[Mondrian] Adding Grouping Set support for Distinct Count measures

Julian Hyde jhyde at pentaho.org
Thu Jan 24 23:27:32 EST 2008


Matt,
 
That rationale is useful - thanks.
 
Did you try against Teradata? I am a little hazy on what combinations of
grouping sets/distinct-count/AJIs they support, but it's possible that
distinct-count + grouping sets may prevent usage of an AJI, and that would
be unfortunate because AJIs give a big boost to performance.
 
You didn't answer my 2nd question: Would this work with distinct-count
measures applied to aggregate members? (For example unit sales over [CA plus
OR].)
 
Julian


  _____  

From: mondrian-bounces at pentaho.org [mailto:mondrian-bounces at pentaho.org] On
Behalf Of Matt Campbell
Sent: Thursday, January 24, 2008 7:38 AM
To: jhyde at pentaho.org; Mondrian developer mailing list
Subject: Re: [Mondrian] Adding Grouping Set support for Distinct Count
measures


We're interested in this change not so much for performance (although we
have seen some cases where it seems to improve performance) but because:

1) It will allow correct totaling in cases where a dimension table does not
join to every fact table row.  We can get over-counting in these cases
because the total query is fired separately without joining to the dimension
table.  I know in general dimension rows should be all-inclusive, ie have a
member value for each fact table row.  We have some good reasons for
violating this rule, though. 

2) It will also bring greater consistency to how count distinct and summable
measures are evaluated.




On Jan 22, 2008 7:52 PM, Julian Hyde < jhyde at pentaho.org
<mailto:jhyde at pentaho.org> > wrote:


No objections in principle. Have you hand-generated such queries to see
whether they are any improvement? It is possible that the queries do not
yield any performance improvement, because distinct-count is difficult for a
database to evaluate and therefore it might be difficult for the DBMS to
find commonality between the different grouping sets.
 
Would this work with distinct-count measures applied to aggregate members?
(For example unit sales over [CA plus OR].)
 
Julian


  _____  

From: mondrian-bounces at pentaho.org [mailto:mondrian-bounces at pentaho.org] On
Behalf Of Ajit Vasudeo Joglekar
Sent: Tuesday, January 22, 2008 9:33 AM
To: mondrian at pentaho.org
Subject: [Mondrian] Adding Grouping Set support for Distinct Count measures



We would like to introduce grouping sets support for distinct count measures
in mondrian. We have analyzed this and it is a small change. Most of the
work is around changing and adding test cases. 

It will be great if we can make this a part of the upcoming release.
Requesting comments 

Thanks 

-Ajit 




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