DHIS 2 now only supports PostgreSQL as database platform. Minimum required version is 9.4, however version 10 is recommended. The PostGIS extension for spatial data is also recommended.
The Tracked Entity object is renamed to Tracked Entity Type in the web API.
Tracked entity types are associated with tracked entity attributes.
The link between user roles and data sets and programs has been replaced by the new data write sharing levels.
The system settings API only accepts supported system setting keys. This implies that custom setting keys will no longer be supported. Apps and clients which are using custom system settings for data storage should be migrated to using the data store API.
Only web API versions from 2.26 and up are now supported (/api/24, /api/25 etc have been removed).