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Analysis Services - Dimension Storage

ssas1 Analysis Services   Dimension Storage SSAS Dimension Storage


Now here is the rub when it comes to aggregated data. A cube stores aggregated data based on the hierarchies in our dimensions. So depending on how many dimensions and how many measures we have we can start getting quite a big cube on the hard disk and memory. So just how far should we be going with the storage. i.e. how much should be physically stored agregations on the disk versus calculated on the fly?

What is Dimension Storage ?

Dimension Storage is the means to instruct Analysis Services how to store the information on the cube. Also it controls how the dimension is going to work on the actual data. This needs clearer definition as it is a two for one, physical storage capability and frequency of update. This is where the terms ROLAP & MOLAP come in.

ROLAP – Realtime OLAP – This means that the data is coming from a system that is constantly changing. So examples of where you would use ROLAP are when refering to volotile data such as stock market where information may need to be updated on the fly. You done want to instruct Analysis Services to be constantly updating aggreations. So ROLAP is generally slow as it is (depending on setting) constantly looking for changes.
MOLAP – Multidimensional OLAP – This means the data is more static and is updated at set intervals. This is the most common approach to cube building as people want to see what was done up to close of business yesterday.

This is another setting called HOLAP but this is discussed later on the Cube itself.

the final thing to stress is the aggreagtions are stored in the Cube NOT in the dimension, we need to define the dimension storage as this alters the way the cube reacts. The best example to bring up is the Measure group of sales which is on ROLAP information is constantly being added to the cube realtime. Now one of the sales lines introduces a new customer which is not in the cube when the cube processes it will error becuase teh customer dimension is processed once a day and does not have this customer. So you would have to change the Dimension Storage method from MOLAP to ROLAP on the Customer to allow for correct processing. Now sticking with this example what about the date dimension, for Dimension Storage would it use ROLAP or MOLAP? the answer would be MOLAP because your date dimension is non volatile and generally will cover not only dates in the past but also the future (typical date dimesnions would have date going up to at least the year 2050).

This video is one of many SSAS tutorials on this site click here for more.

The Dimension Storage example files

To obtain the sample files please click here:

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9 Comments

  1. kingingway says
    20 Apr 15 at 5:18am

    Nice one.
    You really are gifted with the way you explain issues. I haven’t heard from
    you in years though. Looking forward to seeing more of you through your
    teaching

  2. shankho das says
    05 Nov 14 at 11:41am

    Great Explanation .

  3. Sunil Rana says
    10 Oct 13 at 11:15am

    Awesome Videos, thanks man…you saved lot of my time…nice videos..nice content…seriously hats off… :)

  4. Yazan Inaim says
    29 Aug 12 at 4:19pm

    I love the way he demonstrate and facilitate this subject !

  5. GUNEET KALRA says
    24 Aug 12 at 5:30am

    Excellent video :) thanks a lot for clearing this out..

  6. kohlismunishk says
    24 Jun 12 at 8:18am

    You can’t get more clear and concise explanation. Very educative and well explained videos on MSAS.

  7. 24 Jun 12 at 8:18am

    [..YouTube..] You can’t get more clear and concise explanation. Very educative and well explained videos on MSAS.

  8. JimiLiendrix says
    24 Jun 12 at 2:35am

    Thanks!

  9. 24 Jun 12 at 2:35am

    [..YouTube..] Thanks!

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