I would like to upgrade a PostgreSQL 8.3 server to PostrgreSQL 8.4. There are many software components that interact with the server over the network, and I am concerned with compatibility issues.
Is there any interface change between the different versions of PostgreSQL, as far as an external component is concerned?
Unfortunately, without knowing your system (inside and out), it's going to be difficult for anyone to tell you how an upgrade is going to impact you.
I'd recommend checking the release notes to verify that the upgrade path won't mess up the application.
Here are a couple changes that I noticed that you might need to know about:
Remove ipcclean utility command
Changes in the TRUNCATE and LOCK statements
SELECT DISTINCT and UNION/INTERSECT/EXCEPT no longer always produce sorted output
Disallow LOCK TABLE outside a transaction block
Remove support for the (insecure) crypt authentication method
Modify the ALTER TABLE syntax to allow all reasonable combinations for tables, indexes, sequences, and views
I'd recommend trying this on a test machine first (if possible).
I don't know of any changes that break backwards-compatibility - see here for some general upgrade hints as you can't use pg_upgrade
You will of course want to test the upgrade away from your production environment first
You should carefully(!) read the changes from 8.4 to 8.3. See if anything relates to your setup and fix it accordingly.
