Magento Upgrade Path?

Where can I find information about upgrading Magento Enterprise 1.7. to the 开发者_如何学Pythonlatest 1.9. ?

There's no such documentation.

Your general approach:
1. Close production server
2. Backup all DBs and Magento installation
3. Turn off all your custom extensions and themes
4. Delete from HDD: core Magento modules, their layouts, all standard themes and cache.
5. Get 1.9 EE, copy it over your installation
6. Request Magento through http
7. Walk at your site, notice errors and warnings, fix them
8. Check documentation and update for your theme, whether it supports EE 1.9. Turn it on if it supports, otherwise you'll need another theme.
9. Check documentation and updates for all your custom extensions - whether they support 1.9. Turn them on - one by one.

You won't have any problem with upgrading all core DB data - it's made automatically.

You'll have problems with your custom theme, as you'll need new version with support for 1.9. And you'll need to check your custom extensions and upgrade their source and DB data to fit 1.9.

Generally all Magento upgrades work by running the updated code with the old database. The differences will be detected and incorporated automatically on the next page request. Magento keeps track of every module's version number for this reason.

Because there is a chance some modification will break it is best to do this on a new (temporary) site then add the modifications back in gradually. That way the old site is still active and uninterrupted.

I think there is no official documentation. The best way is to figure out what core functionality is used in your customizations and after that look at theirs realization in new version: does it changed or not.

To know what was changed in new version you could check changeslist