inherit'
    RewriteRule         \.(css|gif|ico|jpg|pdf|png|txt)$    -                        [L]
    RewriteRule         ^/(.*)$                             http://127.0.0.1:8000/$1 [P,L]
    ProxyPassReverse    /  http://www.example.com/
  </VirtualHost>