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cognos 10 with SSAS: issues


cognos 10 with SSAS: issues

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snap254
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Hi

We're considering implementing a Cognos 10 reporting layer on top of SSAS 2008 R2 and were wondering if there are any obvious drawbacks to this apart from things like cost.

Does anyone have any insights - specifically to Cognos 10?

thanks
A
Koen Verbeeck
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My experience with Cognos is about Cognos 8, but from what I've heard that's pretty much the same.

To use Cognos on top of SSAS, you need to create a dummy framework in Cognos Framework manager. Publish that and you can use the SSAS metadata in your reports.

However, Cognos can produce some pretty horrid MDX, so it's possible that some reports (depends on design) have pretty bad performance.


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Yes I confirm, performance are very bad compared to Excel.

Cognos Analysis Studio on SSAS works very bad as soon as you have more than 2 dimensions in rows and more than 300 rows...

A query can last hours in Cognos while running in 5 mn in Excel...
Koen Verbeeck
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renaud.durand (3/29/2012)
Yes I confirm, performance are very bad compared to Excel.

Cognos Analysis Studio on SSAS works very bad as soon as you have more than 2 dimensions in rows and more than 300 rows...

A query can last hours in Cognos while running in 5 mn in Excel...


300 rows for an analysis? Isn't that a bit much? The human mind can only process around 10-20 lines in a table efficiently.

The advantage of Analysis Studio over Excel is that it is somewhat easier to do calculations. In Excel, you are a bit stuck on the PivotTable layout, unless you convert everything to formulas. But then you can't pivot anymore.


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Another issues is that, once you have the SSAS Cubes in cognos Framework manager, you cannot make any changes to it. Basically, you have to do all the modeling in SSAS before you publish it and have cognos comsume it.
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amaramoosa (4/11/2012)
Another issues is that, once you have the SSAS Cubes in cognos Framework manager, you cannot make any changes to it. Basically, you have to do all the modeling in SSAS before you publish it and have cognos comsume it.


You can still create your own calculations in Report/Analysis studio.


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Calculations can be incorporated into Excel pivot tables using a free add-in for Excel, OLAP Pivot Table Extensions. It's available from codeplex.

I also confirm performance problems with both Cognos 8 and 10 against SSAS cubes. Essentially, the MDX queries from Cognos are written such that all members of each dimension used in a report are retrieved then mashed up within the Cognos query engine. This approach bypasses the performance advantages gained by allowing SSAS to determine the intersecting data points between dimensions for example by using the non empty function in the MDX query.

In Cognos 10, there is something called DQM, data query manager, which is supposed to address the performance issues by having the dimensional mashup processed in memory. However, DQM does not yet support all of the possible features of an SSAS cube such as named sets so it cannot be used at this time unfortunately.
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Hi,

I have done Cognos 10 integration with SSAS cubes. Once you have created the framework package you can then make changes to the cube and it will refresh ok once you log out of Cognos and log in again. The framework manager package stores the name of the AS database and the names of the cubes in the database. So changes to dimensions, additional dimensions, new measure groups, new calculation and new sets all become available in Cognos once you log in again.
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