On-demand database catalog upgrade

A method comprising:

• performing a selective upgrade of a database instance from a first version of a database to a second version of the database, wherein the selective upgrade causes the database instance to refer to the second version of the database, and the selective upgrade does not modify, in the database instance, a reference to a first system catalog table and a second catalog table of the first version;
• receiving a first request from an application to access the first system catalog table and a second request from another application to access the second system catalog table;
• identifying a first set of rows in the first system catalog table by searching every row of the first system catalog table, the first set of rows matching requirements of the first request;
• identifying a second set of rows in the second system catalog table by searching every row of the second system catalog table, the second set of rows matching requirements of the second request;
• and
• modifying, while the database instance referring to the second version of the database is running, the first set of rows and the second set of rows to match corresponding sets of rows of the second version of the database by performing, for the first and second sets of rows, implicit catalog row conversion including:
• making the first and second sets of rows compatible with the second version of the database;
• and
• updating the first and second sets of rows to refer to the second version of the database instead of the first version;
• wherein:
• the database instance includes processes and memory structures of a database engine.