[Mondrian] virtual cubes, non-joining dims, performance

Wright, Jeff jeff.s.wright at truvenhealth.com
Fri Aug 19 10:26:30 EDT 2016

I think this is primarily to Matt, but sending to mailing list in case there's other interest or input...

We've been testing some new-ish code in an effort to get correct behavior of non-joining dimensions, and there seems to be a somewhat steep performance cost to the fix. What we're seeing is that recent versions of SqlTupleReader generate an expensive UNION query across the fact tables in a virtual cube.

I haven't carefully sorted through the code our team has tested, but looking at the revision history on github, I suspect we're testing with the checkin for issue #1, but not issue #2:

#1 - http://jira.pentaho.com/browse/MONDRIAN-1599 - Some queries against Virtual cubes can give wrong results when dimensions don't fully join
#2 - http://jira.pentaho.com/browse/MONDRIAN-2280 - ValidMeasure not taken into account when Analyzer uses NonEmptyCrossjoin as it returns no data

Is the expensive UNION query something you've seen as well?

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