Measure average system load on oracle database instance

Short overview over utilization of DB system.
Lists average and peak values for every instance (in case of RAC) for given time range:
– Total number of active DB sessions
– Number of active DB sessions on CPU (no other wait event)

Value and timestamp are shown for:
– maximum peak load
– average load over total time range
– maximum average load over one minute
– maximum average load over one hour

SELECT /* DB-Tools Ramm average system load */
       Instance_Number, MIN(Sample_Time) Start_Range, MAX(Sample_Time) End_Range,
       MAX(Active)                                                          Max_Active,
       MAX(Sample_Time) KEEP (DENSE_RANK LAST ORDER BY Active)              Max_Active_Sample_Time, 
       MAX(CPU)                                                             Max_CPU,
       MAX(Sample_Time) KEEP (DENSE_RANK LAST ORDER BY CPU)                 Max_CPU_Sample_Time, 
       ROUND(AVG(Active),1)                                                 Avg_Active_Total,
       ROUND(AVG(CPU),1)                                                    Avg_CPU_Total,
       ROUND(MAX(Avg_Active_Minute),1)                                      Max_Avg_Active_Minute,
       MAX(Sample_Time) KEEP (DENSE_RANK LAST ORDER BY Avg_Active_Minute)   Max_Avg_Active_Minute_End, 
       ROUND(MAX(Avg_CPU_Minute),1)                                         Max_Avg_CPU_Minute,
       MAX(Sample_Time) KEEP (DENSE_RANK LAST ORDER BY Avg_CPU_Minute)      Max_Avg_CPU_Minute_End, 
       ROUND(MAX(Avg_Active_Hour),1)                                        Max_Avg_Active_Hour,
       MAX(Sample_Time) KEEP (DENSE_RANK LAST ORDER BY Avg_Active_Hour)     Max_Avg_Active_Hour_End, 
       ROUND(MAX(Avg_CPU_Hour),1)                                           Max_Avg_CPU_Hour,
       MAX(Sample_Time) KEEP (DENSE_RANK LAST ORDER BY Avg_CPU_Hour)        Max_Avg_CPU_Hour_End 
FROM   ( 
        SELECT h.*,
               AVG(Active) OVER (PARTITION BY Instance_Number, TRUNC(Sample_Time, 'MI'))    Avg_Active_Minute,      
               AVG(Active) OVER (PARTITION BY Instance_Number, TRUNC(Sample_Time, 'HH24'))  Avg_Active_Hour,      
               AVG(CPU) OVER (PARTITION BY Instance_Number, TRUNC(Sample_Time, 'MI'))       Avg_CPU_Minute,      
               AVG(CPU) OVER (PARTITION BY Instance_Number, TRUNC(Sample_Time, 'HH24'))     Avg_CPU_Hour      
        FROM   (
                SELECT /*+ NO_MERGE LEADING(h.ash) PARALLEL(h,4) */ 
                       Instance_Number, Sample_Time, 
                       COUNT(*) Active,
                       SUM(CASE WHEN Session_State = 'ON CPU' THEN 1 ELSE 0 END) CPU  
                FROM   DBA_Hist_Active_Sess_History h
                WHERE  Sample_Time > SYSTIMESTAMP - 4
                AND    NVL(Event, Session_State) NOT IN ('PX Deq Credit: send blkd') -- Idle-Events nicht zaehlen
                GROUP BY Instance_Number, Sample_Time
               ) h
       )
GROUP BY Instance_Number       
;