A zero downtime upgrade of a source system to a target system is initiated. The source system and the target system operate in a first database layer and a second database layer. Thereafter, differences in structure and/or database type are computed between a source table in the source system and a target table in the target system in each of the two different database layers. The data is then migrated, using the computing differences and in the second database layer, from the source table to the target table. The upgrade procedure is later terminated after completion of the migration of the data. Related apparatus, systems, techniques and articles are also described.