I'm using Debian 6 (Squeeze) in production for a couple of websites. I decided to use postgresql backports so that I could use PostgreSQL 9.0 features. I thought that it would remain 9.0 and receive updates to that major version.

Unfortunetly Squueze backports were updated to PostgreSQL 9.1 so probably I won't receive updates to 9.0.

I'm planning upgrading to 9.1 but I know that it's not done automatically.

I've read about official pg_upgrade and debian's pg_upgradecluster, but I would appreciate complete guide to upgrade.

1. What are steps to do (first apt-get install postgresql, then pg_upgradecluster, then remove old cluster)? List of steps would be nice.
2. What are possible failure scenarios?
3. How to prepare to failures and react on them?

I can stop database for a couple of hours only so I want to be prepared