In a system with more than 3.5 million rows in the note_data table, the performance of the /note-types endpoint is extremely slow. A call to the endpoint (as performed, for example, by the Courses UI) takes more than 15 seconds. The mod-notes log shows a warning:

You can see that the seemingly innocent SQL query results in a sequential scan on all rows of the note_type table.

This is on a system running Kiwi HF 3.