thx @rlkoshak,
well, one value per day is absolutely fine. i am planning on doing the following:
i will count the ticks in a Number item “usage_now”.
a rule that triggers every day at 23:59 will then write that value to a second persisted number item “usage_day”.
so i guess 365 values for “usage_day” should fit inside a rrd4j database?
i already have rrd4j set up (for temperatures) so i just have to add “usage_now” and “usage_day” to it.
still i need to persist every minute, even if the value for “usage_day” is written only once a day?