def derived_memory_used_max_over_time_period
    end_date = Time.now.utc.beginning_of_day - 1
    perfs = VimPerformanceAnalysis.find_perf_for_time_period(self, "daily", :end_date => end_date, :days => Metric::LongTermAverages::AVG_DAYS)
    perfs.collect(&:abs_max_derived_memory_used_value).compact.max