Comment 5 for bug 1839527

Still, something is happening in ubuntu where we still get the conservative 1024*1024 value, and we do have systemd 240 in eoan. I removed the 5000 setting from the mysql service file, issued daemon-reload, and I still get 1024*1024.

In any case, by forcing a larger limit, I was able to reproduce the issue.

UPDATE: ah, there is a change in the debian/ubuntu packaging:
systemd (240-2) unstable; urgency=medium
...
  * Don't bump fs.nr_open in PID 1.
    In v240, systemd bumped fs.nr_open in PID 1 to the highest possible
    value. Processes that are spawned directly by systemd, will have
    RLIMIT_NOFILE be set to 512K (hard).
...