db_migratecatalog 
Use this command to migrate the database catalog.
Afterwards the database catalog uses the Unicode character set instead of the ASCII character set. This command does not affect the format of the user data in the database.
User passwords may have no more than 18 characters in ASCII databases and no more than 9 characters in Unicode databases. After the migration, all users can still use their existing passwords to log on, but only the first 9 characters are evaluated.
The duration of the migration depends on different factors, like hardware, database size, and so on. You can use the following information as an indication:
Duration of a catalog migration for the database of an R/3 system containing approx. 7,000 tables, on an Intel® Pentium® 3 computer with a 700 MHz processor: approx. 10 min.
Duration of a catalog migration for the database of an R/3 system containing approx. 33,000 tables and approx. 5,700 views, on an HP computer (no additional information given): approx. 40 min.
Recommendation
To take precautions against an error during the migration process, carry out a complete data backup in the ADMIN operational state before migrating the database catalog.
Carry out another complete data backup after successful migration. This is the only way to ensure that you can restore the database with the migrated catalog data in case of a database error later on. It is also a prerequisite for switching on the automatic log backup function.
Prerequisites
The database is in the OFFLINE operational state.
You have the server permission AccessUtility.
Structure
db_migratecatalog
Result
The catalog data of the database has been converted into the Unicode format. The database is in the ONLINE operational state.