If we change levels and new intervals are not multiples of old intervals, decimation will erase all the stats that was collected before the levels change. Is that correct?
Yes, if new decimation levels are not aligned with the prior ones then older data may be lost. e.g. if the existing stats were decimated to 1 stat per every 7 minutes and it's changed to 1 every 9 minutes then the alignment is off except every 63 minutes.
I guess we should prevent stats disappearance