DAX Measure Reference Performance

[Jayshamone]

Hello,

I understand that using variables much more efficient than definining calculations multiple times within one measure. 
Calculating a ratio however, creates another performance question, I cannot find an answer to. The formula would be something like this (with a and b being measures that are already defined elsewhere):

   c:= IF(a && b; DIVIDE(a; b) - 1; BLANK())

Should I define a and b as variables within c?

Or are a and b considered as constant values within c after the first calculation which would make the measure reference more efficent?

Thank you

Justus

[amitchandak · Accepted solution]

@Jayshamone , something like this should be better

Measure =
Var _a =a
Var _b = b
return
if(isblank(_a) ||isblank(_b) ,DIVIDE(a-b; b) , blank)

[Greg_Deckler]

@Jayshamone VAR's are constants, they cannot be recalculated. So yes, you should define a and b as VAR's and use those var's in your final calculation.

[Jayshamone]

Thank you, @Greg_Deckler for your quick response.

So a and b would indeed be recalcualted in c?
This would mean that if I make a change to a, I would need to make the same change to var a in c making it harder to maintain.
 

[Greg_Deckler]

@Jayshamone I'm not sure what you are saying by recalculate. VAR's do not recalculate:

Measure =
  VAR __a = [a]
  VAR __b = [b]
RETURN
  IF(ISBLANK(__a) || ISBLANK(__b),BLANK(),DIVIDE(__a, __b,BLANK()) - 1)