That said, my experience is that the more posts you have the more likely you will get timeouts and issues using the web interface. Keep the CLI method in your back pocket and if you have 100,000 or more posts I would use CLI first.
In spite of attempts to make it bulletproof, I also often find that other database issues have to be fixed during an upgrade. For example, I often have to create the
phpbb_config_text table manually. Don't be surprised if you get an error or two during any upgrade. You will just have to puzzle through it and make some correction, usually in phpMyAdmin or similar tool, to successfully upgrade. In addition, some steps seem like they will take forever, sometimes hours on larger boards. Just hang in there. They usually involve reformatting the