Issue

Different environments are running on different PostgreSQL versions, even if these environments are on the same licensed node.

Environment

Applications hosted in Mendix Cloud

Cause

From 01 July 2026, PostgreSQL 17.9 was set as the default version in our platform. Several maintenance waves were scheduled, and the majority of the environments hosted in Mendix Cloud were migrated to this version.

After some reports of performance issues related to PostgreSQL 17, Mendix made the decision to change the default version to 15.19 starting on 11 September 2026. No maintenances were scheduled to make a mass migration to this version, however. Migrations are handled on case-by-case need.

Environments that were created post 11 September 2026 run on PostgreSQL 15.19. For pre-existing environments to be migrated, a destructive task to the database must be performed.

This will be the case until PostgreSQL 17 is once again the default version. This is planned for 01 February 2027. After this date, maintenances will run to migrate all environments hosted in Mendix Cloud to that major version. The minor version is yet to be determined.

Maintenance warnings will apply with the usual time in advance.

Solution / Workaround

In order to have all environments of a node running in the same PostgreSQL version, the environments that are not running in PostgreSQL 15.19 must undergo a destructive task to the database. This will lead to a new RDS instance being created, which will start in the default PostgreSQL version.

It is possible to confirm the Database Version in the General tab of each environment, in Mendix Portal.

There are two types of destructive tasks: downsizing the container size, and clearing the database and model. 

To perform a downsize to an environment:

1. Submit a request for an upgrade to the container size.
2. Wait (at least) 6 hours for the cooldown time needed between tasks performed to the database.
3. Submit a request for a downgrade to the container size.

Steps 1 and 2 can be done via Self Service or via a ticket with Mendix Support, if Self Service is not enabled for the company. We advise planning these actions carefully, taking into account the cooldown time.

If the company does not have enough resources for an upgrade request, or clearing the database and model is the preferred route, a ticket should be submitted to Mendix Support.

If the environment is running on a container smaller than XXXL21, Mendix Support can clear the database and model of the environment. This is advised against for bigger environments.

If the environment is running on a container larger than XXXL21, Mendix Support will add extra database storage to the environment. After the cooldown time, Mendix Support will schedule a downsize task for the next maintenance window, to remove the extra database storage added. It is possible to click Execute Now at any point between scheduling the task and the maintenance window.

Any of these paths will result in the environment running in the default PostgreSQL version, which is 15.19.

Additional information

• Mendix documentation: 
  • Environment Details
  • Changing Your Plan in Mendix Cloud 
• Related KBA:
  • How to verify the PostgreSQL database version in Mendix Cloud applications
  • Query performance and modelling optimisation guideline in PostgreSQL17