Describe the bug
When you have over several hundred thousand Data Sources or Graphs, additional sort variables should be tuned including 'innodb_sort_buffer_size' and 'sort_buffer_size' to have the sort indexes created in memory.

To Reproduce
Steps to reproduce the behavior:

1. Source Data Sources by Name Cache for very large number of Data Sources
2. Adjust the innodb_sort_buffer_size to a larger number like 200M
3. Restart mariadb and warm up the table
4. Sort again and see the performance difference

Expected behavior
Better performance.

Additional context
There are notes that starting with MySQL 5.6, the sort buffer size is dynamic upto the max settings, so it does not have the same significant effect as it used to have in prior MySQL versions.