Hey @gwillem, not quite sure what you mean about ‘500k’ objects. Can you give an example of what your data looks like?
The primary thing re: cardinality is the unique combinations of measurement + tags + fields. This is a very good rundown of how the count works, and provided you keep your cardinality as low as possible you should be able to write/read all of your data without problem!
Also, we’ve had a few discussions on this here in the community so maybe some of this will help too?
