Forum Discussion
Performance : calculating Moving average, percentile
Good morning, everyone,
I would like to present to you a case where performance is poor.
The context is this: a date dimension table (this one includes all dates with hh:mm:ss) + a fact table ("PDJ") that contains two columns, one datetime column + one measure "M1".
Date M1
01/11/2018 04:10:01 4
01/11/2018 04:10:04 1
01/11/2018 04:10:05 1
01/11/2018 04:10:07 3
01/11/2018 04:10:08 8
01/11/2018 04:10:09 1
I have to calculate the moving averages (1s, 2s, 5s, 10s, 30s, 60s). We see in the example that the seconds do not follow one another. First of all, I had to feed the non-existent lines by putting 0 in the "M1" measure (Power query) to perform the moving averages.
Date M1
01/11/2018 04:10:01 4
01/11/2018 04:10:02 0
01/11/2018 04:10:03 0
01/11/2018 04:10:04 1
01/11/2018 04:10:05 1
01/11/2018 04:10:06 0
01/11/2018 04:10:07 3
01/11/2018 04:10:08 8
01/11/2018 04:10:09 1
For the calculation of the moving average, I have added an index.
Date M1 Index
01/11/2018 04:10:01 4 1
01/11/2018 04:10:02 0 2
01/11/2018 04:10:03 0 3
01/11/2018 04:10:04 1 4
01/11/2018 04:10:05 1 5
01/11/2018 04:10:06 0 6
01/11/2018 04:10:07 3 7
01/11/2018 04:10:08 8 8
01/11/2018 04:10:09 1 9
The following formula for example for 10s:
AverageMoving10s = CALCULATE(
AVERAGEX(VALUES(PDJ[Index]); PDJ[Total M1])
PDJ[Index] < VALUES(PDJ[Index]) +10 && PDJ[Index] >= VALUES(PDJ[Index])
)
The request was to display the maximum value on the different moving averages with the following formula:
Max10s =
MAXX(
values(PDJ[Index]);
[MoyMob10s]
)
I have encountered many performance problems.
First of all, feed a Date dimension table with all the seconds. I took an interval over 1 month but the customer wants 1 year: -(
The fact table with injection of non-existent lines (merge between the fact table and the dimension table in Power Query).
Adding an index.
Then, the calculated measures are long to display. I'm limited to one minute because beyond that, it crashes.
The customer has Power BI Pro. Storage: import data
Do you have any advice on how to make the analysis more efficient?
Thank you very much for your suggestions.
Jacky.
Can you try changing the last 2 bits:
'Fact'[TimeID] >= MovingWindowStart
&& 'Fact'[TimeID] <= MovingWindowEndto
'DimTime'[TimeKey] >= MovingWindowStart
&& 'DimTime'[TimeKey] <= MovingWindowEndIn addition, make sure TimeKey should be an integer.
6 Replies
Try splitting the Date column into 2 columns: Date & Time
Then have 2 seperate dimension tables for Date and Time.
That should reduce the model size and improve performance. Since Date & Time dimension table are Contiguous, you may not need an Index column.
Thank you. It's a great idea about two seperate dimension tables for Date and Time.
I could reduce the performance.But how do you fill the lines without measures ? To calculate average moving, you have to find all the seconds into the fact table.
And from my source, i have holes because i don't have all the seconds. i have to load the other lines with a measure to 0 with a outer join in Power Query (Merge between dimension date&time and the fact table)
Without index, it means that you use time for the calculation, isn't it ?
May be with this calculated measure :
MovingAverage = CALCULATE(AVERAGE([Value]),FILTER(MovingAverage, EARLIER([Time])>=[Time]))
Thank you.
You should have a Date dimension (365 rows for 1 year) & a time dimension (86400 rows for one day), and link it to your fact table.
Afterwards, you can derive your moving Average based on the Time dimension table which has all the time.
AverageMoving2s = VAR MovingWindowEnd = MAX ( 'Time'[TimeID] ) VAR MovingWindowStart = MovingWindowEnd - 2 VAR MaxTimeinFact = CALCULATE ( MAX ( 'Fact'[TimeID] ), ALLSELECTED ( 'Time' ) ) VAR MinTimeinFact = CALCULATE ( MIN ( 'Fact'[TimeID] ), ALLSELECTED ( 'Time' ) ) RETURN IF ( MovingWindowEnd <= MaxTimeinFact && MovingWindowEnd >= MinTimeinFact, CALCULATE ( AVERAGEX ( VALUES ( 'Time'[TimeID] ), VAR Total = [M1 Total] RETURN IF ( ISBLANK ( Total ), 0, Total ) ), ALL ( 'Time' ), 'Time'[TimeID] >= MovingWindowStart && 'Time'[TimeID] <= MovingWindowEnd ) )