Monitor PostgreSQL database with munin

Install munin and dependencies.
sudo aptitude install munin munin-node munin-plugins-extra libdbd-pg-perl

Let munin make suggestions for you.
sudo munin-node-configure --suggest| grep postgres

The above should reply with several lines similar to this.

Plugin                     | Used | Suggestions                            
------                     | ---- | -----------  
postgres_bgwriter          | no   | yes                                    
postgres_cache_            | no   | yes (+ALL +gis)            
postgres_checkpoints       | no   | yes

The no | yes pattern is what we hope to see for the postgres-related plugins. That means they are installed but not enabled, and ready to be enabled. Munin makes this easy.
sudo munin-node-configure --shell
Will print a list of ln -s symbolic link commands. Select and sudo execute the symbolic link command for the plugins you wish to enable. For example, to enable a single munin-node plugin that graphs the size of all postgres databases as a stack.
sudo ln -s '/usr/share/munin/plugins/postgres_size_' '/etc/munin/plugins/postgres_size_ALL'

Repeat this for each of the plugins you wish to enable. Or, try this shortcut. If you wish to use all of the suggestions from munin.
sudo munin-node-configure --shell | sudo sh
Will execute the symbolic link commands for you.

Then wait for munin to update and you should see your new postgres graphs.