Is it possible to successfully migrate from Odoo 8 to Odoo 9 through Openupgrade migration scripts given in https://github.com/OCA/OpenUpgrade.

We have been trying to upgrade a Odoo 8 instance (which is customized for client requirements) to Odoo 9 using that which is running almost a week now.  It is looping in exchange rate loop for account move lines.  Can anyone please  help me in assisting this ?  Am I missing anything ?

fyi - There are 800k account move lines in the Database I am trying to upgrade