Too many dimensions per fact?

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Too many dimensions per fact?

Post  chade25 on Tue Feb 19, 2013 1:45 pm

Is it possible to have too many dimensions per fact table? Right now I have 19 dimensions on one fact table, and I could add more.

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RE: Too many dimensions per fact?

Post  hkandpal on Tue Feb 19, 2013 2:26 pm

Hi,

you can have as many as you can , but after 20 it is better you see if you can combine some dimension into a Junk dimn.

thanks

HImanshu

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Re: Too many dimensions per fact?

Post  BoxesAndLines on Tue Feb 19, 2013 10:46 pm

It starts to increase the load times due to all the indexing normally required for FK indexes. That said, I've blown by 20 many times. :-)
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Re: Too many dimensions per fact?

Post  Mike Honey on Wed Feb 20, 2013 1:16 am

Each new dimension decreases the flexibility of your model - it is much easier to add or change attributes in an existing dimension than add a new dimension. So I tend to lean in that direction e.g. a single Customers dim with many attributes rather than Customer Type dim, Customer Location dim, etc.

Another consideration is the increasing complexity of the end user experience: whether coding star joins or using an OLAP tool you may be making life harder for your testers, report authors and users.

Balanced against that, it can be confusing when junk dimension attributes have absolutely no association with each other.
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