code:500, FATAL: remaining connection slots are reserved for non-replication superuser connections, Internal server error

Error Message

ArcGIS Pro allows adding services from ArcGIS Enterprise through Portal for ArcGIS. In certain cases, adding a service from ArcGIS Enterprise to ArcGIS Pro fails, and returns the following error message:

Error:   
code:500, FATAL: remaining connection slots are reserved for non-replication superuser connections, Internal server error.

This error message may be displayed along with another error message, "Error: Failed to add data: <Service URL>", in ArcGIS Pro.

Cause

The maximum number of connections allowed to the relational data store has been reached. The connection limit also includes the ArcGIS Data Store internal processes, which take up to five connections.

Solution or Workaround

Use the following workflow to resolve the error message and add the services from ArcGIS Enterprise to ArcGIS Pro.

Note:
On the ArcGIS Data Store machine, run the describedatastore command utility to check the maximum number of connections allowed to the relational data store. Refer to ArcGIS Enterprise: ArcGIS Data Store command utility reference for more information.

1. On the ArcGIS Data Store machine, run the changedbproperties command utility to increase the maximum number of connections allowed to the relational data store.

Note:
Ensure the machine has enough resources before increasing the maximum number of connections allowed in ArcGIS Data Store.

2. Restart the ArcGIS Data Store service.
   1. Type Services in the taskbar’s search box, and press Enter.
   2. Click the Services option from the results to open the console.
   3. Right-click the ArcGIS Data Store service and select the Restart option from the drop-down list.