Retain content IDs
At this point, you will also be asked if you want to Retain content IDs. This option can only be used on a completely empty XenForo installation, that has no threads and posts. The setting will attempt to retain the IDs of the data that is imported, so that a thread that has an ID of 2563 in the source database will be imported with an ID of 2653 in the XenForo database.
