[Mondrian] Does order of dimension in NECJ matter with regards to performance?

Zelaine Fong zfong at lucidera.com
Thu Sep 27 11:48:01 EDT 2007


If possible, Mondrian will try to evaluate the NECJ natively in the 
RDBMS.  See rolap.RolapNativeCrossJoin for details on cases that aren't 
handled.  Also, if you look at rolap.NonEmptyTest and look at the cases 
that call checkNotNative, that will give some examples of cases where 
the NECJ is not processed natively.

-- Zelaine

Peter Tran wrote:
> Hi Zelaine,
> 
> Do we really delegate all these NECJ to the underlying RDBMS?  Are you
> saying that we actually generate a SQL that joins across all those
> dimensions?  That's not what I'm seeing when I turn on the trace to view
> the actual SQL.
> 
> It looks like we do some of this filtering internally in memory within
> Mondrian.
> 
> Am I wrong?
> 
> Thanks,
> -Peter
> 
> -----Original Message-----
> From: mondrian-bounces at pentaho.org [mailto:mondrian-bounces at pentaho.org]
> On Behalf Of Zelaine Fong
> Sent: Thursday, September 27, 2007 10:17 AM
> To: Mondrian developer mailing list
> Subject: Re: [Mondrian] Does order of dimension in NECJ matter with
> regardsto performance?
> 
> It shouldn't, unless the underlying DBMS you're using has limitations in
> 
> how it optimizes join queries.
> 
> -- Zelaine
> 
> Peter Tran wrote:
>> Hi,
>>
>> If I have multiple dimensions nested within NECJ, does the order of
> the
>> dimension sets have any impact on performance?
>>
>> For example:
>>
>> NECJ(NECJ(NECJ(NECJ(dim1, dim2), dim3), dim4), dim5)
>>
>> vs.
>>
>> NECJ(NECJ(NECJ(NECJ(dim5, dim4), dim3), dim2), dim1)
>>
>> Thanks,
>> -Peter
>>
>>
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