|Named Sets and Block Computation in SSAS 2012|
|Written by Chris Webb|
|Thursday, 17 May 2012 02:52|
Reposted from Chris Webb's blog with the author's permission.
Greg Galloway (who really should blog more often!) recently came across an otherwise undocumented query performance optimisation in SSAS 2012: using named sets inside aggregate functions in MDX no longer prevents the use of block computation/bulk mode. This was something that was explicitly called out as a Bad Thing To Do in Books Online (the link to the page in question is now dead though, possibly because it’s being updated), but here’s an example of a query that will now run much faster in SSAS 2012 Multidimensional than it used to in R2:
There are still situations where block computation can’t be used however, namely when the Current() function is used (which are going to be very rare I think):
Thanks also to Jeffrey Wang for the background on this.