[Mondrian] Cell-by-cell vs. Block Computation Mode

Matt Campbell mcampbell at pentaho.com
Fri May 8 09:25:29 EDT 2015


My loose understanding of Analysis Services cell evaluation is that it subdivides the cell space of a query into subcubes based on the calculations required by each set of intersections.  Within these smaller units it can then do things like identify invariants and default values that can be used on sparse datasets.  I think this is effectively what they mean by block computation, i.e. building up an optimized physical plan by breaking the cells required into units.

Mondrian doesn't currently do anything like this.  It has optimizations which attempt to reduce the evaluation cell space up front (so-called native evaluation), as well as batch together cell requests.  But there is currently nothing like what SSAS does in terms of breaking cell space down into subcubes and doing block evaluation.  I think there are lessons we could take from Microsoft here, and evaluation optimizations like this could certainly improve Mondrian's performance, particularly around large, sparse datasets and high cardinality dimensions.  Maybe we can borrow some of the SSAS engineering team for it, they don't seem busy.  :)


From: mondrian-bounces at pentaho.org [mailto:mondrian-bounces at pentaho.org] On Behalf Of Kleyson Rios
Sent: Thursday, May 07, 2015 9:47 AM
To: 'Mondrian developer mailing list'
Subject: [Mondrian] Cell-by-cell vs. Block Computation Mode

Last weeks I've read and studied a lot about MDX.

Almost all documents is based on Microsoft SSAS.

Some documents are about query performance, saying to avoid MDX queries that use cell-by-cell computation mode and use some techniques and functions that work in a Block Computation Mode.

Is the Mondrian engine optimized to execute some functions in Block Computation Mode ?

If yes, where can I find the optimized functions list ?

I couldn't find no reference about that subject for Mondrian.


Regards.

--
Kleyson Rios
Gestor Estadual em Tecnologia da Informação
Gerência de Tecnologia da Informação
Secretaria de Estado da Saúde de Goiás
(62) 3201-3707

Se não pode vencer pelo talento, vença pelo esforço. (Dave Weinbaum)

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