Heads up: for DHIS 2 version 2.31 we will require PostgreSQL version 9.6 or higher.
This is in order to take advantage of certain SQL features introduced in that version. The current required version is 9.4.
If you plan to upgrade your PostgreSQL version we recommend going straight to version 10, as it contains several great features and performance improvements. Also, we will eventually require this version and so going directly to version 10 will avoid multiple successive upgrades.