The best method for update to IPS 4 if you have a large sql database

[Marius]

How to proceed when the forum has a large sql database? 

I tried to update the site on a test subdomain and during the upgrade required running the conversion of database via the Command Line.  

What to do to avoid a long period in which site to be offline?

Thank you.

[Vroom]

If the database is large I would do the upgrade on a backup database that isn't being accessed by visitors, and then switch it in after the upgrade is completed.