Conversion of an application database to minimize time in single-user access mode

A method and system for converting source tables of a database of the application to target tables of a new version of the database while reducing the amount of time that the database needs to be open in single-user access mode is provided. A conversion system divides the conversion into a multi-user phase and a single-user phase. During the multi-user phase, the conversion system can perform most of the conversions while the database is opened in multi-user access mode. The conversion system stores the converted data in auxiliary tables, rather than updating the source tables. During the single-user phase, the conversion system performs the remaining conversions and copies data from the source tables and the converted data from the auxiliary tables to the target tables.